Internet Engineering Task Force (IETF) T. Eckert, Ed.
Request for Comments: 8994 Futurewei USA
Category: Standards Track M. Behringer, Ed.
ISSN: 2070-1721
S. Bjarnason
Arbor Networks
May 2021
An Autonomic Control Plane (ACP)
Abstract
Autonomic functions need a control plane to communicate, which
depends on some addressing and routing. This Autonomic Control Plane
should ideally be self-managing and be as independent as possible of
configuration. This document defines such a plane and calls it the
"Autonomic Control Plane", with the primary use as a control plane
for autonomic functions. It also serves as a "virtual out-of-band
channel" for Operations, Administration, and Management (OAM)
communications over a network that provides automatically configured,
hop-by-hop authenticated and encrypted communications via
automatically configured IPv6 even when the network is not configured
or is misconfigured.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8994.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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described in the Simplified BSD License.
Table of Contents
1. Introduction (Informative)
1.1. Applicability and Scope
2. Acronyms and Terminology (Informative)
3. Use Cases for an Autonomic Control Plane (Informative)
3.1. An Infrastructure for Autonomic Functions
3.2. Secure Bootstrap over an Unconfigured Network
3.3. Permanent Reachability Independent of the Data Plane
4. Requirements (Informative)
5. Overview (Informative)
6. Self-Creation of an Autonomic Control Plane (ACP) (Normative)
6.1. Requirements for the Use of Transport Layer Security (TLS)
6.2. ACP Domain, Certificate, and Network
6.2.1. ACP Certificates
6.2.2. ACP Certificate AcpNodeName
6.2.2.1. AcpNodeName ASN.1 Module
6.2.3. ACP Domain Membership Check
6.2.3.1. Realtime Clock and Time Validation
6.2.4. Trust Anchors (TA)
6.2.5. Certificate and Trust Anchor Maintenance
6.2.5.1. GRASP Objective for EST Server
6.2.5.2. Renewal
6.2.5.3. Certificate Revocation Lists (CRLs)
6.2.5.4. Lifetimes
6.2.5.5. Reenrollment
6.2.5.6. Failing Certificates
6.3. ACP Adjacency Table
6.4. Neighbor Discovery with DULL GRASP
6.5. Candidate ACP Neighbor Selection
6.6. Channel Selection
6.7. Candidate ACP Neighbor Verification
6.8. Security Association (Secure Channel) Protocols
6.8.1. General Considerations
6.8.2. Common Requirements
6.8.3. ACP via IPsec
6.8.3.1. Native IPsec
6.8.3.1.1. RFC 8221 (IPsec/ESP)
6.8.3.1.2. RFC 8247 (IKEv2)
6.8.3.2. IPsec with GRE Encapsulation
6.8.4. ACP via DTLS
6.8.5. ACP Secure Channel Profiles
6.9. GRASP in the ACP
6.9.1. GRASP as a Core Service of the ACP
6.9.2. ACP as the Security and Transport Substrate for GRASP
6.9.2.1. Discussion
6.10. Context Separation
6.11. Addressing inside the ACP
6.11.1. Fundamental Concepts of Autonomic Addressing
6.11.2. The ACP Addressing Base Scheme
6.11.3. ACP Zone Addressing Sub-Scheme (ACP-Zone)
6.11.4. ACP Manual Addressing Sub-Scheme (ACP-Manual)
6.11.5. ACP Vlong Addressing Sub-Scheme (ACP-Vlong-8/
ACP-Vlong-16)
6.11.6. Other ACP Addressing Sub-Schemes
6.11.7. ACP Registrars
6.11.7.1. Use of BRSKI or Other Mechanisms or Protocols
6.11.7.2. Unique Address/Prefix Allocation
6.11.7.3. Addressing Sub-Scheme Policies
6.11.7.4. Address/Prefix Persistence
6.11.7.5. Further Details
6.12. Routing in the ACP
6.12.1. ACP RPL Profile
6.12.1.1. Overview
6.12.1.1.1. Single Instance
6.12.1.1.2. Reconvergence
6.12.1.2. RPL Instances
6.12.1.3. Storing vs. Non-Storing Mode
6.12.1.4. DAO Policy
6.12.1.5. Path Metrics
6.12.1.6. Objective Function
6.12.1.7. DODAG Repair
6.12.1.8. Multicast
6.12.1.9. Security
6.12.1.10. P2P Communications
6.12.1.11. IPv6 Address Configuration
6.12.1.12. Administrative Parameters
6.12.1.13. RPL Packet Information
6.12.1.14. Unknown Destinations
6.13. General ACP Considerations
6.13.1. Performance
6.13.2. Addressing of Secure Channels
6.13.3. MTU
6.13.4. Multiple Links between Nodes
6.13.5. ACP Interfaces
6.13.5.1. ACP Loopback Interfaces
6.13.5.2. ACP Virtual Interfaces
6.13.5.2.1. ACP Point-to-Point Virtual Interfaces
6.13.5.2.2. ACP Multi-Access Virtual Interfaces
7. ACP Support on L2 Switches/Ports (Normative)
7.1. Why (Benefits of ACP on L2 Switches)
7.2. How (per L2 Port DULL GRASP)
8. Support for Non-ACP Components (Normative)
8.1. ACP Connect
8.1.1. Non-ACP Controller and/or Network Management System
(NMS)
8.1.2. Software Components
8.1.3. Autoconfiguration
8.1.4. Combined ACP and Data Plane Interface (VRF Select)
8.1.5. Use of GRASP
8.2. Connecting ACP Islands over Non-ACP L3 Networks (Remote ACP
Neighbors)
8.2.1. Configured Remote ACP Neighbor
8.2.2. Tunneled Remote ACP Neighbor
8.2.3. Summary
9. ACP Operations (Informative)
9.1. ACP (and BRSKI) Diagnostics
9.1.1. Secure Channel Peer Diagnostics
9.2. ACP Registrars
9.2.1. Registrar Interactions
9.2.2. Registrar Parameters
9.2.3. Certificate Renewal and Limitations
9.2.4. ACP Registrars with Sub-CA
9.2.5. Centralized Policy Control
9.3. Enabling and Disabling the ACP and/or the ANI
9.3.1. Filtering for Non-ACP/ANI Packets
9.3.2. "admin down" State
9.3.2.1. Security
9.3.2.2. Fast State Propagation and Diagnostics
9.3.2.3. Low-Level Link Diagnostics
9.3.2.4. Power Consumption Issues
9.3.3. Enabling Interface-Level ACP and ANI
9.3.4. Which Interfaces to Auto-Enable?
9.3.5. Enabling Node-Level ACP and ANI
9.3.5.1. Brownfield Nodes
9.3.5.2. Greenfield Nodes
9.3.6. Undoing "ANI/ACP enable"
9.3.7. Summary
9.4. Partial or Incremental Adoption
9.5. Configuration and the ACP (Summary)
10. Summary: Benefits (Informative)
10.1. Self-Healing Properties
10.2. Self-Protection Properties
10.2.1. From the Outside
10.2.2. From the Inside
10.3. The Administrator View
11. Security Considerations
12. IANA Considerations
13. References
13.1. Normative References
13.2. Informative References
Appendix A. Background and Future (Informative)
A.1. ACP Address Space Schemes
A.2. BRSKI Bootstrap (ANI)
A.3. ACP Neighbor Discovery Protocol Selection
A.3.1. LLDP
A.3.2. mDNS and L2 Support
A.3.3. Why DULL GRASP?
A.4. Choice of Routing Protocol (RPL)
A.5. ACP Information Distribution and Multicast
A.6. CAs, Domains, and Routing Subdomains
A.7. Intent for the ACP
A.8. Adopting ACP Concepts for Other Environments
A.9. Further (Future) Options
A.9.1. Auto-Aggregation of Routes
A.9.2. More Options for Avoiding IPv6 Data Plane Dependencies
A.9.3. ACP APIs and Operational Models (YANG)
A.9.4. RPL Enhancements
A.9.5. Role Assignments
A.9.6. Autonomic L3 Transit
A.9.7. Diagnostics
A.9.8. Avoiding and Dealing with Compromised ACP Nodes
A.9.9. Detecting ACP Secure Channel Downgrade Attacks
Acknowledgements
Contributors
Authors' Addresses
1. Introduction (Informative)
Autonomic Networking is a concept of self-management: autonomic
functions self-configure, and negotiate parameters and settings
across the network. "Autonomic Networking: Definitions and Design
Goals" [RFC7575] defines the fundamental ideas and design goals of
Autonomic Networking. A gap analysis of Autonomic Networking is
given in "General Gap Analysis for Autonomic Networking" [RFC7576].
The reference architecture for Autonomic Networking in the IETF is
specified in the document "A Reference Model for Autonomic
Networking" [RFC8993].
Autonomic functions need an autonomically built communications
infrastructure. This infrastructure needs to be secure, resilient,
and reusable by all autonomic functions. Section 5 of [RFC7575]
introduces that infrastructure and calls it the Autonomic Control
Plane (ACP). More descriptively, it could be called the "Autonomic
communications infrastructure for OAM and control". For naming
consistency with that prior document, this document continues to use
the name ACP.
Today, the OAM and control plane of IP networks is what is typically
called in-band management and/or signaling: its management and
control protocol traffic depends on the routing and forwarding
tables, security, policy, QoS, and potentially other configuration
that first has to be established through the very same management and
control protocols. Misconfigurations, including unexpected side
effects or mutual dependencies, can disrupt OAM and control
operations and especially disrupt remote management access to the
affected node itself and potentially disrupt access to a much larger
number of nodes for which the affected node is on the network path.
For an example of in-band management failing in the face of operator-
induced misconfiguration, see [FCC], for example, Section III.B.15 on
page 8:
| ...engineers almost immediately recognized that they had
| misdiagnosed the problem. However, they were unable to resolve
| the issue by restoring the link because the network management
| tools required to do so remotely relied on the same paths they had
| just disabled.
Traditionally, physically separate, so-called out-of-band
(management) networks have been used to avoid these problems or at
least to allow recovery from such problems. In the worst-case
scenario, personnel are sent on site to access devices through out-
of-band management ports (also called craft ports, serial consoles,
or management Ethernet ports). However, both options are expensive.
In increasingly automated networks, both centralized management
systems and distributed autonomic service agents in the network
require a control plane that is independent of the configuration of
the network they manage, to avoid impacting their own operations
through the configuration actions they take.
This document describes a modular design for a self-forming, self-
managing, and self-protecting ACP, which is a virtual out-of-band
network designed to be as independent as possible of configuration,
addressing, and routing to avoid the self-dependency problems of
current IP networks while still operating in-band on the same
physical network that it is controlling and managing. The ACP design
is therefore intended to combine as well as possible the resilience
of out-of-band management networks with the low cost of traditional
IP in-band network management. The details of how this is achieved
are described in Section 6.
In a fully Autonomic Network without legacy control or management
functions and/or protocols, the data plane would be just a forwarding
plane for "data" IPv6 packets, which are packets other than those
control and management plane packets forwarded by the ACP itself. In
such a network, there would be no non-autonomous control of nodes nor
a non-autonomous management plane.
Routing protocols would be built inside the ACP as autonomous
functions via autonomous service agents, leveraging the following ACP
functions instead of implementing them separately for each protocol:
discovery; automatically established, authenticated, and encrypted
local and distant peer connectivity for control and management
traffic; and common session and presentation functions of the control
and management protocol.
When ACP functionality is added to nodes that do not have autonomous
management plane and/or control plane functions (henceforth called
non-autonomous nodes), the ACP instead is best abstracted as a
special Virtual Routing and Forwarding (VRF) instance (or virtual
router), and the complete, preexisting, non-autonomous management
and/or control plane is considered to be part of the data plane to
avoid introducing more complex terminology only for this case.
Like the forwarding plane for "data" packets, the non-autonomous
control and management plane functions can then be managed and/or
used via the ACP. This terminology is consistent with preexisting
documents such as "Using an Autonomic Control Plane for Stable
Connectivity of Network Operations, Administration, and Maintenance
(OAM)" [RFC8368].
In both autonomous and non-autonomous instances, the ACP is built
such that it operates in the absence of the data plane. The ACP also
operates in the presence of any (mis)configured non-autonomous
management and/or control components in the data plane.
The ACP serves several purposes simultaneously:
1. Autonomic functions communicate over the ACP. The ACP therefore
directly supports Autonomic Networking functions, as described in
[RFC8993]. For example, GRASP ("GeneRic Autonomic Signaling
Protocol (GRASP)" [RFC8990]) runs securely inside the ACP and
depends on the ACP as its "security and transport substrate".
2. A controller or network management system can use ACP to securely
bootstrap network devices in remote locations, even if the (data
plane) network in between is not yet configured; no bootstrap
configuration that is dependent on the data plane is required.
An example of such a secure bootstrap process is described in
"Bootstrapping Remote Secure Key Infrastructure (BRSKI)"
[RFC8995].
3. An operator can use ACP to access remote devices using protocols
such as Secure SHell (SSH) or Network Configuration Protocol
(NETCONF), even if the network is misconfigured or unconfigured.
This document describes these purposes as use cases for the ACP in
Section 3, and it defines the requirements in Section 4. Section 5
gives an overview of how the ACP is constructed.
The normative part of this document starts with Section 6, where the
ACP is specified. Section 7 explains how to support ACP on Layer 2
(L2) switches (normative). Section 8 explains how non-ACP nodes and
networks can be integrated (normative).
The remaining sections are non-normative. Section 10 reviews the
benefits of the ACP (after all the details have been defined).
Section 9 provides operational recommendations. Appendix A provides
additional background and describes possible extensions that were not
applicable for this specification but were considered important to
document. There are no dependencies on Appendix A in order to build
a complete working and interoperable ACP according to this document.
The ACP provides secure IPv6 connectivity; therefore, it can be used
for secure connectivity not only for self-management as required for
the ACP in [RFC7575] but also for traditional (centralized)
management. The ACP can be implemented and operated without any
other components of Autonomic Networks, except for GRASP. ACP relies
on per-link Discovery Unsolicited Link-Local (DULL) GRASP (see
Section 6.4) to auto-discover ACP neighbors and includes the ACP
GRASP instance to provide service discovery for clients of the ACP
(see Section 6.9), including for its own maintenance of ACP
certificates.
The document [RFC8368] describes how the ACP can be used alone to
provide secure and stable connectivity for autonomic and non-
autonomic OAM applications, specifically for the case of current non-
autonomic networks and/or nodes. That document also explains how
existing management solutions can leverage the ACP in parallel with
traditional management models, when to use the ACP, and how to
integrate with potentially IPv4-only OAM backends.
Combining ACP with Bootstrapping Remote Secure Key Infrastructure
(BRSKI) (see [RFC8995]) results in the "Autonomic Network
Infrastructure" (ANI) as defined in [RFC8993], which provides
autonomic connectivity (from ACP) with secure zero-touch (automated)
bootstrap from BRSKI. The ANI itself does not constitute an
Autonomic Network, but it allows the building of more or less
Autonomic Networks on top of it, using either centralized automation
in SDN style (see "Software-Defined Networking (SDN): Layers and
Architecture Terminology" [RFC7426]) or distributed automation via
Autonomic Service Agents (ASA) and/or Autonomic Functions (AF), or a
mixture of both. See [RFC8993] for more information.
1.1. Applicability and Scope
Please see the following Terminology section (Section 2) for
explanations of terms used in this section.
The design of the ACP as defined in this document is considered to be
applicable to all types of "professionally managed" networks: Service
Provider, Local Area Network (LAN), Metropolitan Area Network (MAN/
Metro), Wide Area Network (WAN), Enterprise Information Technology
(IT) and Operational Technology (OT) networks. The ACP can operate
equally on Layer 3 (L3) equipment and on L2 equipment such as bridges
(see Section 7). The hop-by-hop authentication, integrity
protection, and confidentiality mechanism used by the ACP is defined
to be negotiable; therefore, it can be extended to environments with
different protocol preferences. The minimum implementation
requirements in this document attempt to achieve maximum
interoperability by requiring support for multiple options depending
on the type of device: IPsec (see "Security Architecture for the
Internet Protocol" [RFC4301]) and Datagram Transport Layer Security
(DTLS, see Section 6.8.4).
The implementation footprint of the ACP consists of Public Key
Infrastructure (PKI) code for the ACP certificate including EST (see
"Enrollment over Secure Transport" [RFC7030]), GRASP, UDP, TCP, and
Transport Layer Security (TLS, see Section 6.1). For more
information regarding the security and reliability of GRASP and for
EST, the ACP secure channel protocol used (such as IPsec or DTLS),
and an instance of IPv6 packet forwarding and routing via RPL, see
"RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks"
[RFC6550], which is separate from routing and forwarding for the data
plane (user traffic).
The ACP uses only IPv6 to avoid the complexity of dual-stack (both
IPv6 and IPv4) ACP operations. Nevertheless, it can be integrated
without any changes to otherwise IPv4-only network devices. The data
plane itself would not need to change, and it could continue to be
IPv4 only. For such IPv4-only devices, IPv6 itself would be
additional implementation footprint that is only required for the
ACP.
The protocol choices of the ACP are primarily based on wide use and
support in networks and devices, well-understood security properties,
and required scalability. The ACP design is an attempt to produce
the lowest risk combination of existing technologies and protocols to
build a widely applicable, operational network management solution.
RPL was chosen because it requires a smaller routing table footprint
in large networks compared to other routing protocols with an
autonomically configured single area. The deployment experience of
large-scale Internet of Things (IoT) networks serves as the basis for
wide deployment experience with RPL. The profile chosen for RPL in
the ACP does not leverage any RPL-specific forwarding plane features
(IPv6 extension headers), making its implementation a pure control
plane software requirement.
GRASP is the only completely novel protocol used in the ACP, and this
choice was necessary because there is no existing protocol suitable
for providing the necessary functions to the ACP, so GRASP was
developed to fill that gap.
The ACP design can be applicable to devices constrained with respect
to CPU and memory, and to networks constrained with respect to
bitrate and reliability, but this document does not attempt to define
the most constrained type of devices or networks to which the ACP is
applicable. RPL and DTLS for ACP secure channels are two protocol
choices already making ACP more applicable to constrained
environments. Support for constrained devices in this specification
is opportunistic, but not complete, because the reliable transport
for GRASP (see Section 6.9.2) only specifies TCP/TLS. See
Appendix A.8 for discussions about how future standards or
proprietary extensions and/or variations of the ACP could better meet
expectations that are different from those upon which the current
design is based, including supporting constrained devices better.
2. Acronyms and Terminology (Informative)
This document serves both as a normative specification for ACP node
behavior as well as an explanation of the context by providing
descriptions of requirements, benefits, architecture, and operational
aspects. Normative sections are labeled "(Normative)" and use BCP 14
keywords. Other sections are labeled "(Informative)" and do not use
those normative keywords.
In the rest of the document, we will refer to systems that use the
ACP as "nodes". Typically, such a node is a physical (network
equipment) device, but it can equally be some virtualized system.
Therefore, we do not refer to them as devices unless the context
specifically calls for a physical system.
This document introduces or uses the following terms (sorted
alphabetically). Introduced terms are explained on first use, so
this list is for reference only.
ACP: Autonomic Control Plane. The autonomic function as defined in
this document. It provides secure, zero-touch (automated)
transitive (network-wide) IPv6 connectivity for all nodes in the
same ACP domain as well as a GRASP instance running across this
ACP IPv6 connectivity. The ACP is primarily meant to be used as a
component of the ANI to enable Autonomic Networks, but it can
equally be used in simple ANI networks (with no other autonomic
functions) or completely by itself.
ACP address: An IPv6 address assigned to the ACP node. It is stored
in the acp-node-name of the ACP certificate.
ACP address range or set: The ACP address may imply a range or set
of addresses that the node can assign for different purposes.
This address range or set is derived by the node from the format
of the ACP address called the addressing sub-scheme.
ACP certificate: A Local Device IDentity (LDevID) certificate
conforming to "Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile"
[RFC5280] that carries the acp-node-name, which is used by the ACP
to learn its address in the ACP and to derive and
cryptographically assert its membership in the ACP domain. In the
context of the ANI, the ACP certificate is also called the ANI
certificate. In the context of AN, the ACP certificate is also
called the AN certificate.
ACP connect interface: An interface on an ACP node that provides
access to the ACP for non-ACP-capable nodes without using an ACP
secure channel. See Section 8.1.1.
ACP domain: The ACP domain is the set of nodes with ACP certificates
that allow them to authenticate each other as members of the ACP
domain. See also Section 6.2.3.
ACP loopback interface: The loopback interface in the ACP VRF that
has the ACP address assigned to it. See Section 6.13.5.1.
ACP network: The ACP network comprises all the nodes that have
access to the ACP. It is the set of active and transitively
connected nodes of an ACP domain plus all nodes that get access to
the ACP of that domain via ACP edge nodes.
ACP (ULA) prefix(es): The /48 IPv6 address prefixes used across the
ACP. In the normal or simple case, the ACP has one Unique Local
Address (ULA) prefix, see Section 6.11. The ACP routing table may
include multiple ULA prefixes if the rsub option is used to create
addresses from more than one ULA prefix. See Section 6.2.2. The
ACP may also include non-ULA prefixes if those are configured on
ACP connect interfaces. See Section 8.1.1.
ACP secure channel: A channel authenticated via ACP certificates
providing integrity protection and confidentiality through
encryption. These channels are established between (normally)
adjacent ACP nodes to carry ACP VRF traffic in-band over the same
links and paths as data plane traffic but isolate it from the data
plane traffic and secure it.
ACP secure channel protocol: The protocol used to build an ACP
secure channel, e.g., Internet Key Exchange Protocol version 2
(IKEv2) with IPsec or DTLS.
ACP virtual interface: An interface in the ACP VRF mapped to one or
more ACP secure channels. See Section 6.13.5.
acp-node-name field: An information field in the ACP certificate in
which the following ACP-relevant information is encoded: the ACP
domain name, the ACP IPv6 address of the node, and optional
additional role attributes about the node.
AN: Autonomic Network. A network according to [RFC8993]. Its main
components are ANI, autonomic functions, and Intent.
(AN) Domain Name: An FQDN (Fully Qualified Domain Name) in the acp-
node-name of the domain certificate. See Section 6.2.2.
ANI (nodes/network): Autonomic Network Infrastructure. The ANI is
the infrastructure to enable Autonomic Networks. It includes ACP,
BRSKI, and GRASP. Every Autonomic Network includes the ANI, but
not every ANI network needs to include autonomic functions beyond
the ANI (nor Intent). An ANI network without further autonomic
functions can, for example, support secure zero-touch (automated)
bootstrap and stable connectivity for SDN networks, see [RFC8368].
ANIMA: Autonomic Networking Integrated Model and Approach. ACP,
BRSKI, and GRASP are specifications of the IETF ANIMA Working
Group.
ASA: Autonomic Service Agent. Autonomic software modules running on
an ANI device. The components making up the ANI (BRSKI, ACP, and
GRASP) are also described as ASAs.
autonomic function: A function and/or service in an Autonomic
Network (AN) composed of one or more ASAs across one or more ANI
nodes.
BRSKI: Bootstrapping Remote Secure Key Infrastructure [RFC8995]. A
protocol extending EST to enable secure zero-touch bootstrap in
conjunction with ACP. ANI nodes use ACP, BRSKI, and GRASP.
CA: Certification Authority. An entity that issues digital
certificates. A CA uses its private key to sign the certificates
it issues. Relying parties use the public key in the CA
certificate to validate the signature.
CRL: Certificate Revocation List. A list of revoked certificates is
required to revoke certificates before their lifetime expires.
data plane: The counterpoint to the ACP VRF in an ACP node: the
forwarding of user traffic in non-autonomous nodes and/or networks
and also any non-autonomous control and/or management plane
functions. In a fully Autonomic Network node, the data plane is
managed autonomically via autonomic functions and Intent. See
Section 1 for more details.
device: A physical system or physical node.
enrollment: The process by which a node authenticates itself to a
network with an initial identity, which is often called an Initial
Device IDentity (IDevID) certificate, and acquires from the
network a network-specific identity, which is often called an
LDevID certificate, and certificates of one or more trust
anchor(s). In the ACP, the LDevID certificate is called the ACP
certificate.
EST: Enrollment over Secure Transport [RFC7030]. IETF Standards
Track protocol for enrollment of a node with an LDevID
certificate. BRSKI is based on EST.
GRASP: GeneRic Autonomic Signaling Protocol. An extensible
signaling protocol required by the ACP for ACP neighbor discovery.
The ACP also provides the "security and transport substrate" for
the "ACP instance of GRASP". This instance of GRASP runs across
the ACP secure channels to support BRSKI and other NOC and/or OAM
or autonomic functions. See [RFC8990].
IDevID: An Initial Device IDentity X.509 certificate installed by
the vendor on new equipment. The IDevID certificate contains
information that establishes the identity of the node in the
context of its vendor and/or manufacturer such as device model
and/or type and serial number. See [AR8021]. The IDevID
certificate cannot be used as a node identifier for the ACP
because they are not provisioned by the owner of the network, so
they can not directly indicate an ACP domain they belong to.
in-band (as in management or signaling): In-band management traffic
and/or control plane signaling uses the same network resources
such as routers and/or switches and network links that it manages
and/or controls. In-band is the standard management and signaling
mechanism in IP networks. Compared to out-of-band, the in-band
mechanism requires no additional physical resources, but it
introduces potentially circular dependencies for its correct
operations. See Section 1.
Intent: The policy language of an Autonomic Network according to
[RFC8993].
Loopback interface: See ACP loopback interface.
LDevID: A Local Device IDentity is an X.509 certificate installed
during enrollment. The domain certificate used by the ACP is an
LDevID certificate. See [AR8021].
management: Used in this document as another word for OAM.
MASA (service): Manufacturer Authorized Signing Authority. A vendor
and/or manufacturer or delegated cloud service on the Internet
used as part of the BRSKI protocol.
MIC: Manufacturer Installed Certificate. A synonym for an IDevID in
referenced materials. This term is not used in this document.
native interface: Interfaces existing on a node without
configuration of the already running node. On physical nodes,
these are usually physical interfaces; on virtual nodes, their
equivalent.
NOC: Network Operations Center.
node: A system supporting the ACP according to this document. A
node can be virtual or physical. Physical nodes are called
devices.
Node-ID: The identifier of an ACP node inside that ACP. It is
either the last 64 bits (see Section 6.11.3) or 78 bits (see
Section 6.11.5) of the ACP address.
OAM: Operations, Administration, and Management. Includes network
monitoring.
Operational Technology (OT): "The hardware and software dedicated to
detecting or causing changes in physical processes through direct
monitoring and/or control of physical devices such as valves,
pumps, etc." [OP-TECH]. In most cases today, OT networks are
well separated from Information Technology (IT) networks.
out-of-band (management) network: An out-of-band network is a
secondary network used to manage a primary network. The equipment
of the primary network is connected to the out-of-band network via
dedicated management ports on the primary network equipment.
Serial (console) management ports were historically most common;
however, higher-end network equipment now also has Ethernet ports
dedicated only to management. An out-of-band network provides
management access to the primary network independent of the
configuration state of the primary network. See Section 1.
out-of-band network, virtual: The ACP can be called a virtual out-
of-band network for management and control because it attempts to
provide the benefits of a (physical) out-of-band network even
though it is physically carried in-band. See Section 1.
root CA: root Certification Authority. A CA for which the root CA
key update procedures of [RFC7030], Section 4.4, can be applied.
RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks. The
routing protocol used in the ACP. See [RFC6550].
registrar (ACP, ANI/BRSKI): An ACP registrar is an entity (software
and/or person) that orchestrates the enrollment of ACP nodes with
the ACP certificate. ANI nodes use BRSKI, so ANI registrars are
also called BRSKI registrars. For non-ANI ACP nodes, the
registrar mechanisms are not defined in this document. See
Section 6.11.7. Renewal and other maintenance (such as
revocation) of ACP certificates may be performed by entities other
than registrars. EST must be supported for ACP certificate
renewal (see Section 6.2.5). BRSKI is an extension of EST, so
ANI/BRSKI registrars can easily support ACP domain certificate
renewal in addition to initial enrollment.
RPI: RPL Packet Information. Network extension headers for use with
RPL. Not used with RPL in the ACP. See Section 6.12.1.13.
RPL: Routing Protocol for Low-Power and Lossy Networks. The routing
protocol used in the ACP. See Section 6.12.
sUDI: secured Unique Device Identifier. This is a synonym of IDevID
in referenced material. This term is not used in this document.
TA: Trust Anchor. A TA is an entity that is trusted for the purpose
of certificate validation. TA information such as self-signed
certificate(s) of the TA is configured into the ACP node as part
of enrollment. See [RFC5280], Section 6.1.1.
UDI: Unique Device Identifier. In the context of this document,
unsecured identity information of a node typically consists of at
least a device model and/or type and a serial number, often in a
vendor-specific format. See sUDI and LDevID.
ULA (Global ID prefix): A Unique Local Address is an IPv6 address in
the block fc00::/7, defined in "Unique Local IPv6 Unicast
Addresses" [RFC4193]. ULA is the IPv6 successor of the IPv4
private address space ("Address Allocation for Private Internets"
[RFC1918]). ULAs have important differences over IPv4 private
addresses that are beneficial for and exploited by the ACP, such
as the locally assigned Global ID prefix, which is the first 48
bits of a ULA address [RFC4193], Section 3.2.1. In this document,
this prefix is abbreviated as "ULA prefix".
(ACP) VRF: The ACP is modeled in this document as a Virtual Routing
and Forwarding instance. This means that it is based on a
"virtual router" consisting of a separate IPv6 forwarding table to
which the ACP virtual interfaces are attached and an associated
IPv6 routing table separate from the data plane. Unlike the VRFs
on MPLS/VPN Provider Edge ("BGP/MPLS IP Virtual Private Networks
(VPNs)" [RFC4364]) or LISP xTR ("The Locator/ID Separation
Protocol (LISP)" [RFC6830]), the ACP VRF does not have any special
"core facing" functionality or routing and/or mapping protocols
shared across multiple VRFs. In vendor products, a VRF such as
the ACP VRF may also be referred to as a VRF-lite.
(ACP) Zone: An ACP zone is a set of ACP nodes using the same zone
field value in their ACP address according to Section 6.11.3.
Zones are a mechanism to support structured addressing of ACP
addresses within the same /48 ULA prefix.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Use Cases for an Autonomic Control Plane (Informative)
This section summarizes the use cases that are intended to be
supported by an ACP. To understand how these are derived from and
relate to the larger set of use cases for Autonomic Networks, please
refer to "Autonomic Networking Use Case for Distributed Detection of
Service Level Agreement (SLA) Violations" [RFC8316].
3.1. An Infrastructure for Autonomic Functions
Autonomic functions need a stable infrastructure to run on, and all
autonomic functions should use the same infrastructure to minimize
the complexity of the network. In this way, there is only need for a
single discovery mechanism, a single security mechanism, and single
instances of other processes that distributed functions require.
3.2. Secure Bootstrap over an Unconfigured Network
Today, bootstrapping a new node typically requires all nodes between
a controlling node such as an SDN controller (see [RFC7426]) and the
new node to be completely and correctly addressed, configured, and
secured. Bootstrapping and configuration of a network happens in
rings around the controller -- configuring each ring of devices
before the next one can be bootstrapped. Without console access (for
example, through an out-of-band network), it is not possible today to
make devices securely reachable before having configured the entire
network leading up to them.
With the ACP, secure bootstrap of new devices and whole new networks
can happen without requiring any configuration of unconfigured
devices along the path. As long as all devices along the path
support ACP and a zero-touch bootstrap mechanism such as BRSKI, the
ACP across a whole network of unconfigured devices can be brought up
without operator and/or provisioning intervention. The ACP also
offers additional security for any bootstrap mechanism because it can
provide the encrypted discovery (via ACP GRASP) of registrars or
other bootstrap servers by bootstrap proxies connecting to nodes that
are to be bootstrapped. The ACP encryption hides the identities of
the communicating entities (pledge and registrar), making it more
difficult to learn which network node might be attackable. The ACP
certificate can also be used to end-to-end encrypt the bootstrap
communication between such proxies and server. Note that
bootstrapping here includes not only the first step that can be
provided by BRSKI (secure keys), but also later stages where
configuration is bootstrapped.
3.3. Permanent Reachability Independent of the Data Plane
Today, most critical control plane protocols and OAM protocols use
the data plane of the network. This leads to often undesirable
dependencies between the control and OAM plane on one side and the
data plane on the other: only if the forwarding and control plane of
the data plane are configured correctly, will the data plane and the
OAM and/or control plane work as expected.
Data plane connectivity can be affected by errors and faults.
Examples include misconfigurations that make AAA (Authentication,
Authorization, and Accounting) servers unreachable or that can lock
an administrator out of a device; routing or addressing issues can
make a device unreachable; and shutting down interfaces over which a
current management session is running can lock an administrator
irreversibly out of the device. Traditionally only out-of-band
access via a serial console or Ethernet management port can help
recover from such issues.
Data plane dependencies also affect applications in a NOC such as SDN
controller applications: certain network changes are hard to
implement today because the change itself may affect reachability of
the devices. Examples include address or mask changes, routing
changes, or security policies. Today such changes require precise,
hop-by-hop planning.
Note that specific control plane functions for the data plane often
depend on the ability to forward their packets via the data plane:
sending aliveness and routing protocol signaling packets across the
data plane to verify reachability, using IPv4 signaling packets for
IPv4 routing and IPv6 signaling packets for IPv6 routing.
Assuming appropriate implementation (see Section 6.13.2 for more
details), the ACP provides reachability that is independent of the
data plane. This allows the control plane and OAM plane to operate
more robustly:
* For management plane protocols, the ACP provides the functionality
of a Virtual out-of-Band (VooB) channel, by providing connectivity
to all nodes regardless of their data plane configuration, and
routing and forwarding tables.
* For control plane protocols, the ACP allows their operation even
when the data plane is temporarily faulty, or during transitional
events, such as routing changes, which may affect the control
plane at least temporarily. This is specifically important for
autonomic service agents, which could affect data plane
connectivity.
The document "Using Autonomic Control Plane for Stable Connectivity
of Network OAM" [RFC8368] explains this use case for the ACP in
significantly more detail and explains how the ACP can be used in
practical network operations.
4. Requirements (Informative)
The following requirements were identified for the design of the ACP
based on the above use cases (Section 3). These requirements are
informative. The ACP as specified in the normative parts of this
document is meeting or exceeding these use case requirements:
ACP1: The ACP should provide robust connectivity: as far as
possible, it should be independent of configured
addressing, configuration, and routing. Requirements 2 and
3 build on this requirement, but they also have value on
their own.
ACP2: The ACP must have a separate address space from the data
plane. This separate address space provides traceability,
ease of debugging, separation from data plane, and
infrastructure security (filtering based on known address
space).
ACP3: The ACP must use an autonomically managed address space.
An autonomically managed address space provides ease of
bootstrap and setup ("autonomic"), and robustness (the
administrator cannot break network easily). This document
uses ULA for this purpose, see [RFC4193].
ACP4: The ACP must be generic, that is, it must be usable by all
the functions and protocols of the ANI. Clients of the ACP
must not be tied to a particular application or transport
protocol.
ACP5: The ACP must provide security: messages coming through the
ACP must be authenticated to be from a trusted node, and it
is very strongly recommended that they be encrypted.
The explanation for ACP4 is as follows: in a fully Autonomic Network
(AN), all newly written ASAs could potentially communicate with each
other exclusively via GRASP, and if that were the only requirement
for the ACP, it would not need to provide IPv6-layer connectivity
between nodes, but only GRASP connectivity. Nevertheless, because
ACP also intends to support non-autonomous networks, it is crucial to
support IPv6-layer connectivity across the ACP to support any
transport-layer and application-layer protocols.
The ACP operates hop-by-hop because this interaction can be built on
IPv6 link-local addressing, which is autonomic, and has no dependency
on configuration (requirement ACP1). It may be necessary to have ACP
connectivity across non-ACP nodes, for example, to link ACP nodes
over the general Internet. This is possible, but it introduces a
dependency on stable and/or resilient routing over the non-ACP hops
(see Section 8.2).
5. Overview (Informative)
When a node has an ACP certificate (see Section 6.2.1) and is enabled
to bring up the ACP (see Section 9.3.5), it will create its ACP
without any configuration as follows. For details, see Section 6 and
following sections:
1. The node creates a VRF instance or a similar virtual context for
the ACP.
2. The node assigns its ULA IPv6 address (prefix) (see
Section 6.11), which is learned from the acp-node-name (see
Section 6.2.2) of its ACP certificate (see Section 6.2.1), to an
ACP loopback interface (see Section 6.11) and connects this
interface to the ACP VRF.
3. The node establishes a list of candidate peer adjacencies and
candidate channel types to try for the adjacency. This is
automatic for all candidate link-local adjacencies (see
Section 6.4) across all native interfaces (see Section 9.3.4).
If a candidate peer is discovered via multiple interfaces, this
will result in one adjacency per interface. If the ACP node has
multiple interfaces connecting to the same subnet across which it
is also operating as an L2 switch in the data plane, it employs
methods for ACP with L2 switching, see Section 7.
4. For each entry in the candidate adjacency list, the node
negotiates a secure tunnel using the candidate channel types.
See Section 6.6.
5. The node authenticates the peer node during secure channel setup
and authorizes it to become part of the ACP according to
Section 6.2.3.
6. Unsuccessful authentication of a candidate peer results in
throttled connection retries for as long as the candidate peer is
discoverable. See Section 6.7.
7. Each successfully established secure channel is mapped to an ACP
virtual interface, which is placed into the ACP VRF. See
Section 6.13.5.2.
8. Each node runs a lightweight routing protocol (see Section 6.12)
to announce reachability of the ACP loopback address (or prefix)
across the ACP.
9. This completes the creation of the ACP with hop-by-hop secure
tunnels, auto-addressing, and auto-routing. The node is now an
ACP node with a running ACP.
Note:
* None of the above operations (except the following explicitly
configured ones) are reflected in the configuration of the node.
* Non-ACP network management systems (NMS) or SDN controllers have
to be explicitly configured for connection to the ACP.
* Additional candidate peer adjacencies for ACP connections across
non-ACP Layer 3 clouds requires explicit configuration. See
Section 8.2.
Figure 1 illustrates the ACP.
ACP Node 1 ACP Node 2
................... ...................
secure . . secure . . secure
channel: +-----------+ : channel : +-----------+ : channel
..--------| ACP VRF |---------------------| ACP VRF |---------..
: / \ / \ <--routing--> / \ / \ :
: \ / \ / \ / \ / :
..--------| loopback |---------------------| loopback |---------..
: | interface | : : | interface | :
: +-----------+ : : +-----------+ :
: : : :
: Data Plane :...............: Data Plane :
: : link : :
:.................: :.................:
Figure 1: ACP VRF and Secure Channels
The resulting overlay network is normally based exclusively on hop-
by-hop tunnels. This is because addressing used on links is IPv6
link-local addressing, which does not require any prior setup. In
this way, the ACP can be built even if there is no configuration on
the node, or if the data plane has issues such as addressing or
routing problems.
6. Self-Creation of an Autonomic Control Plane (ACP) (Normative)
This section specifies the components and steps to set up an ACP.
The ACP is automatically self-creating, which makes it
"indestructible" against most changes to the data plane, including
misconfigurations of routing, addressing, NAT, firewall, or any other
traffic policy filters that would inadvertently or otherwise
unavoidably also impact the management plane traffic, such as the
actual operator command-line interface (CLI) session or controller
NETCONF session through which the configuration changes to the data
plane are executed.
Physical misconfiguration of wiring between ACP nodes will also not
break the ACP. As long as there is a transitive physical path
between ACP nodes, the ACP should be able to recover given that it
automatically operates across all interfaces of the ACP nodes and
automatically determines paths between them.
Attacks against the network via incorrect routing or addressing
information for the data plane will not impact the ACP. Even
impaired ACP nodes will have a significantly reduced attack surface
against malicious misconfiguration because only very limited ACP or
interface up/down configuration can affect the ACP, and depending on
their specific designs, these types of attacks could also be
eliminated. See more in Section 9.3 and Section 11.
An ACP node can be a router, switch, controller, NMS host, or any
other IPv6-capable node. Initially, it MUST have its ACP
certificate, as well as an (empty) ACP adjacency table (described in
Section 6.3). It then can start to discover ACP neighbors and build
the ACP. This is described step by step in the following sections.
6.1. Requirements for the Use of Transport Layer Security (TLS)
The following requirements apply to TLS that is required or used by
ACP components. Applicable ACP components include ACP certificate
maintenance via EST (see Section 6.2.5), TLS connections for CRL
Distribution Point (CRLDP) or Online Certificate Status Protocol
(OCSP) responder (if used, see Section 6.2.3), and ACP GRASP (see
Section 6.9.2). On ANI nodes, these requirements also apply to
BRSKI.
TLS MUST comply with "Recommendations for Secure Use of Transport
Layer Security (TLS) and Datagram Transport Layer Security (DTLS)"
[RFC7525] except that TLS 1.2 ("The Transport Layer Security (TLS)
Protocol Version 1.2" [RFC5246]) is REQUIRED and that older versions
of TLS MUST NOT be used. TLS 1.3 ("The Transport Layer Security
(TLS) Protocol Version 1.3" [RFC8446]) SHOULD be supported. The
choice for TLS 1.2 as the lowest common denominator for the ACP is
based on the currently expected and most likely availability across
the wide range of candidate ACP node types, potentially with non-
agile operating system TCP/IP stacks.
TLS MUST offer TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 and
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 and MUST NOT offer options
with less than 256-bit symmetric key strength or hash strength of
less than 384 bits. When TLS 1.3 is supported,
TLS_AES_256_GCM_SHA384 MUST be offered and
TLS_CHACHA20_POLY1305_SHA256 MAY be offered.
TLS MUST also include the "Supported Elliptic Curves" extension, and
it MUST support the NIST P-256 (secp256r1(22)) and P-384
(secp384r1(24)) curves "Elliptic Curve Cryptography (ECC) Cipher
Suites for Transport Layer Security (TLS) Versions 1.2 and Earlier"
[RFC8422]. In addition, TLS 1.2 clients SHOULD send an
ec_point_format extension with a single element, "uncompressed".
6.2. ACP Domain, Certificate, and Network
The ACP relies on group security. An ACP domain is a group of nodes
that trust each other to participate in ACP operations such as
creating ACP secure channels in an autonomous, peer-to-peer fashion
between ACP domain members via protocols such as IPsec. To
authenticate and authorize another ACP member node with access to the
ACP domain, each ACP member requires keying material: an ACP node
MUST have an LDevID certificate and information about one or more TAs
as required for the ACP domain membership check (Section 6.2.3).
Manual keying via shared secrets is not usable for an ACP domain
because it would require a single shared secret across all current
and future ACP domain members to meet the expectation of autonomous,
peer-to-peer establishment of ACP secure channels between any ACP
domain members. Such a single shared secret would be an unacceptable
security weakness. Asymmetric keying material (public keys) without
certificates does not provide the mechanism to authenticate ACP
domain membership in an autonomous, peer-to-peer fashion for current
and future ACP domain members.
The LDevID certificate is henceforth called the ACP certificate. The
TA is the CA root certificate of the ACP domain.
The ACP does not mandate specific mechanisms by which this keying
material is provisioned into the ACP node. It only requires that the
certificate comply with Section 6.2.1, specifically that it have the
acp-node-name as specified in Section 6.2.2 in its domain certificate
as well as those of candidate ACP peers. See Appendix A.2 for more
information about enrollment or provisioning options.
This document uses the term ACP in many places where the Autonomic
Networking reference documents [RFC7575] and [RFC8993] use the word
autonomic. This is done because those reference documents consider
(only) fully Autonomic Networks and nodes, but the support of ACP
does not require the support for other components of Autonomic
Networks except for the reliance on GRASP and the providing of
security and transport for GRASP. Therefore, the word autonomic
might be misleading to operators interested in only the ACP.
[RFC7575] defines the term "autonomic domain" as a collection of
autonomic nodes. ACP nodes do not need to be fully autonomic, but
when they are, then the ACP domain is an autonomic domain. Likewise,
[RFC8993] defines the term "domain certificate" as the certificate
used in an autonomic domain. The ACP certificate is that domain
certificate when ACP nodes are (fully) autonomic nodes. Finally,
this document uses the term ACP network to refer to the network
created by active ACP nodes in an ACP domain. The ACP network itself
can extend beyond ACP nodes through the mechanisms described in
Section 8.1.
6.2.1. ACP Certificates
ACP certificates MUST be [RFC5280] compliant X.509 v3 [X.509]
certificates.
ACP nodes MUST support handling ACP certificates, TA certificates,
and certificate chain certificates (henceforth just called
certificates in this section) with RSA public keys and certificates
with Elliptic Curve Cryptography (ECC) public keys.
ACP nodes MUST NOT support certificates with RSA public keys of less
than a 2048-bit modulus or curves with group order of less than 256
bits. They MUST support certificates with RSA public keys with
2048-bit modulus and MAY support longer RSA keys. They MUST support
certificates with ECC public keys using NIST P-256 curves and SHOULD
support P-384 and P-521 curves.
ACP nodes MUST NOT support certificates with RSA public keys whose
modulus is less than 2048 bits, or certificates whose ECC public keys
are in groups whose order is less than 256 bits. RSA signing
certificates with 2048-bit public keys MUST be supported, and such
certificates with longer public keys MAY be supported. ECDSA
certificates using the NIST P-256 curve MUST be supported, and such
certificates using the P-384 and P-521 curves SHOULD be supported.
ACP nodes MUST support RSA certificates that are signed by RSA
signatures over the SHA-256 digest of the contents and SHOULD
additionally support SHA-384 and SHA-512 digests in such signatures.
The same requirements for digest usage in certificate signatures
apply to Elliptic Curve Digital Signature Algorithm (ECDSA)
certificates, and additionally, ACP nodes MUST support ECDSA
signatures on ECDSA certificates.
The ACP certificate SHOULD use an RSA key and an RSA signature when
the ACP certificate is intended to be used not only for ACP
authentication but also for other purposes. The ACP certificate MAY
use an ECC key and an ECDSA signature if the ACP certificate is only
used for ACP and ANI authentication and authorization.
Any secure channel protocols used for the ACP as specified in this
document or extensions of this document MUST therefore support
authentication (e.g., signing), starting with these types of
certificates. See [RFC8422] for more information.
The reason for these choices are as follows: as of 2020, RSA is still
more widely used than ECC, therefore the MUST-level requirements for
RSA. ECC offers equivalent security at (logarithmically) shorter key
lengths (see [RFC8422]). This can be beneficial especially in the
presence of constrained bandwidth or constrained nodes in an ACP/ANI
network. Some ACP functions such as GRASP peer-to-peer across the
ACP require end-to-end/any-to-any authentication and authorization,
therefore ECC can only reliably be used in the ACP when it MUST be
supported on all ACP nodes. RSA signatures are mandatory to be
supported also for ECC certificates because the CAs themselves may
not support ECC yet.
The ACP certificate SHOULD be used for any authentication between
nodes with ACP domain certificates (ACP nodes and NOC nodes) where a
required authorization condition is ACP domain membership, such as
ACP node to NOC/OAM end-to-end security and ASA to ASA end-to-end
security. Section 6.2.3 defines this "ACP domain membership check".
The uses of this check that are standardized in this document are for
the establishment of hop-by-hop ACP secure channels (Section 6.8) and
for ACP GRASP (Section 6.9.2) end to end via TLS.
The ACP domain membership check requires a minimum number of elements
in a certificate as described in Section 6.2.3. The identity of a
node in the ACP is carried via the acp-node-name as defined in
Section 6.2.2.
To support Elliptic Curve Diffie-Hellman (ECDH) directly with the key
in the ACP certificate, ACP certificates with ECC keys need to
indicate that they are ECDH capable: if the X.509 v3 keyUsage
extension is present, the keyAgreement bit must then be set. Note
that this option is not required for any of the required ciphersuites
in this document and may not be supported by all CAs.
Any other fields of the ACP certificate are to be populated as
required by [RFC5280]. As long as they are compliant with [RFC5280],
any other field of an ACP certificate can be set as desired by the
operator of the ACP domain through the appropriate ACP registrar and/
or ACP CA procedures. For example, other fields may be required for
purposes other than those that the ACP certificate is intended to be
used for (such as elements of a SubjectName).
For further certificate details, ACP certificates may follow the
recommendations from [CABFORUM].
For diagnostic and other operational purposes, it is beneficial to
copy the device-identifying fields of the node's IDevID certificate
into the ACP certificate, such as the "serialNumber" attribute
([X.520], Section 6.2.9) in the subject field distinguished name
encoding. Note that this is not the certificate serial-number. See
also [RFC8995], Section 2.3.1. This can be done, for example, if it
would be acceptable for the device's "serialNumber" to be signaled
via the Link Layer Discovery Protocol [LLDP] because, like LLDP-
signaled information, the ACP certificate information can be
retrieved by neighboring nodes without further authentication and can
be used either for beneficial diagnostics or for malicious attacks.
Retrieval of the ACP certificate is possible via a (failing) attempt
to set up an ACP secure channel, and the "serialNumber" usually
contains device type information that may help to more quickly
determine working exploits/attacks against the device.
Note that there is no intention to constrain authorization within the
ACP or Autonomic Networks using the ACP to just the ACP domain
membership check as defined in this document. It can be extended or
modified with additional requirements. Such future authorizations
can use and require additional elements in certificates or policies
or even additional certificates. See Section 6.2.5 for the
additional check against the id-kp-cmcRA extended key usage attribute
("Certificate Management over CMS (CMC) Updates" [RFC6402]), and see
Appendix A.9.5 for possible future extensions.
6.2.2. ACP Certificate AcpNodeName
acp-node-name = local-part "@" acp-domain-name
local-part = [ acp-address ] [ "+" rsub extensions ]
acp-address = 32HEXDIG / "0" ; HEXDIG as of [RFC5234], Appendix B.1
rsub = [ <subdomain> ] ; <subdomain> as of [RFC1034], Section 3.5
acp-domain-name = <domain> ; as of [RFC1034], Section 3.5
extensions = *( "+" extension )
extension = 1*etext ; future standard definition.
etext = ALPHA / DIGIT / ; Printable US-ASCII
"!" / "#" / "$" / "%" / "&" / "'" /
"*" / "-" / "/" / "=" / "?" / "^" /
"_" / "`" / "{" / "|" / "}" / "~"
routing-subdomain = [ rsub "." ] acp-domain-name
Figure 2: ACP Node Name ABNF
Example:
Given an ACP address of fd89:b714:f3db:0:200:0:6400:0000, an ACP
domain name of acp.example.com, and an rsub extension of
area51.research, then this results in the following:
acp-node-name = fd89b714f3db00000200000064000000
[email protected]
acp-domain-name = acp.example.com
routing-subdomain = area51.research.acp.example.com
The acp-node-name in Figure 2 is the ABNF definition ("Augmented BNF
for Syntax Specifications: ABNF" [RFC5234]) of the ACP Node Name. An
ACP certificate MUST carry this information. It MUST contain an
otherName field in the X.509 Subject Alternative Name extension, and
the otherName MUST contain an AcpNodeName as described in
Section 6.2.2.
Nodes complying with this specification MUST be able to receive their
ACP address through the domain certificate, in which case their own
ACP certificate MUST have a 32HEXDIG acp-address field. The acp-
address field is case insensitive because ABNF HEXDIG is. It is
recommended to encode acp-address with lowercase letters. Nodes
complying with this specification MUST also be able to authenticate
nodes as ACP domain members or ACP secure channel peers when they
have a zero-value acp-address field and as ACP domain members (but
not as ACP secure channel peers) when the acp-address field is
omitted from their AcpNodeName. See Section 6.2.3.
The acp-domain-name is used to indicate the ACP domain across which
ACP nodes authenticate and authorize each other, for example, to
build ACP secure channels to each other, see Section 6.2.3. The acp-
domain-name SHOULD be the FQDN of an Internet domain owned by the
network administration of the ACP and ideally reserved to only be
used for the ACP. In this specification, it serves as a name for the
ACP that ideally is globally unique. When acp-domain-name is a
globally unique name, collision of ACP addresses across different ACP
domains can only happen due to ULA hash collisions (see
Section 6.11.2). Using different acp-domain-names, operators can
distinguish multiple ACPs even when using the same TA.
To keep the encoding simple, there is no consideration for
internationalized acp-domain-names. The acp-node-name is not
intended for end-user consumption. There is no protection against an
operator picking any domain name for an ACP whether or not the
operator can claim to own the domain name. Instead, the domain name
only serves as a hash seed for the ULA and for diagnostics for the
operator. Therefore, any operator owning only an internationalized
domain name should be able to pick an equivalently unique 7-bit ASCII
acp-domain-name string representing the internationalized domain
name.
The routing-subdomain is a string that can be constructed from the
acp-node-name, and it is used in the hash creation of the ULA (see
Section 6.11.2). The presence of the rsub component allows a single
ACP domain to employ multiple /48 ULA prefixes. See Appendix A.6 for
example use cases.
The optional extensions field is used for future standardized
extensions to this specification. It MUST be ignored if present and
not understood.
The following points explain and justify the encoding choices
described:
1. Formatting notes:
1.1 The rsub component needs to be in the local-part: if the
format just had routing-subdomain as the domain part of the
acp-node-name, rsub and acp-domain-name could not be
separated from each other to determine in the ACP domain
membership check which part is the acp-domain-name and which
is solely for creating a different ULA prefix.
1.2 If both acp-address and rsub are omitted from AcpNodeName,
the local-part will have the format "++extension(s)". The
two plus characters are necessary so the node can
unambiguously parse that both acp-address and rsub are
omitted.
2. The encoding of the ACP domain name and ACP address as described
in this section is used for the following reasons:
2.1 The acp-node-name is the identifier of a node's ACP. It
includes the necessary components to identify a node's ACP
both from within the ACP as well as from the outside of the
ACP.
2.2 For manual and/or automated diagnostics and backend
management of devices and ACPs, it is necessary to have an
easily human-readable and software-parsable standard, single
string representation of the information in the acp-node-
name. For example, inventory or other backend systems can
always identify an entity by one unique string field but not
by a combination of multiple fields, which would be
necessary if there were no single string representation.
2.3 If the encoding was not such a string, it would be necessary
to define a second standard encoding to provide this format
(standard string encoding) for operator consumption.
2.4 Addresses of the form <local>@<domain> have become the
preferred format for identifiers of entities in many
systems, including the majority of user identifiers in web
or mobile applications such as multi-domain single-sign-on
systems.
3. Compatibilities:
3.1 It should be possible to use the ACP certificate as an
LDevID certificate on the system for uses besides the ACP.
Therefore, the information element required for the ACP
should be encoded so that it minimizes the possibility of
creating incompatibilities with other such uses. The
attributes of the subject field, for example, are often used
in non-ACP applications and therefore should not be occupied
by new ACP values.
3.2 The element should not require additional ASN.1 encoding
and/or decoding because libraries for accessing certificate
information, especially for embedded devices, may not
support extended ASN.1 decoding beyond predefined, mandatory
fields. subjectAltName / otherName is already used with a
single string parameter for several otherNames (see
"Extensible Messaging and Presence Protocol (XMPP): Core"
[RFC6120], "Dynamic Peer Discovery for RADIUS/TLS and
RADIUS/DTLS Based on the Network Access Identifier (NAI)"
[RFC7585], "Internet X.509 Public Key Infrastructure Subject
Alternative Name for Expression of Service Name" [RFC4985],
"Internationalized Email Addresses in X.509 Certificates"
[RFC8398]).
3.3 The element required for the ACP should minimize the risk of
being misinterpreted by other uses of the LDevID
certificate. It also must not be misinterpreted as an email
address, hence the use of the otherName / rfc822Name option
in the certificate would be inappropriate.
See Section 4.2.1.6 of [RFC5280] for details on the subjectAltName
field.
6.2.2.1. AcpNodeName ASN.1 Module
The following ASN.1 module normatively specifies the AcpNodeName
structure. This specification uses the ASN.1 definitions from "New
ASN.1 Modules for the Public Key Infrastructure Using X.509 (PKIX)"
[RFC5912] with the 2002 ASN.1 notation used in that document.
[RFC5912] updates normative documents using older ASN.1 notation.
ANIMA-ACP-2020
{ iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-anima-acpnodename-2020(97) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
OTHER-NAME
FROM PKIX1Implicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-implicit-02(59) }
id-pkix
FROM PKIX1Explicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-explicit-02(51) } ;
id-on OBJECT IDENTIFIER ::= { id-pkix 8 }
AcpNodeNameOtherNames OTHER-NAME ::= { on-AcpNodeName, ... }
on-AcpNodeName OTHER-NAME ::= {
AcpNodeName IDENTIFIED BY id-on-AcpNodeName
}
id-on-AcpNodeName OBJECT IDENTIFIER ::= { id-on 10 }
AcpNodeName ::= IA5String (SIZE (1..MAX))
-- AcpNodeName as specified in this document carries the
-- acp-node-name as specified in the ABNF in Section 6.2.2
END
Figure 3: AcpNodeName ASN.1 Module
6.2.3. ACP Domain Membership Check
The following points constitute the ACP domain membership check of a
candidate peer via its certificate:
1. The peer has proved ownership of the private key associated with
the certificate's public key. This check is performed by the
security association protocol used, for example, Section 2.15 of
"Internet Key Exchange Protocol Version 2 (IKEv2)" [RFC7296].
2. The peer's certificate passes certificate path validation as
defined in [RFC5280], Section 6, against one of the TAs
associated with the ACP node's ACP certificate (see
Section 6.2.4). This includes verification of the validity
(lifetime) of the certificates in the path.
3. If the peer's certificate indicates a CRLDP ([RFC5280],
Section 4.2.1.13) or OCSP responder ([RFC5280], Section 4.2.2.1),
then the peer's certificate MUST be valid according to those
mechanisms when they are available: an OCSP check for the peer's
certificate across the ACP must succeed, or the peer's
certificate must not be listed in the CRL retrieved from the
CRLDP. These mechanisms are not available when the ACP node has
no ACP or non-ACP connectivity to retrieve a current CRL or has
no access an OCSP responder, and the security association
protocol itself also has no way to communicate the CRL or OCSP
check.
Retries to learn revocation via OCSP or CRL SHOULD be made using
the same backoff as described in Section 6.7. If and when the
ACP node then learns that an ACP peer's certificate is invalid
for which Rule 3 had to be skipped during ACP secure channel
establishment, then the ACP secure channel to that peer MUST be
closed even if this peer is the only connectivity to access CRL/
OCSP. This applies (of course) to all ACP secure channels to
this peer if there are multiple. The ACP secure channel
connection MUST be retried periodically to support the case that
the neighbor acquires a new, valid certificate.
4. The peer's certificate has a syntactically valid acp-node-name
field, and the acp-domain-name in that peer's acp-node-name is
the same as in this ACP node's certificate (lowercase
normalized).
When checking a candidate peer's certificate for the purpose of
establishing an ACP secure channel, one additional check is
performed:
5. The acp-address field of the candidate peer certificate's
AcpNodeName is not omitted but is either 32HEXDIG or 0, according
to Figure 2.
Technically, ACP secure channels can only be built with nodes that
have an acp-address. Rule 5 ensures that this is taken into account
during ACP domain membership check.
Nodes with an omitted acp-address field can only use their ACP domain
certificate for non-ACP secure channel authentication purposes. This
includes, for example, NMS type nodes permitted to communicate into
the ACP via ACP connect (Section 8.1)
The special value "0" in an ACP certificate's acp-address field is
used for nodes that can and should determine their ACP address
through mechanisms other than learning it through the acp-address
field in their ACP certificate. These ACP nodes are permitted to
establish ACP secure channels. Mechanisms for those nodes to
determine their ACP address are outside the scope of this
specification, but this option is defined here so that any ACP nodes
can build ACP secure channels to them according to Rule 5.
The optional rsub field of the AcpNodeName is not relevant to the ACP
domain membership check because it only serves to structure routing
and addressing within an ACP but not to segment mutual authentication
and authorization (hence the name "routing subdomain").
In summary:
* Steps 1 through 4 constitute standard certificate validity
verification and private key authentication as defined by
[RFC5280] and security association protocols (such as IKEv2
[RFC7296]) when leveraging certificates.
* Except for its public key, Steps 1 through 4 do not include the
verification of any preexisting form of a certificate's identity
elements, such as a web server's domain name prefix, which is
often encoded in the certificate common name. Step 5 is an
equivalent step for the AcpNodeName.
* Step 4 constitutes standard CRL and OCSP checks refined for the
case of missing connectivity and limited-functionality security
association protocols.
* Steps 1 through 4 authorize the building of any secure connection
between members of the same ACP domain except for ACP secure
channels.
* Step 5 is the additional verification of the presence of an ACP
address as necessary for ACP secure channels.
* Steps 1 through 5 therefore authorize the building of an ACP
secure channel.
For brevity, the remainder of this document refers to this process
only as authentication instead of as authentication and
authorization.
6.2.3.1. Realtime Clock and Time Validation
An ACP node with a realtime clock in which it has confidence MUST
check the timestamps when performing an ACP domain membership check,
such as checking the certificate validity period in Step 1 and the
respective times in Step 4 for revocation information (e.g.,
signingTimes in Cryptographic Message Syntax (CMS) signatures).
An ACP node without such a realtime clock MAY ignore those timestamp
validation steps if it does not know the current time. Such an ACP
node SHOULD obtain the current time in a secured fashion, such as via
NTP signaled through the ACP. It then ignores timestamp validation
only until the current time is known. In the absence of implementing
a secured mechanism, such an ACP node MAY use a current time learned
in an insecure fashion in the ACP domain membership check.
Current time MAY be learned in an unsecured fashion, for example, via
NTP ("Network Time Protocol Version 4: Protocol and Algorithms
Specification" [RFC5905]) over the same link-local IPv6 addresses
used for the ACP from neighboring ACP nodes. ACP nodes that do
provide unsecured NTP over their link-local addresses SHOULD
primarily run NTP across the ACP and provide NTP time across the ACP
only when they have a trusted time source. Details for such NTP
procedures are beyond the scope of this specification.
Besides the ACP domain membership check, the ACP itself has no
dependency on knowing the current time, but protocols and services
using the ACP, for example, event logging, will likely need to know
the current time.
6.2.4. Trust Anchors (TA)
ACP nodes need TA information according to [RFC5280], Section 6.1.1
(d), typically in the form of one or more certificates of the TA to
perform certificate path validation as required by Section 6.2.3,
Rule 2. TA information MUST be provisioned to an ACP node (together
with its ACP domain certificate) by an ACP registrar during initial
enrollment of a candidate ACP node. ACP nodes MUST also support the
renewal of TA information via EST as described in Section 6.2.5.
The required information about a TA can consist of one or more
certificates as required for dealing with CA certificate renewals as
explained in Section 4.4 of "Internet X.509 Public Key Infrastructure
Certificate Management Protocol (CMP)" [RFC4210]).
A certificate path is a chain of certificates starting at the ACP
certificate (the leaf and/or end entity), followed by zero or more
intermediate CA certificates, and ending with the TA information,
which is typically one or two self-signed certificates of the TA.
The CA that signs the ACP certificate is called the assigning CA. If
there are no intermediate CAs, then the assigning CA is the TA.
Certificate path validation authenticates that the TA associated with
the ACP permits the ACP certificate, either directly or indirectly
via one or more intermediate CA.
Note that different ACP nodes may have different intermediate CAs in
their certificate path and even different TA. The set of TAs for an
ACP domain must be consistent across all ACP members so that any ACP
node can authenticate any other ACP node. The protocols through
which the ACP domain membership check Rules 1 through 3 are performed
need to support the exchange not only of the ACP nodes certificates
but also the exchange of the intermediate TA.
For the ACP domain membership check, ACP nodes MUST support
certificate path validation with zero or one intermediate CA. They
SHOULD support two intermediate CAs and two TAs (to permit migration
from one TA to another TA).
Certificates for an ACP MUST only be given to nodes that are allowed
to be members of that ACP. When the signing CA relies on an ACP
registrar, the CA MUST only sign certificates with acp-node-name
through trusted ACP registrars. In this setup, any existing CA,
unaware of the formatting of acp-node-name, can be used.
These requirements can be achieved by using a TA private to the owner
of the ACP domain or potentially through appropriate contractual
agreements between the involved parties (registrar and CA). Using a
public CA is out of scope of this document.
A single owner can operate multiple, independent ACP domains from the
same set of TAs. Registrars must then know into which ACP a node
needs to be enrolled.
6.2.5. Certificate and Trust Anchor Maintenance
ACP nodes MUST support renewal of their certificate and TA
information via EST and MAY support other mechanisms. See
Section 6.1 for TLS requirements. An ACP network MUST have at least
one ACP node supporting EST server functionality across the ACP so
that EST renewal is usable.
ACP nodes SHOULD remember the GRASP O_IPv6_LOCATOR parameters of the
EST server with which they last renewed their ACP certificate. They
SHOULD provide the ability for these EST server parameters to also be
set by the ACP registrar (see Section 6.11.7) that initially enrolled
the ACP device with its ACP certificate. When BRSKI is used (see
[RFC8995]), the IPv6 locator of the BRSKI registrar from the BRSKI
TLS connection SHOULD be remembered and used for the next renewal via
EST if that registrar also announces itself as an EST server via
GRASP on its ACP address (see Section 6.2.5.1).
The EST server MUST present a certificate that passes the ACP domain
membership check in its TLS connection setup (Section 6.2.3, rules 1
through 4, not rule 5 as this is not for an ACP secure channel
setup). The EST server certificate MUST also contain the id-kp-cmcRA
extended key usage attribute [RFC6402], and the EST client MUST check
its presence.
The additional check against the id-kp-cmcRA extended key usage
extension field ensures that clients do not fall prey to an illicit
EST server. While such illicit EST servers should not be able to
support certificate signing requests (as they are not able to elicit
a signing response from a valid CA), such an illicit EST server would
be able to provide faked CA certificates to EST clients that need to
renew their CA certificates when they expire.
Note that EST servers supporting multiple ACP domains will need to
have a separate certificate for each of these ACP domains and respond
on a different transport address (IPv6 address and/or TCP port).
This is easily automated on the EST server if the CA allows
registrars to request certificates with the id-kp-cmcRA extended
usage extension for themselves.
6.2.5.1. GRASP Objective for EST Server
ACP nodes that are EST servers MUST announce their service in the ACP
via GRASP Flood Synchronization (M_FLOOD) messages. See [RFC8990],
Section 2.8.11 for the definition of this message type and Figure 4
for an example.
[M_FLOOD, 12340815, h'fd89b714f3db0000200000064000001', 210000,
[["SRV.est", 4, 255 ],
[O_IPv6_LOCATOR,
h'fd89b714f3db0000200000064000001', IPPROTO_TCP, 443]]
]
Figure 4: GRASP "SRV.est" Objective Example
The formal definition of the objective in CDDL (see "Concise Data
Definition Language (CDDL): A Notational Convention to Express
Concise Binary Object Representation (CBOR) and JSON Data Structures"
[RFC8610]) is as follows:
flood-message = [M_FLOOD, session-id, initiator, ttl,
+[objective, (locator-option / [])]]
; See example above and explanation
; below for initiator and ttl.
objective = ["SRV.est", objective-flags, loop-count,
objective-value]
objective-flags = sync-only ; As in [RFC8990].
sync-only = 4 ; M_FLOOD only requires synchronization.
loop-count = 255 ; Recommended as there is no mechanism
; to discover network diameter.
objective-value = any ; Reserved for future extensions.
Figure 5: GRASP "SRV.est" Definition
The objective name "SRV.est" indicates that the objective is an EST
server compliant with [RFC7030] because "est" is a registered service
name ("Internet Assigned Numbers Authority (IANA) Procedures for the
Management of the Service Name and Transport Protocol Port Number
Registry" [RFC6335]) for [RFC7030]. The 'objective-value' field MUST
be ignored if present. Backward-compatible extensions to [RFC7030]
MAY be indicated through 'objective-value'. Certificate renewal
options that are incompatible with [RFC7030] MUST use a different
'objective-name'. Unrecognized 'objective-value' fields (or parts
thereof if it is a partially understood structure) MUST be ignored.
The M_FLOOD message MUST be sent periodically. The default SHOULD be
60 seconds; the value SHOULD be operator configurable but SHOULD be
not smaller than 60 seconds. The frequency of sending MUST be such
that the aggregate amount of periodic M_FLOODs from all flooding
sources cause only negligible traffic across the ACP. The time-to-
live (ttl) parameter SHOULD be 3.5 times the period so that up to
three consecutive messages can be dropped before an announcement is
considered expired. In the example above, the ttl is 210000 msec,
that is, 3.5 times 60 seconds. When a service announcer using these
parameters unexpectedly dies immediately after sending the M_FLOOD,
receivers would consider it expired 210 seconds later. When a
receiver tries to connect to this dead service before this timeout,
it will experience a failing connection and use that as an indication
that the service instance is dead and select another instance of the
same service instead (from another GRASP announcement).
The "SRV.est" objective(s) SHOULD only be announced when the ACP node
knows that it can successfully communicate with a CA to perform the
EST renewal and/or rekeying operations for the ACP domain. See also
Section 11.
6.2.5.2. Renewal
When performing renewal, the node SHOULD attempt to connect to the
remembered EST server. If that fails, it SHOULD attempt to connect
to an EST server learned via GRASP. The server with which
certificate renewal succeeds SHOULD be remembered for the next
renewal.
Remembering the last renewal server and preferring it provides
stickiness that can help diagnostics. It also provides some
protection against off-path, compromised ACP members announcing bogus
information into GRASP.
Renewal of certificates SHOULD start after less than 50% of the
domain certificate lifetime so that network operations have ample
time to investigate and resolve any problems that cause a node to not
renew its domain certificate in time, and to allow prolonged periods
of running parts of a network disconnected from any CA.
6.2.5.3. Certificate Revocation Lists (CRLs)
The ACP node SHOULD support revocation through CRL(s) via HTTP from
one or more CRL Distribution Points (CRLDP). The CRLDP(s) MUST be
indicated in the domain certificate when used. If the CRLDP URL uses
an IPv6 address (ULA address when using the addressing rules
specified in this document), the ACP node will connect to the CRLDP
via the ACP. If the CRLDP uses a domain name, the ACP node will
connect to the CRLDP via the data plane.
It is common to use domain names for CRLDP(s), but there is no
requirement for the ACP to support DNS. Any DNS lookup in the data
plane is not only a possible security issue, but it would also not
indicate whether the resolved address is meant to be reachable across
the ACP. Therefore, the use of an IPv6 address versus the use of a
DNS name doubles as an indicator whether or not to reach the CRLDP
via the ACP.
A CRLDP can be reachable across the ACP either by running it on a
node with ACP or by connecting its node via an ACP connect interface
(see Section 8.1).
When using a private PKI for ACP certificates, the CRL may be need-
to-know, for example, to prohibit insight into the operational
practices of the domain by tracking the growth of the CRL. In this
case, HTTPS may be chosen to provide confidentiality, especially when
making the CRL available via the data plane. Authentication and
authorization SHOULD use ACP certificates and the ACP domain
membership check (Section 6.2.3). The CRLDP MAY omit the CRL
verification during authentication of the peer to permit CRL
retrieval by an ACP node with a revoked ACP certificate, which can
allow the (ex) ACP node to quickly discover its ACP certificate
revocation. This may violate the desired need-to-know requirement,
though. ACP nodes MAY support CRLDP operations via HTTPS.
6.2.5.4. Lifetimes
The certificate lifetime may be set to shorter lifetimes than
customary (one year) because certificate renewal is fully automated
via ACP and EST. The primary limiting factor for shorter certificate
lifetimes is the load on the EST server(s) and CA. It is therefore
recommended that ACP certificates are managed via a CA chain where
the assigning CA has enough performance to manage short-lived
certificates. See also Section 9.2.4 for a discussion about an
example setup achieving this. See also "Support for Short-Term,
Automatically Renewed (STAR) Certificates in the Automated
Certificate Management Environment (ACME)" [RFC8739].
When certificate lifetimes are sufficiently short, such as few hours,
certificate revocation may not be necessary, allowing the
simplification of the overall certificate maintenance infrastructure.
See Appendix A.2 for further optimizations of certificate maintenance
when BRSKI can be used [RFC8995].
6.2.5.5. Reenrollment
An ACP node may determine that its ACP certificate has expired, for
example, because the ACP node was powered down or disconnected longer
than its certificate lifetime. In this case, the ACP node SHOULD
convert to a role of a reenrolling candidate ACP node.
In this role, the node maintains the TA and certificate chain
associated with its ACP certificate exclusively for the purpose of
reenrollment, and it attempts (or waits) to get reenrolled with a new
ACP certificate. The details depend on the mechanisms and protocols
used by the ACP registrars.
Please refer to Section 6.11.7 and [RFC8995] for explanations about
ACP registrars and vouchers as used in the following text. When ACP
is intended to be used without BRSKI, the details about BRSKI and
vouchers in the following text can be skipped.
When BRSKI is used (i.e., on ACP nodes that are ANI nodes), the
reenrolling candidate ACP node attempts to enroll like a candidate
ACP node (BRSKI pledge), but instead of using the ACP node's IDevID
certificate, it SHOULD first attempt to use its ACP domain
certificate in the BRSKI TLS authentication. The BRSKI registrar MAY
honor this certificate beyond its expiration date purely for the
purpose of reenrollment. Using the ACP node's domain certificate
allows the BRSKI registrar to learn that node's acp-node-name so that
the BRSKI registrar can reassign the same ACP address information to
the ACP node in the new ACP certificate.
If the BRSKI registrar denies the use of the old ACP certificate, the
reenrolling candidate ACP node MUST reattempt reenrollment using its
IDevID certificate as defined in BRSKI during the TLS connection
setup.
When the BRSKI connection is attempted with either with the old ACP
certificate or the IDevID certificate, the reenrolling candidate ACP
node SHOULD authenticate the BRSKI registrar during TLS connection
setup based on its existing TA certificate chain information
associated with its old ACP certificate. The reenrolling candidate
ACP node SHOULD only fall back to requesting a voucher from the BRSKI
registrar when this authentication fails during TLS connection setup.
As a countermeasure against attacks that attempt to force the ACP
node to forget its prior (expired) certificate and TA, the ACP node
should alternate between attempting to reenroll using its old keying
material and attempting to reenroll with its IDevID and requesting a
voucher.
When mechanisms other than BRSKI are used for ACP certificate
enrollment, the principles of the reenrolling candidate ACP node are
the same. The reenrolling candidate ACP node attempts to
authenticate any ACP registrar peers using reenrollment protocols
and/or mechanisms via its existing certificate chain and/or TA
information and provides its existing ACP certificate and other
identification (such as the IDevID certificate) as necessary to the
registrar.
Maintaining existing TA information is especially important when
using enrollment mechanisms that do not leverage a mechanism to
authenticate the ACP registrar (such as the voucher in BRSKI), and
when the injection of certificate failures could otherwise make the
ACP vulnerable to remote attacks by returning the ACP node to a
"duckling" state in which it accepts enrollment by any network it
connects to. The (expired) ACP certificate and ACP TA SHOULD
therefore be maintained and attempted to be used as one possible
credential for reenrollment until new keying material is acquired.
When using BRSKI or other protocols and/or mechanisms that support
vouchers, maintaining existing TA information allows for lighter-
weight reenrollment of expired ACP certificates, especially in
environments where repeated acquisition of vouchers during the
lifetime of ACP nodes may be operationally expensive or otherwise
undesirable.
6.2.5.6. Failing Certificates
An ACP certificate is called failing in this document if or when the
ACP node to which the certificate was issued can determine that it
was revoked (or explicitly not renewed), or in the absence of such
explicit local diagnostics, when the ACP node fails to connect to
other ACP nodes in the same ACP domain using its ACP certificate. To
determine that the ACP certificate is the culprit of a connection
failure, the peer should pass the domain membership check
(Section 6.2.3), and connection error diagnostics should exclude
other reasons for the connection failure.
This type of failure can happen during the setup or refreshment of a
secure ACP channel connection or during any other use of the ACP
certificate, such as for the TLS connection to an EST server for the
renewal of the ACP domain certificate.
The following are examples of failing certificates that the ACP node
can only discover through connection failure: the domain certificate
or any of its signing certificates could have been revoked or may
have expired, but the ACP node cannot diagnose this condition
directly by itself. Revocation information or clock synchronization
may only be available across the ACP, but the ACP node cannot build
ACP secure channels because the ACP peers reject the ACP node's
domain certificate.
An ACP node SHOULD support the option to determine whether its ACP
certificate is failing, and when it does, put itself into the role of
a reenrolling candidate ACP node as explained in Section 6.2.5.5.
6.3. ACP Adjacency Table
To know to which nodes to establish an ACP channel, every ACP node
maintains an adjacency table. The adjacency table contains
information about adjacent ACP nodes, at a minimum: Node-ID (the
identifier of the node inside the ACP, see Section 6.11.3 and
Section 6.11.5), the interface on which neighbor was discovered (by
GRASP as explained below), the link-local IPv6 address of the
neighbor on that interface, and the certificate (including acp-node-
name). An ACP node MUST maintain this adjacency table. This table
is used to determine to which neighbor an ACP connection is
established.
When the next ACP node is not directly adjacent (i.e., not on a link
connected to this node), the information in the adjacency table can
be supplemented by configuration. For example, the Node-ID and IP
address could be configured. See Section 8.2.
The adjacency table MAY contain information about the validity and
trust of the adjacent ACP node's certificate. However, subsequent
steps MUST always start with the ACP domain membership check against
the peer (see Section 6.2.3).
The adjacency table contains information about adjacent ACP nodes in
general, independent of their domain and trust status. The next step
determines to which of those ACP nodes an ACP connection should be
established.
6.4. Neighbor Discovery with DULL GRASP
Discovery Unsolicited Link-Local (DULL) GRASP is a limited subset of
GRASP intended to operate across an insecure link-local scope. See
Section 2.5.2 of [RFC8990] for its formal definition. The ACP uses
one instance of DULL GRASP for every L2 interface of the ACP node to
discover candidate ACP neighbors that are link-level adjacent.
Unless modified by policy as noted earlier (Section 5, bullet point
2), native interfaces (e.g., physical interfaces on physical nodes)
SHOULD be initialized automatically to a state in which ACP discovery
can be performed, and any native interfaces with ACP neighbors can
then be brought into the ACP even if the interface is otherwise
unconfigured. Reception of packets on such otherwise unconfigured
interfaces MUST be limited so that at first only SLAAC ("IPv6
Stateless Address Autoconfiguration" [RFC4862]) and DULL GRASP work,
and then only the following ACP secure channel setup packets work,
but not any other unnecessary traffic (e.g., no other link-local IPv6
transport stack responders, for example).
Note that the use of the IPv6 link-local multicast address
(ALL_GRASP_NEIGHBORS) implies the need to use MLDv2 (see "Multicast
Listener Discovery Version 2 (MLDv2) for IPv6" [RFC3810]) to announce
the desire to receive packets for that address. Otherwise, DULL
GRASP could fail to operate correctly in the presence of MLD-snooping
switches ("Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping Switches"
[RFC4541]) that either do not support ACP or are not ACP enabled
because those switches would stop forwarding DULL GRASP packets.
Switches that do not support MLD snooping simply need to operate as
pure L2 bridges for IPv6 multicast packets for DULL GRASP to work.
ACP discovery SHOULD NOT be enabled by default on non-native
interfaces. In particular, ACP discovery MUST NOT run inside the ACP
across ACP virtual interfaces. See Section 9.3 for further non-
normative suggestions on how to enable and disable ACP at the node
and interface level. See Section 8.2.2 for more details about
tunnels (typical non-native interfaces). See Section 7 for extending
ACP on devices operating (also) as L2 bridges.
Note: if an ACP node also implements BRSKI to enroll its ACP
certificate (see Appendix A.2 for a summary), then the above
considerations also apply to GRASP discovery for BRSKI. Each DULL
instance of GRASP set up for ACP is then also used for the discovery
of a bootstrap proxy via BRSKI when the node does not have a domain
certificate. Discovery of ACP neighbors happens only when the node
does have the certificate. The node therefore never needs to
discover both a bootstrap proxy and an ACP neighbor at the same time.
An ACP node announces itself to potential ACP peers by use of the
"AN_ACP" objective. This is a synchronization objective intended to
be flooded on a single link using the GRASP Flood Synchronization
(M_FLOOD) message. In accordance with the design of the Flood
Synchronization message, a locator consisting of a specific link-
local IP address, IP protocol number, and port number will be
distributed with the flooded objective. An example of the message is
informally:
[M_FLOOD, 12340815, h'fe80000000000000c0011001feef0000', 210000,
[["AN_ACP", 4, 1, "IKEv2" ],
[O_IPv6_LOCATOR,
h'fe80000000000000c0011001feef0000', IPPROTO_UDP, 15000]]
[["AN_ACP", 4, 1, "DTLS" ],
[O_IPv6_LOCATOR,
h'fe80000000000000c0011001feef0000', IPPROTO_UDP, 17000]]
]
Figure 6: GRASP "AN_ACP" Objective Example
The formal CDDL definition is:
flood-message = [M_FLOOD, session-id, initiator, ttl,
+[objective, (locator-option / [])]]
objective = ["AN_ACP", objective-flags, loop-count,
objective-value]
objective-flags = sync-only ; as in [RFC8990]
sync-only = 4 ; M_FLOOD only requires synchronization
loop-count = 1 ; limit to link-local operation
objective-value = method-name / [ method, *extension ]
method = method-name / [ method-name, *method-param ]
method-name = "IKEv2" / "DTLS" / id
extension = any
method-param = any
id = text .regexp "[A-Za-z@_$]([-.]*[A-Za-z0-9@_$])*"
Figure 7: GRASP "AN_ACP" Definition
The 'objective-flags' field is set to indicate synchronization.
The 'loop-count' is fixed at 1 since this is a link-local operation.
In the above example, the RECOMMENDED period of sending of the
objective is 60 seconds. The indicated 'ttl' of 210000 msec means
that the objective would be cached by ACP nodes even when two out of
three messages are dropped in transit.
The 'session-id' is a random number used for loop prevention
(distinguishing a message from a prior instance of the same message).
In DULL this field is irrelevant but has to be set according to the
GRASP specification.
The originator MUST be the IPv6 link-local address of the originating
ACP node on the sending interface.
The 'method-name' in the 'objective-value' parameter is a string
indicating the protocol available at the specified or implied
locator. It is a protocol supported by the node to negotiate a
secure channel. "IKEv2" as shown in Figure 6 is the protocol used to
negotiate an IPsec secure channel.
The 'method-param' parameter allows method-specific parameters to be
carried. This specification does not define any 'method-param'(s)
for "IKEv2" or "DTLS". Any method-params for these two methods that
are not understood by an ACP node MUST be ignored by it.
The 'extension' parameter allows the definition of method-independent
parameters. This specification does not define any extensions.
Extensions not understood by an ACP node MUST be ignored by it.
The 'locator-option' is optional and is only required when the secure
channel protocol is not offered at a well-defined port number, or if
there is no well-defined port number.
IKEv2 is the actual protocol used to negotiate an IPsec connection.
GRASP therefore indicates "IKEv2" and not "IPsec". If "IPsec" was
used, this could mean the use of the obsolete, older version IKE (v1)
("The Internet Key Exchange (IKE)" [RFC2409]). IKEv2 has an IANA-
assigned port number 500, but in Figure 6, the candidate ACP neighbor
is offering ACP secure channel negotiation via IKEv2 on port 15000
(purely to show through the example that GRASP allows the indication
of a port number, and it does not have to be IANA assigned).
There is no default UDP port for DTLS, it is always locally assigned
by the node. For further details about the "DTLS" secure channel
protocol, see Section 6.8.4.
If a locator is included, it MUST be an O_IPv6_LOCATOR, and the IPv6
address MUST be the same as the initiator address (these are DULL
requirements to minimize third-party DoS attacks).
The secure channel methods defined in this document use "IKEv2" and
"DTLS" for 'objective-value'. There is no distinction between IKEv2
native and GRE-IKEv2 because this is purely negotiated via IKEv2.
A node that supports more than one secure channel protocol method
needs to flood multiple versions of the "AN_ACP" objective so that
each method can be accompanied by its own 'locator-option'. This can
use a single GRASP M_FLOOD message as shown in Figure 6.
The primary use of DULL GRASP is to discover the link-local IPv6
address of candidate ACP peers on subnets. The signaling of the
supported secure channel option is primarily for diagnostic purposes,
but it is also necessary for discovery when the protocol has no well-
known transport address, such as in the case of DTLS.
Note that a node serving both as an ACP node and BRSKI Join Proxy may
choose to distribute the "AN_ACP" objective and the respective BRSKI
in the same M_FLOOD message, since GRASP allows multiple objectives
in one message. This may be impractical, though, if ACP and BRSKI
operations are implemented via separate software modules and/or ASAs.
The result of the discovery is the IPv6 link-local address of the
neighbor as well as its supported secure channel protocols (and the
non-standard port they are running on). It is stored in the ACP
adjacency table (see Section 6.3), which then drives the further
building of the ACP to that neighbor.
Note that the described DULL GRASP objective intentionally does not
include the ACP node's ACP certificate, even though this would be
useful for diagnostics and to simplify the security exchange in ACP
secure channel security association protocols (see Section 6.8). The
reason is that DULL GRASP messages are periodically multicast across
IPv6 subnets, and full certificates could easily lead to fragmented
IPv6 DULL GRASP multicast packets due to the size of a certificate.
This would be highly undesirable.
6.5. Candidate ACP Neighbor Selection
An ACP node determines to which other ACP nodes in the adjacency
table it should attempt to build an ACP connection. This is based on
the information in the ACP adjacency table.
The ACP is established exclusively between nodes in the same domain.
This includes all routing subdomains. Appendix A.6 explains how ACP
connections across multiple routing subdomains are special.
The result of the candidate ACP neighbor selection process is a list
of adjacent or configured autonomic neighbors to which an ACP channel
should be established. The next step begins that channel
establishment.
6.6. Channel Selection
To avoid attacks, the initial discovery of candidate ACP peers cannot
include any unprotected negotiation. To avoid reinventing and
validating security association mechanisms, the next step after
discovering the address of a candidate neighbor is to establish a
security association with that neighbor using a well-known security
association method.
It seems clear from the use cases that not all types of ACP nodes can
or need to connect directly to each other, nor are they able to
support or prefer all possible mechanisms. For example, IoT devices
that are codespace limited may only support DTLS because that code
exists already on them for end-to-end security, but low-end, in-
ceiling L2 switches may only want to support Media Access Control
Security (MacSec, see 802.1AE [MACSEC]) because that is also
supported in their chips. Only a flexible gateway device may need to
support both of these mechanisms and potentially more. Note that
MacSec is not required by any profiles of the ACP in this
specification. Instead, MacSec is mentioned as an interesting
potential secure channel protocol. Note also that the security model
allows and requires any-to-any authentication and authorization
between all ACP nodes because there is not only hop-by-hop but also
end-to-end authentication for secure channels.
To support extensible selection of the secure channel protocol
without a single common mandatory-to-implement (MTI) protocol, an ACP
node MUST try all the ACP secure channel protocols it supports and
that are also announced by the candidate ACP neighbor via its
"AN_ACP" GRASP parameters (these are called the "feasible" ACP secure
channel protocols).
To ensure that the selection of the secure channel protocols always
succeeds in a predictable fashion without blocking, the following
rules apply:
* An ACP node may choose to attempt to initiate the different
feasible ACP secure channel protocols it supports according to its
local policies sequentially or in parallel, but it MUST support
acting as a responder to all of them in parallel.
* Once the first ACP secure channel protocol connection to a
specific peer IPv6 address passes peer authentication, the two
peers know each other's certificate because those ACP certificates
are used by all secure channel protocols for mutual
authentication. The peer with the higher Node-ID in the
AcpNodeName of its ACP certificate takes on the role of the
Decider towards the peer. The other peer takes on the role of the
Follower. The Decider selects which secure channel protocol to
ultimately use.
* The Follower becomes passive: it does not attempt to further
initiate ACP secure channel protocol connections with the Decider
and does not consider it to be an error when the Decider closes
secure channels. The Decider becomes the active party, continuing
to attempt the setup of secure channel protocols with the
Follower. This process terminates when the Decider arrives at the
"best" ACP secure channel connection option that also works with
the Follower ("best" from the Decider's point of view).
* A peer with a "0" acp-address in its AcpNodeName takes on the role
of Follower when peering with a node that has a non-"0" acp-
address (note that this specification does not fully define the
behavior of ACP secure channel negotiation for nodes with a "0"
ACP address field, it only defines interoperability with such ACP
nodes).
In a simple example, ACP peer Node 1 attempts to initiate an IPsec
connection via IKEv2 to peer Node 2. The IKEv2 authentication
succeeds. Node 1 has the lower ACP address and becomes the Follower.
Node 2 becomes the Decider. IKEv2 might not be the preferred ACP
secure channel protocol for the Decider Node 2. Node 2 would
therefore proceed to attempt secure channel setups with more
preferred protocol options (in its view, e.g., DTLS/UDP). If any
such preferred ACP secure channel connection of the Decider succeeds,
it would close the IPsec connection. If Node 2 has no preferred
protocol option over IPsec, or no such connection attempt from Node 2
to Node 1 succeeds, Node 2 would keep the IPsec connection and use
it.
The Decider SHOULD NOT send actual payload packets across a secure
channel until it has decided to use it. The Follower MAY delay
linking the ACP secure channel to the ACP virtual interface until it
sees the first payload packet from the Decider up to a maximum of 5
seconds to avoid unnecessarily linking a secure channel that will be
terminated as undesired by the Decider shortly afterward.
The following sequence of steps show this example in more detail.
Each step is tagged with [<step#>{:<connection>}]. The connection is
included to more easily distinguish which of the two competing
connections the step belongs to, one initiated by Node 1, one
initiated by Node 2.
[1] Node 1 sends GRASP "AN_ACP" message to announce itself.
[2] Node 2 sends GRASP "AN_ACP" message to announce itself.
[3] Node 2 receives [1] from Node 1.
[4:C1] Because of [3], Node 2 starts as initiator on its preferred
secure channel protocol towards Node 1. Connection C1.
[5] Node 1 receives [2] from Node 2.
[6:C2] Because of [5], Node 1 starts as initiator on its preferred
secure channel protocol towards Node 2. Connection C2.
[7:C1] Node 1 and Node 2 have authenticated each other's
certificate on connection C1 as valid ACP peers.
[8:C1] Node 1's certificate has a lower ACP Node-ID than Node 2's,
therefore Node 1 considers itself the Follower and Node 2
the Decider on connection C1. Connection setup C1 is
completed.
[9] Node 1 refrains from attempting any further secure channel
connections to Node 2 (the Decider) as learned from [2]
because it knows from [8:C1] that it is the Follower
relative to Node 2.
[10:C2] Node 1 and Node 2 have authenticated each other's
certificate on connection C2 (like [7:C1]).
[11:C2] Node 1's certificate has a lower ACP Node-ID than Node 2's,
therefore Node 1 considers itself the Follower and Node 2
the Decider on connection C2, but they also identify that
C2 is to the same mutual peer as their C1, so this has no
further impact: the roles Decider and Follower where
already assigned between these two peers by [8:C1].
[12:C2] Node 2 (the Decider) closes C1. Node 1 is fine with this,
because of its role as the Follower (from [8:C1]).
[13] Node 2 (the Decider) and Node 1 (the Follower) start data
transfer across C2, which makes it become a secure channel
for the ACP.
All this negotiation is in the context of an L2 interface. The
Decider and Follower will build ACP connections to each other on
every L2 interface that they both connect to. An autonomic node MUST
NOT assume that neighbors with the same L2 or link-local IPv6
addresses on different L2 interfaces are the same node. This can
only be determined after examining the certificate after a successful
security association attempt.
The Decider SHOULD NOT suppress attempting a particular ACP secure
channel protocol connection on one L2 interface because this type of
ACP secure channel connection has failed to the peer with the same
ACP certificate on another L2 interface: not only may the supported
ACP secure channel protocol options be different on the same ACP peer
across different L2 interfaces, but also error conditions may cause
inconsistent failures across different L2 interfaces. Avoiding such
connection attempt optimizations can therefore help to increase
robustness in the case of errors.
6.7. Candidate ACP Neighbor Verification
Independent of the security association protocol chosen, candidate
ACP neighbors need to be authenticated based on their domain
certificate. This implies that any secure channel protocol MUST
support certificate-based authentication that can support the ACP
domain membership check as defined in Section 6.2.3. If it fails,
the connection attempt is aborted and an error logged. Attempts to
reconnect MUST be throttled. The RECOMMENDED default is exponential
base-two backoff with an initial retransmission time (IRT) of 10
seconds and a maximum retransmission time (MRT) of 640 seconds.
Failure to authenticate an ACP neighbor when acting in the role of a
responder of the security authentication protocol MUST NOT impact the
attempts of the ACP node to attempt establishing a connection as an
initiator. Only failed connection attempts as an initiator must
cause throttling. This rule is meant to increase resilience of
secure channel creation. Section 6.6 shows how simultaneous mutual
secure channel setup collisions are resolved.
6.8. Security Association (Secure Channel) Protocols
This section describes how ACP nodes establish secured data
connections to automatically discovered or configured peers in the
ACP. Section 6.4 describes how peers that are adjacent on an IPv6
subnet are discovered automatically. Section 8.2 describes how to
configure peers that are not adjacent on an IPv6 subnet.
Section 6.13.5.2 describes how secure channels are mapped to virtual
IPv6 subnet interfaces in the ACP. The simple case is to map every
ACP secure channel to a separate ACP point-to-point virtual interface
(Section 6.13.5.2.1). When a single subnet has multiple ACP peers,
this results in multiple ACP point-to-point virtual interfaces across
that underlying multiparty IPv6 subnet. This can be optimized with
ACP multi-access virtual interfaces (Section 6.13.5.2.2), but the
benefits of that optimization may not justify the complexity of that
option.
6.8.1. General Considerations
Due to channel selection (Section 6.6), ACP can support an evolving
set of security association protocols and does not require support
for a single network-wide MTI. ACP nodes only need to implement
those protocols required to interoperate with their candidate peers,
not with potentially any node in the ACP domain. See Section 6.8.5
for an example of this.
The degree of security required on every hop of an ACP network needs
to be consistent across the network so that there is no designated
"weakest link" because it is that "weakest link" that would otherwise
become the designated point of attack. When the secure channel
protection on one link is compromised, it can be used to send and/or
receive packets across the whole ACP network. Therefore, even though
the security association protocols can be different, their minimum
degree of security should be comparable.
Secure channel protocols do not need to always support arbitrary
Layer 3 (L3) connectivity between peers, but can leverage the fact
that the standard use case for ACP secure channels is an L2
adjacency. Hence, L2 dependent mechanisms could be adopted for use
as secure channel association protocols.
L2 mechanisms such as strong encrypted radio technologies or [MACSEC]
may offer equivalent encryption, and the ACP security association
protocol may only be required to authenticate ACP domain membership
of a peer and/or derive a key for the L2 mechanism. Mechanisms that
leverage such underlying L2 security to auto-discover and associate
ACP peers are possible and desirable to avoid duplication of
encryption, but none are specified in this document.
Strong physical security of a link may stand in where cryptographic
security is infeasible. As there is no secure mechanism to
automatically discover strong physical security solely between two
peers, it can only be used with explicit configuration, and that
configuration too could become an attack vector. This document
therefore specifies with ACP connect (Section 8.1) only one
explicitly configured mechanism without any secure channel
association protocol for the case where both the link and the nodes
attached to it have strong physical security.
6.8.2. Common Requirements
The authentication of peers in any security association protocol MUST
use the ACP certificate according to Section 6.2.3. Because auto-
discovery of candidate ACP neighbors via GRASP (see Section 6.4) as
specified in this document does not communicate the neighbor's ACP
certificate, and ACP nodes may not (yet) have any other network
connectivity to retrieve certificates, any security association
protocol MUST use a mechanism to communicate the certificate directly
instead of relying on a referential mechanism such as communicating
only a hash and/or URL for the certificate.
A security association protocol MUST use Forward Secrecy (whether
inherently or as part of a profile of the security association
protocol).
Because the ACP payload of legacy protocol payloads inside the ACP
and hop-by-hop ACP flooded GRASP information is unencrypted, the ACP
secure channel protocol requires confidentiality. Symmetric
encryption for the transmission of secure channel data MUST use
encryption schemes considered to be security wise equal to or better
than 256-bit key strength, such as AES-256. There MUST NOT be
support for NULL encryption.
Security association protocols typically only signal the end entity
certificate (e.g., the ACP certificate) and any possible intermediate
CA certificates for successful mutual authentication. The TA has to
be mutually known and trusted, and therefore its certificate does not
need to be signaled for successful mutual authentication.
Nevertheless, for use with ACP secure channel setup, there SHOULD be
the option to include the TA certificate in the signaling to aid
troubleshooting, see Section 9.1.1.
Signaling of TA certificates may not be appropriate when the
deployment relies on a security model where the TA certificate
content is considered confidential, and only its hash is appropriate
for signaling. ACP nodes SHOULD have a mechanism to select whether
the TA certificate is signaled or not, assuming that both options are
possible with a specific secure channel protocol.
An ACP secure channel MUST immediately be terminated when the
lifetime of any certificate in the chain used to authenticate the
neighbor expires or becomes revoked. This may not be standard
behavior in secure channel protocols because the certificate
authentication may only influence the setup of the secure channel in
these protocols, but may not be revalidated during the lifetime of
the secure connection in the absence of this requirement.
When specifying an additional security association protocol for ACP
secure channels beyond those covered in this document, any protocol
options that are unnecessary for the support of devices that are
expected to be able to support the ACP SHOULD be eliminated in order
to minimize implementation complexity. For example, definitions for
security protocols often include old and/or inferior security options
required only to interoperate with existing devices that cannot
update to the currently preferred security options. Such old and/or
inferior security options do not need to be supported when a security
association protocol is first specified for the ACP, thus
strengthening the "weakest link" and simplifying ACP implementation
overhead.
6.8.3. ACP via IPsec
An ACP node announces its ability to support IPsec, negotiated via
IKEv2, as the ACP secure channel protocol using the "IKEv2"
'objective-value' in the "AN_ACP" GRASP objective.
The ACP usage of IPsec and IKEv2 mandates a profile with a narrow set
of options of the current Standards Track usage guidance for IPsec
("Cryptographic Algorithm Implementation Requirements and Usage
Guidance for Encapsulating Security Payload (ESP) and Authentication
Header (AH)" [RFC8221]) and IKEv2 ("Algorithm Implementation
Requirements and Usage Guidance for the Internet Key Exchange
Protocol Version 2 (IKEv2)" [RFC8247]). These options result in
stringent security properties and can exclude deprecated and legacy
algorithms because there is no need for interoperability with legacy
equipment for ACP secure channels. Any such backward compatibility
would lead only to an increased attack surface and implementation
complexity, for no benefit.
6.8.3.1. Native IPsec
An ACP node that is supporting native IPsec MUST use IPsec in tunnel
mode, negotiated via IKEv2, and with IPv6 payload (e.g., ESP Next
Header of 41). It MUST use local and peer link-local IPv6 addresses
for encapsulation. Manual keying MUST NOT be used, see Section 6.2.
Traffic Selectors are:
TSi = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
IPsec tunnel mode is required because the ACP will route and/or
forward packets received from any other ACP node across the ACP
secure channels, and not only its own generated ACP packets. With
IPsec transport mode (and no additional encapsulation header in the
ESP payload), it would only be possible to send packets originated by
the ACP node itself because the IPv6 addresses of the ESP must be the
same as that of the outer IPv6 header.
6.8.3.1.1. RFC 8221 (IPsec/ESP)
ACP IPsec implementations MUST comply with [RFC8221] and any
specifications that update it. The requirements from above and this
section amend and supersede its requirements.
The IP Authentication Header (AH) MUST NOT be used (because it does
not provide confidentiality).
For the required ESP encryption algorithms in Section 5 of [RFC8221],
the following guidance applies:
* ENCR_NULL AH MUST NOT be used (because it does not provide
confidentiality).
* ENCR_AES_GCM_16 is the only MTI ESP encryption algorithm for ACP
via IPsec/ESP (it is already listed as MUST in [RFC8221]).
* ENCR_AES_CBC with AUTH_HMAC_SHA2_256_128 (as the ESP
authentication algorithm) and ENCR_AES_CCM_8 MAY be supported. If
either provides higher performance than ENCR_AES_GCM_16, it SHOULD
be supported.
* ENCR_CHACHA20_POLY1305 SHOULD be supported at equal or higher
performance than ENCR_AES_GCM_16. If that performance is not
feasible, it MAY be supported.
IKEv2 indicates an order for the offered algorithms. The algorithms
SHOULD be ordered by performance. The first algorithm supported by
both sides is generally chosen.
Explanations:
* There is no requirement to interoperate with legacy equipment in
ACP secure channels, so a single MTI encryption algorithm for
IPsec in ACP secure channels is sufficient for interoperability
and allows for the most lightweight implementations.
* ENCR_AES_GCM_16 is an Authenticated Encryption with Associated
Data (AEAD) cipher mode, so no additional ESP authentication
algorithm is needed, simplifying the MTI requirements of IPsec for
the ACP.
* There is no MTI requirement for the support of ENCR_AES_CBC
because ENCR_AES_GCM_16 is assumed to be feasible with less cost
and/or higher performance in modern devices' hardware-accelerated
implementations compared to ENCR-AES_CBC.
* ENCR_CHACHA20_POLY1305 is mandatory in [RFC8221] because of its
target use as a fallback algorithm in case weaknesses in AES are
uncovered. Unfortunately, there is currently no way to
automatically propagate across an ACP a policy to disallow use of
AES-based algorithms, so this target benefit of
ENCR_CHACHA20_POLY1305 cannot fully be adopted yet for the ACP.
Therefore, this algorithm is only recommended. Changing from AES
to this algorithm with a potentially big drop in performance could
also render the ACP inoperable. Therefore, there is a performance
requirement against this algorithm so that it could become an
effective security backup to AES for the ACP once a policy to
switch over to it or prefer it is available in an ACP framework.
[RFC8221] allows for 128-bit or 256-bit AES keys. This document
mandates that only 256-bit AES keys MUST be supported.
When [RFC8221] is updated, ACP implementations will need to consider
legacy interoperability.
6.8.3.1.2. RFC 8247 (IKEv2)
[RFC8247] provides a baseline recommendation for mandatory-to-
implement ciphers, integrity checks, pseudorandom functions, and
Diffie-Hellman mechanisms. Those recommendations, and the
recommendations of subsequent documents, apply as well to the ACP.
Because IKEv2 for ACP secure channels is sufficient to be implemented
in control plane software rather than in Application-Specific
Integrated Circuit (ASIC) hardware, and ACP nodes supporting IKEv2
are not assumed to be code space constrained, and because existing
IKEv2 implementations are expected to support [RFC8247]
recommendations, this document makes no attempt to simplify its
recommendations for use with the ACP.
See [IKEV2IANA] for IANA IKEv2 parameter names used in this text.
ACP nodes supporting IKEv2 MUST comply with [RFC8247] amended by the
following requirements, which constitute a policy statement as
permitted by [RFC8247].
To signal the ACP certificate chain (including TA) as required by
Section 6.8.2, the "X.509 Certificate - Signature" payload in IKEv2
can be used. It is mandatory according to [RFC7296], Section 3.6.
ACP nodes SHOULD set up IKEv2 to only use the ACP certificate and TA
when acting as an IKEv2 responder on the IPv6 link-local address and
port number indicated in the "AN_ACP" DULL GRASP announcements (see
Section 6.4).
When CERTREQ is received from a peer, and it does not indicate any of
this ACP node's TA certificates, the ACP node SHOULD ignore the
CERTREQ and continue sending its certificate chain including its TA
as subject to the requirements and explanations in Section 6.8.2.
This will not result in successful mutual authentication but assists
diagnostics.
Note that with IKEv2, failing authentication will only result in the
responder receiving the certificate chain from the initiator, but not
vice versa. Because ACP secure channel setup is symmetric (see
Section 6.7), every non-malicious ACP neighbor will attempt to
connect as an initiator, though, allowing it to obtain the diagnostic
information about the neighbor's certificate.
In IKEv2, ACP nodes are identified by their ACP addresses. The
ID_IPv6_ADDR IKEv2 identification payload MUST be used and MUST
convey the ACP address. If the peer's ACP certificate includes a
32HEXDIG ACP address in the acp-node-name (not "0" or omitted), the
address in the IKEv2 identification payload MUST match it. See
Section 6.2.3 for more information about "0" or omitted ACP address
fields in the acp-node-name.
IKEv2 authentication MUST use authentication method 14 ("Digital
Signature") for ACP certificates; this authentication method can be
used with both RSA and ECDSA certificates, indicated by an ASN.1
object AlgorithmIdentifier.
The Digital Signature hash SHA2-512 MUST be supported (in addition to
SHA2-256).
The IKEv2 Diffie-Hellman key exchange group 19 (256-bit random ECP),
MUST be supported. Reason: ECC provides a similar security level to
finite-field (modular exponentiation (MODP)) key exchange with a
shorter key length, so is generally preferred absent other
considerations.
6.8.3.2. IPsec with GRE Encapsulation
In network devices, it is often more common to implement high-
performance virtual interfaces on top of GRE encapsulation than on
top of a "native" IPsec association (without any other encapsulation
than those defined by IPsec). On those devices, it may be beneficial
to run the ACP secure channel on top of GRE protected by the IPsec
association.
The requirements for ESP/IPsec/IKEv2 with GRE are the same as for
native IPsec (see Section 6.8.3.1) except that IPsec transport mode
and next protocol GRE (47) are to be negotiated. Tunnel mode is not
required because of GRE. Traffic Selectors are:
TSi = (47, 0-65535, Initiator-IPv6-LL-addr ... Initiator-IPv6-LL-addr)
TSr = (47, 0-65535, Responder-IPv6-LL-addr ... Responder-IPv6-LL-addr)
If the IKEv2 initiator and responder support IPsec over GRE, it will
be preferred over native IPsec because of how IKEv2 negotiates
transport mode (as used by this IPsec over GRE profile) versus tunnel
mode as used by native IPsec (see Section 1.3.1 of [RFC7296]). The
ACP IPv6 traffic has to be carried across GRE according to "IPv6
Support for Generic Routing Encapsulation (GRE)" [RFC7676].
6.8.4. ACP via DTLS
This document defines the use of ACP via DTLS on the assumption that
it is likely the first transport encryption supported in some classes
of constrained devices: DTLS is commonly used in constrained devices
when IPsec is not. Code space on those devices may be also be too
limited to support more than the minimum number of required
protocols.
An ACP node announces its ability to support DTLS version 1.2
("Datagram Transport Layer Security Version 1.2" [RFC6347]) compliant
with the requirements defined in this document as an ACP secure
channel protocol in GRASP through the "DTLS" 'objective-value' in the
"AN_ACP" objective (see Section 6.4).
To run ACP via UDP and DTLS, a locally assigned UDP port is used that
is announced as a parameter in the GRASP "AN_ACP" objective to
candidate neighbors. This port can also be any newer version of DTLS
as long as that version can negotiate a DTLS 1.2 connection in the
presence of a peer that only supports DTLS 1.2.
All ACP nodes supporting DTLS as a secure channel protocol MUST
adhere to the DTLS implementation recommendations and security
considerations of BCP 195 [RFC7525] except with respect to the DTLS
version. ACP nodes supporting DTLS MUST support DTLS 1.2. They MUST
NOT support older versions of DTLS.
Unlike for IPsec, no attempts are made to simplify the requirements
of the recommendations in BCP 195 [RFC7525] because the expectation
is that DTLS would use software-only implementations where the
ability to reuse widely adopted implementations is more important
than the ability to minimize the complexity of a hardware-accelerated
implementation, which is known to be important for IPsec.
DTLS 1.3 [TLS-DTLS13] is "backward compatible" with DTLS 1.2 (see
Section 1 of [TLS-DTLS13]). A DTLS implementation supporting both
DTLS 1.2 and DTLS 1.3 does comply with the above requirements of
negotiating to DTLS 1.2 in the presence of a DTLS 1.2 only peer, but
using DTLS 1.3 when booth peers support it.
Version 1.2 is the MTI version of DTLS in this specification because
of the following:
* There is more experience with DTLS 1.2 across the spectrum of
target ACP nodes.
* Firmware of lower-end, embedded ACP nodes may not support a newer
version for a long time.
* There are significant changes with DTLS 1.3, such as a different
record layer requiring time to gain implementation and deployment
experience especially on lower-end devices with limited code
space.
* The existing BCP [RFC7525] for DTLS 1.2 may take an equally longer
time to be updated with experience from a newer DTLS version.
* There are no significant benefits of DTLS 1.3 over DTLS 1.2 that
are use-case relevant in the context of the ACP options for DTLS.
For example, signaling performance improvements for session setup
in DTLS 1.3 is not important for the ACP given the long-lived
nature of ACP secure channel connections and the fact that DTLS
connections are mostly link local (short RTT).
Nevertheless, newer versions of DTLS, such as DTLS 1.3, have stricter
security requirements, and the use of the latest standard protocol
version is in general recommended for IETF security standards.
Therefore, ACP implementations are advised to support all the newer
versions of DTLS that can still negotiate down to DTLS 1.2.
There is no additional session setup or other security association
besides this simple DTLS setup. As soon as the DTLS session is
functional, the ACP peers will exchange ACP IPv6 packets as the
payload of the DTLS transport connection. Any DTLS-defined security
association mechanisms such as rekeying are used as they would be for
any transport application relying solely on DTLS.
6.8.5. ACP Secure Channel Profiles
As explained in the beginning of Section 6.6, there is no single
secure channel mechanism mandated for all ACP nodes. Instead, this
section defines two ACP profiles, "baseline" and "constrained", for
ACP nodes that do introduce such requirements.
An ACP node supporting the baseline profile MUST support IPsec
natively and MAY support IPsec via GRE. An ACP node supporting the
constrained profile that cannot support IPsec MUST support DTLS. An
ACP node connecting an area of constrained ACP nodes with an area of
baseline ACP nodes needs to support both IPsec and DTLS and therefore
supports both the baseline and constrained profiles.
Explanation: not all types of ACP nodes are able to or need to
connect directly to each other, nor are they able to support or
prefer all possible secure channel mechanisms. For example, IoT
devices with limited code space may only support DTLS because that
code already exists on them for end-to-end security, but high-end
core routers may not want to support DTLS because they can perform
IPsec in accelerated hardware, but they would need to support DTLS in
an underpowered CPU forwarding path shared with critical control
plane operations. This is not a deployment issue for a single ACP
across these types of nodes as long as there are also appropriate
gateway ACP nodes that sufficiently support many secure channel
mechanisms to allow interconnecting areas of ACP nodes with a more
constrained set of secure channel protocols. On the edge between IoT
areas and high-end core networks, general-purpose routers that act as
those gateways and that can support a variety of secure channel
protocols are the norm already.
Native IPsec with tunnel mode provides the shortest encapsulation
overhead. GRE may be preferred by legacy implementations because, in
the past, the virtual interfaces required by ACP design in
conjunction with secure channels have been implemented more often for
GRE than purely for native IPsec.
ACP nodes need to specify the set of secure ACP mechanisms they
support in documentation and should declare which profile they
support according to the above requirements.
6.9. GRASP in the ACP
6.9.1. GRASP as a Core Service of the ACP
The ACP MUST run an instance of GRASP inside of it. It is a key part
of the ACP services. The function in GRASP that makes it fundamental
as a service of the ACP is the ability to provide ACP-wide service
discovery (using objectives in GRASP).
ACP provides IP unicast routing via RPL (see Section 6.12).
The ACP does not use IP multicast routing nor does it provide generic
IP multicast services (the handling of GRASP link-local multicast
messages is explained in Section 6.9.2). Instead, the ACP provides
service discovery via the objective discovery/announcement and
negotiation mechanisms of the ACP GRASP instance (services are a form
of objectives). These mechanisms use hop-by-hop reliable flooding of
GRASP messages for both service discovery (GRASP M_DISCOVERY
messages) and service announcement (GRASP M_FLOOD messages).
See Appendix A.5 for discussion about this design choice of the ACP.
6.9.2. ACP as the Security and Transport Substrate for GRASP
In the terminology of GRASP [RFC8990], the ACP is the security and
transport substrate for the GRASP instance run inside the ACP ("ACP
GRASP").
This means that the ACP is responsible for ensuring that this
instance of GRASP is only sending messages across the ACP GRASP
virtual interfaces. Whenever the ACP adds or deletes such an
interface because of new ACP secure channels or loss thereof, the ACP
needs to indicate this to the ACP instance of GRASP. The ACP exists
also in the absence of any active ACP neighbors. It is created when
the node has a domain certificate, and it continues to exist even if
all of its neighbors cease operation.
In this case, ASAs using GRASP running on the same node still need to
be able to discover each other's objectives. When the ACP does not
exist, ASAs leveraging the ACP instance of GRASP via APIs MUST still
be able to operate, and they MUST be able to understand that there is
no ACP and that therefore the ACP instance of GRASP cannot operate.
How the ACP acts as the security and transport substrate for GRASP is
shown in Figure 8.
GRASP unicast messages inside the ACP always use the ACP address.
Link-local addresses from the ACP VRF MUST NOT be used inside
objectives. GRASP unicast messages inside the ACP are transported
via TLS. See Section 6.1 for TLS requirements. TLS mutual
authentication MUST use the ACP domain membership check defined in
Section 6.2.3.
GRASP link-local multicast messages are targeted for a specific ACP
virtual interface (as defined Section 6.13.5), but they are sent by
the ACP to an ACP GRASP virtual interface that is constructed from
the TCP connection(s) to the IPv6 link-local neighbor address(es) on
the underlying ACP virtual interface. If the ACP GRASP virtual
interface has two or more neighbors, the GRASP link-local multicast
messages are replicated to all neighbor TCP connections.
TCP and TLS connections for GRASP in the ACP use the IANA-assigned
TCP port for GRASP (7017). Effectively, the transport stack is
expected to be TLS for connections to and from the ACP address (e.g.,
global-scope address(es)) and TCP for connections to and from the
link-local addresses on the ACP virtual interfaces. The latter ones
are only used for the flooding of GRASP messages.
..............................ACP..............................
. .
. /-GRASP-flooding-\ ACP GRASP instance .
. / \ A
. GRASP GRASP GRASP C
. link-local unicast link-local P
. multicast messages multicast .
. messages | messages .
. | | | .
...............................................................
. v v v ACP security and transport .
. | | | substrate for GRASP .
. | | | .
. | ACP GRASP | - ACP GRASP A
. | loopback | loopback interface C
. | interface | - ACP-cert auth P
. | TLS | .
. ACP GRASP | ACP GRASP - ACP GRASP virtual .
. subnet1 | subnet2 interfaces .
. TCP | TCP .
. | | | .
...............................................................
. | | | ^^^ Users of ACP (GRASP/ASA) .
. | | | ACP interfaces/addressing .
. | | | .
. | | | A
. | ACP loopback interf.| <- ACP loopback interface C
. | ACP-address | - address (global ULA) P
. subnet1 | subnet2 <- ACP virtual interfaces .
. link-local | link-local - link-local addresses .
...............................................................
. | | | ACP VRF .
. | RPL-routing | virtual routing and forwarding .
. | /IP-Forwarding\ | A
. | / \ | C
. ACP IPv6 packets ACP IPv6 packets P
. |/ \| .
. IPsec/DTLS IPsec/DTLS - ACP-cert auth .
...............................................................
| | Data Plane
| |
| | - ACP secure channel
link-local link-local - encapsulation addresses
subnet1 subnet2 - data plane interfaces
| |
ACP-Nbr1 ACP-Nbr2
Figure 8: ACP as Security and Transport Substrate for GRASP
6.9.2.1. Discussion
TCP encapsulation for GRASP M_DISCOVERY and M_FLOOD link-local
messages is used because these messages are flooded across
potentially many hops to all ACP nodes, and a single link with even
temporary packet-loss issues (e.g., a Wi-Fi or Powerline link) can
reduce the probability for loss-free transmission so much that
applications would want to increase the frequency with which they
send these messages. Such shorter periodic retransmission of
datagrams would result in more traffic and processing overhead in the
ACP than the hop-by-hop, reliable retransmission mechanism offered by
TCP and duplicate elimination by GRASP.
TLS is mandated for GRASP non-link-local unicast because the ACP
secure channel mandatory authentication and encryption protects only
against attacks from the outside but not against attacks from the
inside: compromised ACP members that have (not yet) been detected and
removed (e.g., via domain certificate revocation and/or expiry).
If GRASP peer connections were to use just TCP, compromised ACP
members could simply eavesdrop passively on GRASP peer connections
for which they are on-path ("man in the middle" or MITM) or intercept
and modify messages. With TLS, it is not possible to completely
eliminate problems with compromised ACP members, but attacks are a
lot more complex.
Eavesdropping and/or spoofing by a compromised ACP node is still
possible because in the model of the ACP and GRASP, the provider and
consumer of an objective have initially no unique information (such
as an identity) about the other side that would allow them to
distinguish a benevolent from a compromised peer. The compromised
ACP node would simply announce the objective as well, potentially
filter the original objective in GRASP when it is a MITM and act as
an application-level proxy. This of course requires that the
compromised ACP node understand the semantics of the GRASP
negotiation to an extent that allows the compromised node to proxy
the messages without being detected, but in an ACP environment, this
is quite likely public knowledge or even standardized.
The GRASP TLS connections are run the same as any other ACP traffic
through the ACP secure channels. This leads to double authentication
and encryption, which has the following benefits:
* Secure channel methods such as IPsec may provide protection
against additional attacks, for example, reset attacks.
* The secure channel method may leverage hardware acceleration, and
there may be little or no gain in eliminating it.
* The security model for ACP GRASP is no different than other ACP
traffic. Instead, there is just another layer of protection
against certain attacks from the inside, which is important due to
the role of GRASP in the ACP.
6.10. Context Separation
The ACP is in a separate context from the normal data plane of the
node. This context includes the ACP channels' IPv6 forwarding and
routing as well as any required higher-layer ACP functions.
In a classical network system, a dedicated VRF is one logical
implementation option for the ACP. If allowed by the system's
software architecture, separation options that minimize shared
components, such as a logical container or virtual machine instance,
are preferred. The context for the ACP needs to be established
automatically during the bootstrap of a node. As much as possible,
it should be protected from being modified unintentionally by (data
plane) configuration.
Context separation improves security because the ACP is not reachable
from the data plane routing or forwarding table(s). Also,
configuration errors from the data plane setup do not affect the ACP.
6.11. Addressing inside the ACP
The channels explained above typically only establish communication
between two adjacent nodes. In order for communication to happen
across multiple hops, the Autonomic Control Plane requires ACP
network-wide valid addresses and routing. Each ACP node creates a
loopback interface with an ACP network-wide unique address (prefix)
inside the ACP context (as explained in Section 6.10). This address
may be used also in other virtual contexts.
With the algorithm introduced here, all ACP nodes in the same routing
subdomain have the same /48 ULA prefix. Conversely, ULA Global IDs
from different domains are unlikely to clash, such that two ACP
networks can be merged, as long as the policy allows that merge. See
also Section 10.1 for a discussion on merging domains.
Links inside the ACP only use link-local IPv6 addressing, such that
each node's ACP only requires one routable address prefix.
6.11.1. Fundamental Concepts of Autonomic Addressing
* Usage: autonomic addresses are exclusively used for self-
management functions inside a trusted domain. They are not used
for user traffic. Communications with entities outside the
trusted domain use another address space, for example, a normally
managed routable address space (called "data plane" in this
document).
* Separation: autonomic address space is used separately from user
address space and other address realms. This supports the
robustness requirement.
* Loopback only: only ACP loopback interfaces (and potentially those
configured for ACP connect, see Section 8.1) carry routable
address(es); all other interfaces (called ACP virtual interfaces)
only use IPv6 link-local addresses. The usage of IPv6 link-local
addressing is discussed in "Using Only Link-Local Addressing
inside an IPv6 Network" [RFC7404].
* Use of ULA: for loopback interfaces of ACP nodes, we use ULA with
the L bit set to 1 (as defined in Section 3.1 of [RFC4193]). Note
that the random hash for ACP loopback addresses uses the
definition in Section 6.11.2 and not the one in [RFC4193],
Section 3.2.2.
* No external connectivity: the addresses do not provide access to
the Internet. If a node requires further connectivity, it should
use another, traditionally managed addressing scheme in parallel.
* Addresses in the ACP are permanent and do not support temporary
addresses as defined in "Temporary Address Extensions for
Stateless Address Autoconfiguration in IPv6" [RFC8981].
* Addresses in the ACP are not considered sensitive on privacy
grounds because ACP nodes are not expected to be end-user hosts,
and therefore ACP addresses do not represent end users or groups
of end users. All ACP nodes are in one (potentially federated)
administrative domain. For ACP traffic, the nodes are assumed to
be either candidate hosts or transit nodes. There are no transit
nodes with fewer privileges to know the identity of other hosts in
the ACP. Therefore, ACP addresses do not need to be pseudorandom
as discussed in "Security and Privacy Considerations for IPv6
Address Generation Mechanisms" [RFC7721]. Because they are not
propagated to untrusted (non-ACP) nodes and stay within a domain
(of trust), we also do not consider them to be subject to scanning
attacks.
The ACP is based exclusively on IPv6 addressing for a variety of
reasons:
* Simplicity, reliability, and scale: if other network-layer
protocols were supported, each would have to have its own set of
security associations, routing table, and process, etc.
* Autonomic functions do not require IPv4: autonomic functions and
autonomic service agents are new concepts. They can be
exclusively built on IPv6 from day one. There is no need for
backward compatibility.
* OAM protocols do not require IPv4: the ACP may carry OAM
protocols. All relevant protocols (SNMP, TFTP, SSH, SCP, RADIUS,
Diameter, NETCONF, etc.) are available in IPv6. See also
[RFC8368] for how ACP could be made to interoperate with IPv4-only
OAM.
Further explanation about the addressing and routing-related reasons
for the choice of the autonomous ACP addressing can be found in
Section 6.13.5.1.
6.11.2. The ACP Addressing Base Scheme
The ULA addressing base scheme for ACP nodes has the following
format:
8 40 2 78
+--+-------------------------+------+------------------------------+
|fd| hash(routing-subdomain) | Type | (sub-scheme) |
+--+-------------------------+------+------------------------------+
Figure 9: ACP Addressing Base Scheme
The first 48 bits follow the ULA scheme as defined in [RFC4193], to
which a Type field is added.
fd: Identifies a locally defined ULA address.
hash(routing-subdomain): The 40-bit ULA Global ID (a term from
[RFC4193]) for ACP addresses carried in the acp-node-name in the
ACP certificates are the first 40 bits of the SHA-256 hash of the
routing-subdomain from the same acp-node-name. In the example of
Section 6.2.2, the routing-subdomain is
"area51.research.acp.example.com", and the 40-bit ULA Global ID is
89b714f3db.
When creating a new routing-subdomain for an existing Autonomic
Network, it MUST be ensured that rsub is selected so the resulting
hash of the routing-subdomain does not collide with the hash of
any preexisting routing-subdomains of the Autonomic Network. This
ensures that ACP addresses created by registrars for different
routing subdomains do not collide with each other.
To allow for extensibility, the fact that the ULA Global ID is a
hash of the routing-subdomain SHOULD NOT be assumed by any ACP
node during normal operations. The hash function is only executed
during the creation of the certificate. If BRSKI is used, then
the BRSKI registrar will create the acp-node-name in response to
the EST Certificate Signing Request (CSR) Attributes Request
message sent by the pledge.
Establishing connectivity between different ACPs (different acp-
domain-names) is outside the scope of this specification. If it
is being done through future extensions, then the rsub of all
routing-subdomains across those Autonomic Networks needs to be
selected so that the resulting routing-subdomain hashes do not
collide. For example, a large cooperation with its own private TA
may want to create different Autonomic Networks that initially do
not connect but where the option to do so should be kept open.
When taking this possibility into account, it is always easy to
select rsub so that no collisions happen.
Type: This field allows different addressing sub-schemes. This
addresses the "upgradability" requirement. Assignment of types
for this field will be maintained by IANA.
(sub-scheme): The sub-scheme may imply a range or set of addresses
assigned to the node. This is called the ACP address range/set
and explained in each sub-scheme.
Please refer to Section 6.11.7 and Appendix A.1 for further
explanations for why the following addressing sub-schemes are used
and why multiple are necessary.
The following summarizes the addressing sub-schemes:
+======+==============+=======+=====+=========+========+
| Type | Name | F-bit | Z | V-bits | Prefix |
+======+==============+=======+=====+=========+========+
| 0 | ACP-Zone | N/A | 0 | 1 bit | /127 |
+------+--------------+-------+-----+---------+--------+
| 0 | ACP-Manual | N/A | 1 | N/A | /64 |
+------+--------------+-------+-----+---------+--------+
| 1 | ACP-Vlong-8 | 0 | N/A | 8 bits | /120 |
+------+--------------+-------+-----+---------+--------+
| 1 | ACP-Vlong-16 | 1 | N/A | 16 bits | /112 |
+------+--------------+-------+-----+---------+--------+
| 2 | Reserved / For future definition/allocation |
+------+-----------------------------------------------+
| 3 | Reserved / For future definition/allocation |
+------+-----------------------------------------------+
Table 1: Addressing Sub-Schemes
The F-bit (format bit, Section 6.11.5) and Z (Section 6.11.4) are two
encoding fields that are explained in the sections covering the sub-
schemes that use them. V-bits is the number of bits of addresses
allocated to the ACP node. Prefix is the prefix that the ACP node is
announcing into RPL.
6.11.3. ACP Zone Addressing Sub-Scheme (ACP-Zone)
This sub-scheme is used when the Type field of the base scheme is 0
and the Z bit is 0.
64 64
+-----------------+---+---------++-----------------------------+---+
| (base scheme) | Z | Zone-ID || Node-ID |
| | | || Registrar-ID | Node-Number| V |
+-----------------+---+---------++--------------+--------------+---+
50 1 13 48 15 1
Figure 10: ACP Zone Addressing Sub-Scheme
The fields are defined as follows:
Type: MUST be 0.
Z: MUST be 0.
Zone-ID: A value for a network zone.
Node-ID: A unique value for each node.
The 64-bit Node-ID must be unique across the ACP domain for each
node. It is derived and composed as follows:
Registrar-ID (48 bits): A number unique inside the domain
identifying the ACP registrar that assigned the Node-ID to the
node. One or more domain-wide unique identifiers of the ACP
registrar can be used for this purpose. See Section 6.11.7.2.
Node-Number: A number to make the Node-ID unique. This can be
sequentially assigned by the ACP registrar owning the
Registrar-ID.
V (1 bit): Virtualization bit:
0: Indicates the ACP itself ("ACP node base system)
1: Indicates the optional "host" context on the ACP node (see
below).
In the Zone Addressing Sub-Scheme, the ACP address in the certificate
has V field as all zero bits.
The ACP address set of the node includes addresses with any Zone-ID
value and any V value. Therefore, no two nodes in the same ACP and
the same hash(routing-subdomain) can have the same Node-ID with the
Zone Addressing Sub-Scheme, for example, by differing only in their
Zone-ID.
The Virtualization bit in this sub-scheme allows the easy addition of
the ACP as a component to existing systems without causing problems
in the port number space between the services in the ACP and the
existing system. V=0 is the ACP router (autonomic node base system),
V=1 is the host with preexisting transport endpoints on it that could
collide with the transport endpoints used by the ACP router. The ACP
host could, for example, have a P2P (peer-to-peer) virtual interface
with the V=0 address as its router to the ACP. Depending on the
software design of ASAs, which is outside the scope of this
specification, they may use the V=0 or V=1 address.
The location of the V bit(s) at the end of the address allows the
announcement of a single prefix for each ACP node. For example, in a
network with 20,000 ACP nodes, this avoids 20,000 additional routes
in the routing table.
It is RECOMMENDED that only Zone-ID 0 is used unless it is meant to
be used in conjunction with operational practices for partial or
incremental adoption of the ACP as described in Section 9.4.
Note: Zones and Zone-ID as defined here are not related to zones or
zone_id defined in "IPv6 Scoped Address Architecture" [RFC4007]. ACP
zone addresses are not scoped (i.e., reachable only from within a
zone as defined by [RFC4007]) but are reachable across the whole ACP.
A zone_id is a zone index that has only local significance on a node
[RFC4007], whereas an ACP Zone-ID is an identifier for an ACP zone
that is unique across that ACP.
6.11.4. ACP Manual Addressing Sub-Scheme (ACP-Manual)
This sub-scheme is used when the Type field of the base scheme is 0
and the Z bit is 1.
64 64
+---------------------+---+----------++-----------------------------+
| (base scheme) | Z | Subnet-ID|| Interface Identifier |
+---------------------+---+----------++-----------------------------+
50 1 13
Figure 11: ACP Manual Addressing Sub-Scheme
The fields are defined as follows:
Type: MUST be 0.
Z: MUST be 1.
Subnet-ID: Configured subnet identifier.
Interface Identifier: Interface identifier according to [RFC4291].
This sub-scheme is meant for the "manual" allocation to subnets where
the other addressing schemes cannot be used. The primary use case is
for assignment to ACP connect subnets (see Section 8.1.1).
"Manual" means that allocations of the Subnet-ID need to be done with
preexisting, non-autonomic mechanisms. Every subnet that uses this
addressing sub-scheme needs to use a unique Subnet-ID (unless some
anycast setup is done).
The Z bit field was added to distinguish between the Zone Addressing
Sub-Scheme and the Manual Addressing Sub-Scheme without requiring one
more bit in the base scheme and therefore allowing for the Vlong
Addressing Sub-Scheme (described in Section 6.11.5) to have one more
bit available.
The Manual Addressing Sub-Scheme addresses SHOULD NOT be used in ACP
certificates. Any node capable of building ACP secure channels and
is permitted by registrar policy to participate in building ACP
secure channels SHOULD receive an ACP address (prefix) from one of
the other ACP addressing sub-schemes. A node that cannot or is not
permitted to participate in ACP secure channels can connect to the
ACP via ACP connect interfaces of ACP edge nodes (see Section 8.1)
without setting up an ACP secure channel. Its ACP certificate MUST
omit the acp-address field to indicate that its ACP certificate is
only usable for non-ACP secure channel authentication, such as end-
to-end transport connections across the ACP or data plane.
Address management of ACP connect subnets is done using traditional
assignment methods and existing IPv6 protocols. See Section 8.1.3
for details. Therefore, the notion of /V-bits multiple addresses
assigned to the ACP nodes does not apply to this sub-scheme.
6.11.5. ACP Vlong Addressing Sub-Scheme (ACP-Vlong-8/ACP-Vlong-16)
This addressing sub-scheme is used when the Type field of the base
scheme is 1.
50 78
+---------------------++-----------------------------+----------+
| (base scheme) || Node-ID |
| || Registrar-ID |F| Node-Number| V |
+---------------------++--------------+--------------+----------+
50 46 1 23/15 8/16
Figure 12: ACP Vlong Addressing Sub-Scheme
This addressing sub-scheme foregoes the Zone-ID field
(Section 6.11.3) to allow for larger, flatter routed networks (e.g.,
as in IoT) with 8,421,376 Node-Numbers (2^23 + 2^15). It also allows
for up to 2^16 (i.e., 65,536) different virtualized addresses within
a node, which could be used to address individual software components
in an ACP node.
The fields are the same as in the Zone Addressing Sub-Scheme
(Section 6.11.3) with the following refinements:
F: Format bit. This bit determines the format of the subsequent
bits.
V: Virtualization bit: this is a field that is either 8 or 16 bits.
For F=0, it is 8 bits, for F=1 it is 16 bits. The V-bits are
assigned by the ACP node. In the ACP certificate's ACP address
(Section 6.2.2), the V-bits are always set to 0.
Registrar-ID: To maximize Node-Number and V, the Registrar-ID is
reduced to 46 bits. One or more domain-wide unique identifiers of
the ACP registrar can be used for this purpose. See
Section 6.11.7.2.
Node-Number: The Node-Number is unique to each ACP node. There are
two formats for the Node-Number. When F=0, the Node-Number is 23
bits, for F=1, it is 15 bits. Each format of Node-Number is
considered to be in a unique number space.
The F=0 bit format addresses are intended to be used for "general
purpose" ACP nodes that would potentially have a limited number (less
than 256) of clients (ASA and/or autonomic functions or legacy
services) of the ACP that require separate V(irtual) addresses.
The F=1 bit Node-Numbers are intended for ACP nodes that are ACP edge
nodes (see Section 8.1.1) or that have a large number of clients
requiring separate V(irtual) addresses, for example, large SDN
controllers with container modular software architecture (see
Section 8.1.2).
In the Vlong Addressing Sub-Scheme, the ACP address in the
certificate has all V field bits as zero. The ACP address set for
the node includes any V value.
6.11.6. Other ACP Addressing Sub-Schemes
Before further addressing sub-schemes are defined, experience with
the schemes defined here should be collected. The schemes defined in
this document have been devised to allow hopefully a sufficiently
flexible setup of ACPs for a variety of situations. These reasons
also lead to the fairly liberal use of address space: the Zone
Addressing Sub-Scheme is intended to enable optimized routing in
large networks by reserving bits for Zone-IDs. The Vlong Addressing
Sub-Scheme enables the allocation of 8/16-bit of addresses inside
individual ACP nodes. Both address spaces allow distributed,
uncoordinated allocation of node addresses by reserving bits for the
Registrar-ID field in the address.
6.11.7. ACP Registrars
ACP registrars are responsible for enrolling candidate ACP nodes with
ACP certificates and associated trust anchor(s). They are also
responsible for including an acp-node-name field in the ACP
certificate. This field carries the ACP domain name and the ACP
node's ACP address prefix. This address prefix is intended to
persist unchanged through the lifetime of the ACP node.
Because of the ACP addressing sub-schemes, an ACP domain can have
multiple distributed ACP registrars that do not need to coordinate
for address assignment. ACP registrars can also be sub-CAs, in which
case they can also assign ACP certificates without dependencies
against a (shared) TA (except during renewals of their own
certificates).
ACP registrars are PKI registration authorities (RA) enhanced with
the handling of the ACP certificate-specific fields. They request
certificates for ACP nodes from a CA through any appropriate
mechanism (out of scope in this document, but this mechanism is
required to be BRSKI for ANI registrars). Only nodes that are
trusted to be compliant with the registrar requirements described in
this section can be given the necessary credentials to perform this
RA function, such as the credential for the ACP registrar to connect
to the CA as a registrar.
6.11.7.1. Use of BRSKI or Other Mechanisms or Protocols
Any protocols or mechanisms may be used by ACP registrars as long as
the resulting ACP certificate and TA certificate(s) can be used by
other domain members to perform the ACP domain membership check
described in Section 6.2.3, and the acp-node-name meets the ACP
addressing requirements described in the next three sections.
An ACP registrar could be a person deciding whether to enroll a
candidate ACP node and then orchestrating the enrollment of the ACP
certificate and associated TA, using command line or web-based
commands on the candidate ACP node and TA to generate and sign the
ACP certificate and configure certificate and TA onto the node.
The only currently defined protocol for ACP registrars is BRSKI
[RFC8995]. When BRSKI is used, the ACP nodes are called ANI nodes,
and the ACP registrars are called BRSKI or ANI registrars. The BRSKI
specification does not define the handling of the acp-node-name field
because the rules do not depend on BRSKI but apply equally to any
protocols or mechanisms that an ACP registrar may use.
6.11.7.2. Unique Address/Prefix Allocation
ACP registrars MUST NOT allocate ACP address prefixes to ACP nodes
via the acp-node-name that would collide with the ACP address
prefixes of other ACP nodes in the same ACP domain. This includes
both prefixes allocated by the same ACP registrar to different ACP
nodes as well as prefixes allocated by other ACP registrars for the
same ACP domain.
To support such unique address allocation, an ACP registrar MUST have
one or more 46-bit identifiers, called the Registrar-ID, that are
unique across the ACP domain. Allocation of Registrar-ID(s) to an
ACP registrar can happen through OAM mechanisms in conjunction with
some database and/or allocation orchestration.
ACP registrars running on physical devices with known globally unique
EUI-48 MAC address(es) (EUI stands for "Extended Unique Identifier")
can use the lower 46 bits of those address(es) as unique Registrar-
IDs without requiring any external signaling and/or configuration
(the upper two bits, V and U, are not uniquely assigned but are
functional). This approach is attractive for distributed, non-
centrally administered, lightweight ACP registrar implementations.
There is no mechanism to deduce from a MAC address itself whether it
is actually uniquely assigned. Implementations need to consult
additional offline information before making this assumption, for
example, by knowing that a particular physical product or Network
Interface Controller (NIC) chip is guaranteed to use globally unique
assigned EUI-48 MAC address(es).
When the candidate ACP device (called pledge in BRSKI) is to be
enrolled into an ACP domain, the ACP registrar needs to allocate a
unique ACP address to the node and ensure that the ACP certificate
gets an acp-node-name field (Section 6.2.2) with the appropriate
information: ACP domain name, ACP address, and so on. If the ACP
registrar uses BRSKI, it signals the ACP acp-node-name field to the
pledge via EST CSR Attributes (see [RFC8995], Section 5.9.2, "EST CSR
Attributes").
6.11.7.3. Addressing Sub-Scheme Policies
The ACP registrar selects for the candidate ACP node a unique address
prefix from an appropriate ACP addressing sub-scheme, either a Zone
Addressing Sub-Scheme prefix (see Section 6.11.3), or a Vlong
Addressing Sub-Scheme prefix (see Section 6.11.5). The assigned ACP
address prefix encoded in the acp-node-name field of the ACP
certificate indicates to the ACP node its ACP address information.
The addressing sub-scheme indicates the prefix length: /127 for the
Zone Addressing Sub-Scheme, /120 or /112 for the Vlong Addressing
Sub-Scheme. The first address of the prefix is the ACP address. All
other addresses in the prefix are for other uses by the ACP node as
described in the Zone Addressing Sub-Scheme and Vlong Addressing Sub-
Scheme sections. The ACP address prefix itself is then signaled by
the ACP node into the ACP routing protocol (see Section 6.12) to
establish IPv6 reachability across the ACP.
The choice of addressing sub-scheme and prefix length in the Vlong
Addressing Sub-Scheme is subject to ACP registrar policy. It could
be an ACP domain-wide policy, or a per ACP node or per ACP node type
policy. For example, in BRSKI, the ACP registrar is aware of the
IDevID certificate of the candidate ACP node, which typically
contains a "serialNumber" attribute in the subject field
distinguished name encoding that often indicates the node's vendor
and device type, and it can be used to drive a policy for selecting
an appropriate addressing sub-scheme for the (class of) node(s).
ACP registrars SHOULD default to allocating Zone Addressing Sub-
Scheme addresses with Zone-ID 0.
ACP registrars that are aware of the IDevID certificate of a
candidate ACP device SHOULD be able to choose the Zone vs. Vlong
Addressing Sub-Scheme for ACP nodes based on the "serialNumber"
attribute [X.520] in the subject field distinguished name encoding of
the IDevID certificate, for example, by the PID (Product Identifier)
part, which identifies the product type, or by the complete
"serialNumber". The PID, for example, could identify nodes that
allow for specialized ASA requiring multiple addresses or for non-
autonomic virtual machines (VMs) for services, and those nodes could
receive Vlong Addressing Sub-Scheme ACP addresses.
In a simple allocation scheme, an ACP registrar remembers
persistently across reboots its currently used Registrar-ID and, for
each addressing scheme (Zone with Zone-ID 0, Vlong with /112, Vlong
with /120), the next Node-Number available for allocation, and it
increases the next Node-Number during successful enrollment of an ACP
node. In this simple allocation scheme, the ACP registrar would not
recycle ACP address prefixes from ACP nodes that are no longer used.
If allocated addresses cannot be remembered by registrars, then it is
necessary either to use a new value for the Register-ID field in the
ACP addresses or to determine allocated ACP addresses by determining
the addresses of reachable ACP nodes, which is not necessarily the
set of all ACP nodes. Untracked ACP addresses can be reclaimed by
revoking or not renewing their certificates and instead handing out
new certificates with new addresses (for example, with a new
Registrar-ID value). Note that such strategies may require
coordination amongst registrars.
6.11.7.4. Address/Prefix Persistence
When an ACP certificate is renewed or rekeyed via EST or other
mechanisms, the ACP address/prefix in the acp-node-name field MUST be
maintained unless security issues or violations of the unique address
assignment requirements exist or are suspected by the ACP registrar.
ACP address information SHOULD be maintained even when the renewing
and/or rekeying ACP registrar is not the same as the one that
enrolled the prior ACP certificate. See Section 9.2.4 for an
example.
ACP address information SHOULD also be maintained even after an ACP
certificate expires or fails. See Section 6.2.5.5 and
Section 6.2.5.6.
6.11.7.5. Further Details
Section 9.2 discusses further informative details of ACP registrars:
needed interactions, required parameters, certificate renewal and
limitations, use of sub-CAs on registrars, and centralized policy
control.
6.12. Routing in the ACP
Once ULA addresses are set up, all autonomic entities should run a
routing protocol within the ACP context. This routing protocol
distributes the ULA created in the previous section for reachability.
The use of the ACP-specific context eliminates the probable clash
with data plane routing tables and also secures the ACP from
interference from configuration mismatch or incorrect routing
updates.
The establishment of the routing plane and its parameters are
automatic and strictly within the confines of the ACP. Therefore, no
explicit configuration is required.
All routing updates are automatically secured in transit as the
channels of the ACP are encrypted, and this routing runs only inside
the ACP.
The routing protocol inside the ACP is RPL [RFC6550]. See
Appendix A.4 for more details on the choice of RPL.
RPL adjacencies are set up across all ACP channels in the same domain
including all its routing subdomains. See Appendix A.6 for more
details.
6.12.1. ACP RPL Profile
The following is a description of the RPL profile that ACP nodes need
to support by default. The format of this section is derived from
[ROLL-APPLICABILITY].
6.12.1.1. Overview
RPL Packet Information (RPI), defined in [RFC6550], Section 11.2,
defines the data packet artifacts required or beneficial in the
forwarding of packets routed by RPL. This profile does not use RPI
for better compatibility with accelerated hardware forwarding planes,
which most often do not support the Hop-by-Hop headers used for RPI,
but also to avoid the overhead of the RPI header on the wire and cost
of adding and/or removing them.
6.12.1.1.1. Single Instance
To avoid the need for RPI, the ACP RPL profile uses a simple routing/
forwarding table based on destination prefix. To achieve this, the
profile uses only one RPL instanceID. This single instanceID can
contain only one Destination-Oriented Directed Acyclic Graph (DODAG),
and the routing/forwarding table can therefore only calculate a
single class of service ("best effort towards the primary NOC/root")
and cannot create optimized routing paths to accomplish latency or
energy goals between any two nodes.
This choice is a compromise. Consider a network that has multiple
NOCs in different locations. Only one NOC will become the DODAG
root. Traffic to and from other NOCs has to be sent through the
DODAG (shortest path tree) rooted in the primary NOC. Depending on
topology, this can be an annoyance from a point of view of latency or
minimizing network path resources, but this is deemed to be
acceptable given how ACP traffic is "only" network management/control
traffic. See Appendix A.9.4 for more details.
Using a single instanceID/DODAG does not introduce a single point of
failure, as the DODAG will reconfigure itself when it detects data
plane forwarding failures, including choosing a different root when
the primary one fails.
The benefit of this profile, especially compared to other IGPs, is
that it does not calculate routes for nodes reachable through the
same interface as the DODAG root. This RPL profile can therefore
scale to a much larger number of ACP nodes in the same amount of
computation and memory than other routing protocols, especially on
nodes that are leafs of the topology or those close to those leafs.
6.12.1.1.2. Reconvergence
In RPL profiles where RPI (see Section 6.12.1.13) is present, it is
also used to trigger reconvergence when misrouted, for example,
looping packets, which are recognized because of their RPI data.
This helps to minimize RPL signaling traffic, especially in networks
without stable topology and slow links.
The ACP RPL profile instead relies on quickly reconverging the DODAG
by recognizing link state change (down/up) and triggering
reconvergence signaling as described in Section 6.12.1.7. Since
links in the ACP are assumed to be mostly reliable (or have link-
layer protection against loss) and because there is no stretch
according to Section 6.12.1.7, loops caused by loss of RPL signaling
packets should be exceedingly rare.
In addition, there are a variety of mechanisms possible in RPL to
further avoid temporary loops that are RECOMMENDED to be used for the
ACP RPL profile: DODAG Information Objects (DIOs) SHOULD be sent two
or three times to inform children when losing the last parent. The
technique in [RFC6550], Section 8.2.2.6 (Detaching) SHOULD be favored
over that in Section 8.2.2.5 (Poisoning) because it allows local
connectivity. Nodes SHOULD select more than one parent, at least
three if possible, and send Destination Advertisement Objects (DAOs)
to all of them in parallel.
Additionally, failed ACP tunnels can be quickly discovered through
the secure channel protocol mechanisms such as IKEv2 dead peer
detection. This can function as a replacement for a Low-power and
Lossy Network's (LLN's) Expected Transmission Count (ETX) feature,
which is not used in this profile. A failure of an ACP tunnel should
immediately signal the RPL control plane to pick a different parent.
6.12.1.2. RPL Instances
There is a single RPL instance. The default RPLInstanceID is 0.
6.12.1.3. Storing vs. Non-Storing Mode
The RPL Mode of Operation (MOP) MUST support mode 2, "Storing Mode of
Operations with no multicast support". Implementations MAY support
mode 3 ("... with multicast support") as that is a superset of mode
2. Note: Root indicates mode in DIO flow.
6.12.1.4. DAO Policy
The DAO policy is proactive, aggressive DAO state maintenance:
* Use the 'K' flag in unsolicited DAO to indicate change from
previous information (to require DAO-ACK).
* Retry such DAO DAO-RETRIES(3) times with DAO-ACK_TIME_OUT(256ms)
in between.
6.12.1.5. Path Metrics
Use Hop Count according to "Routing Metrics Used for Path Calculation
in Low-Power and Lossy Networks" [RFC6551]. Note that this is solely
for diagnostic purposes as it is not used by the Objective Function.
6.12.1.6. Objective Function
Objective Function (OF): Use Objective Function Zero (OF0)
("Objective Function Zero for the Routing Protocol for Low-Power
and Lossy Networks (RPL)" [RFC6552]). Metric containers are not
used.
rank_factor: Derived from link speed: if less than or equal to 100
Mbps, LOW_SPEED_FACTOR(5), else HIGH_SPEED_FACTOR(1).
This is a simple rank differentiation between typical "low speed"
or IoT links that commonly max out at 100 Mbps and typical
infrastructure links with speeds of 1 Gbps or higher. Given how
the path selection for the ACP focuses only on reachability but
not on path cost optimization, no attempts at finer-grained path
optimization are made.
6.12.1.7. DODAG Repair
Global Repair: We assume stable links and ranks (metrics), so there
is no need to periodically rebuild the DODAG. The DODAG version
is only incremented under catastrophic events (e.g.,
administrative action).
Local Repair: As soon as link breakage is detected, the ACP node
sends a No-Path DAO for all the targets that were reachable only
via this link. As soon as link repair is detected, the ACP node
validates if this link provides a better parent. If so, a new
rank is computed by the ACP node, and it sends a new DIO that
advertises the new rank. Then it sends a DAO with a new path
sequence about itself.
When using ACP multi-access virtual interfaces, local repair can
be triggered directly by peer breakage, see Section 6.13.5.2.2.
stretch_rank: None provided ("not stretched").
Data-Path Validation: Not used.
Trickle: Not used.
6.12.1.8. Multicast
Multicast is not used yet, but it is possible because of the selected
mode of operations.
6.12.1.9. Security
RPL security [RFC6550] is not used, and ACP security is substituted.
Because the ACP links already include provisions for confidentiality
and integrity protection, their usage at the RPL layer would be
redundant, and so RPL security is not used.
6.12.1.10. P2P Communications
Not used.
6.12.1.11. IPv6 Address Configuration
Every ACP node (RPL node) announces an IPv6 prefix covering the
addresses assigned to the ACP node via the AcpNodeName. The prefix
length depends on the addressing sub-scheme of the acp-address, /127
for the Zone Addressing Sub-Scheme and /112 or /120 for the Vlong
Addressing Sub-Scheme. See Section 6.11 for more details.
Every ACP node MUST install a black hole route (also known as a null
route) if there are unused parts of the ACP address space assigned to
the ACP node via its AcpNodeName. This is superseded by longer
prefixes assigned to interfaces for the address space actually used
by the node. For example, when the node has an ACP-Vlong-8 address
space, it installs a /120 black hole route. If it then only uses the
ACP address (first address from the space), for example, it would
assign that address via a /128 address prefix to the ACP loopback
interface (see Section 6.13.5.1). None of those longer prefixes are
announced into RPL.
For ACP-Manual address prefixes configured on an ACP node, for
example, for ACP connect subnets (see Section 8.1.1), the node
announces the /64 subnet prefix.
6.12.1.12. Administrative Parameters
Administrative Preference ([RFC6550], Section 3.2.6 --to become
root): The preference is indicated in the DODAGPreference field of
DIO message.
Explicitly configured "root": 0b100
ACP registrar (default): 0b011
ACP connect (non-registrar): 0b010
Default: 0b001
6.12.1.13. RPL Packet Information
RPI is not required in the ACP RPL profile for the following reasons.
One RPI option is the RPL Source Routing Header (SRH) ("An IPv6
Routing Header for Source Routes with the Routing Protocol for
Low-Power and Lossy Networks (RPL)" [RFC6554]), which is not
necessary because the ACP RPL profile uses storing mode where each
hop has the necessary next-hop forwarding information.
The simpler RPL Option header "The Routing Protocol for Low-Power and
Lossy Networks (RPL) Option for Carrying RPL Information in
Data-Plane Datagrams" [RFC6553] is also not necessary in this
profile, because it uses a single RPL instance and data-path
validation is also not used.
6.12.1.14. Unknown Destinations
Because RPL minimizes the size of the routing and forwarding table,
prefixes reachable through the same interface as the RPL root are not
known on every ACP node. Therefore, traffic to unknown destination
addresses can only be discovered at the RPL root. The RPL root
SHOULD have attach-safe mechanisms to operationally discover and log
such packets.
As this requirement places additional constraints on the data plane
functionality of the RPL root, it does not apply to "normal" nodes
that are not configured to have special functionality (i.e., the
administrative parameter from Section 6.12.1.12 has value 0b001). If
the ACP network is degraded to the point where there are no nodes
that could be configured as root, registrar, or ACP connect nodes, it
is possible that the RPL root (and thus the ACP as a whole) would be
unable to detect traffic to unknown destinations. However, in the
absence of nodes with administrative preference other than 0b001,
there is also unlikely to be a way to get diagnostic information out
of the ACP, so detection of traffic to unknown destinations would not
be actionable anyway.
6.13. General ACP Considerations
Since channels are established between adjacent neighbors by default,
the resulting overlay network does hop-by-hop encryption. Each node
decrypts incoming traffic from the ACP and encrypts outgoing traffic
to its neighbors in the ACP. Routing is discussed in Section 6.12.
6.13.1. Performance
There are no performance requirements for ACP implementations defined
in this document because the performance requirements depend on the
intended use case. It is expected that a fully autonomic node with a
wide range of ASA can require high forwarding plane performance in
the ACP, for example, for telemetry. Implementations of ACP that
solely support traditional or SDN-style use cases can benefit from
ACP at lower performance, especially if the ACP is used only for
critical operations, e.g., when the data plane is not available. The
design of the ACP as specified in this document is intended to
support a wide range of performance options: it is intended to allow
software-only implementations at potentially low performance, but the
design can also support high-performance options. See [RFC8368] for
more details.
6.13.2. Addressing of Secure Channels
In order to be independent of the data plane routing and addressing,
the ACP secure channels discovered via GRASP use IPv6 link-local
addresses between adjacent neighbors. Note: Section 8.2 specifies
extensions in which secure channels are configured tunnels operating
over the data plane, so those secure channels cannot be independent
of the data plane.
To avoid impacting the operations of the IPv6 (link-local) interface/
address used for ACP channels when configuring the data plane,
appropriate implementation considerations are required. If the IPv6
interface/link-local address is shared with the data plane, it needs
to be impossible to unconfigure and/or disable it through
configuration. Instead of sharing the IPv6 interface/link-local
address, a separate (virtual) interface with a separate IPv6 link-
local address can be used. For example, the ACP interface could be
run over a separate MAC address of an underlying L2 (Ethernet)
interface. For more details and options, see Appendix A.9.2.
Note that other (nonideal) implementation choices may introduce
additional, undesired dependencies against the data plane, for
example, shared code and configuration of the secure channel
protocols (IPsec and/or DTLS).
6.13.3. MTU
The MTU for ACP secure channels MUST be derived locally from the
underlying link MTU minus the secure channel encapsulation overhead.
ACP secure channel protocols do not need to perform MTU discovery
because they are built across L2 adjacencies: the MTUs on both sides
connecting to the L2 connection are assumed to be consistent.
Extensions to ACP where the ACP is, for example, tunneled need to
consider how to guarantee MTU consistency. This is an issue of
tunnels, not an issue of running the ACP across a tunnel. Transport
stacks running across ACP can perform normal PMTUD (Path MTU
Discovery). Because the ACP is meant to prioritize reliability over
performance, they MAY opt to only expect IPv6 minimum MTU (1280
octets) to avoid running into PMTUD implementation bugs or underlying
link MTU mismatch problems.
6.13.4. Multiple Links between Nodes
If two nodes are connected via several links, the ACP SHOULD be
established across every link, but it is possible to establish the
ACP only on a subset of links. Having an ACP channel on every link
has a number of advantages, for example, it allows for a faster
failover in case of link failure, and it reflects the physical
topology more closely. Using a subset of links (for example, a
single link), reduces resource consumption on the node because state
needs to be kept per ACP channel. The negotiation scheme explained
in Section 6.6 allows the Decider (the node with the higher ACP
address) to drop all but the desired ACP channels to the Follower,
and the Follower will not retry to build these secure channels from
its side unless the Decider appears with a previously unknown GRASP
announcement (e.g., on a different link or with a different address
announced in GRASP).
6.13.5. ACP Interfaces
Conceptually, the ACP VRF has two types of interfaces: the "ACP
loopback interface(s)" to which the ACP ULA address(es) are assigned
and the "ACP virtual interfaces" that are mapped to the ACP secure
channels.
6.13.5.1. ACP Loopback Interfaces
For autonomous operations of the ACP, as described in Section 6 and
Section 7, the ACP node uses the first address from the N bit ACP
prefix assigned to the node. N = (128 - number of Vbits of the ACP
address). This address is assigned with an address prefix of N or
larger to a loopback interface.
Other addresses from the prefix can be used by the ACP of the node as
desired. The autonomous operations of the ACP do not require
additional global-scope IPv6 addresses, they are instead intended for
ASA or non-autonomous functions. Components of the ACP that are not
fully autonomic, such as ACP connect interfaces (see Figure 14), may
also introduce additional global-scope IPv6 addresses on other types
of interfaces to the ACP.
The use of loopback interfaces for global-scope addresses is common
operational configuration practice on routers, for example, in
Internal BGP (IBGP) connections since BGP4 (see "A Border Gateway
Protocol 4 (BGP-4)" [RFC1654]) or earlier. The ACP adopts and
automates this operational practice.
A loopback interface for use with the ACP as described above is an
interface that behaves according to Section 4 of "Default Address
Selection for Internet Protocol Version 6 (IPv6)" [RFC6724],
paragraph 2. Packets sent by the host of the node from the loopback
interface behave as if they are looped back by the interface so that
they look as if they originated from the loopback interface, are then
received by the node and forwarded by it towards the destination.
The term "loopback only" indicates this behavior, but not the actual
name of the interface type chosen in an actual implementation. A
loopback interface for use with the ACP can be a virtual and/or
software construct without any associated hardware, or it can be a
hardware interface operating in loopback mode.
A loopback interface used for the ACP MUST NOT have connectivity to
other nodes.
The following list reviews the reasons for the choice of loopback
addresses for ACP addresses, which is based on the IPv6 address
architecture and common challenges:
1. IPv6 addresses are assigned to interfaces, not nodes. IPv6
continues the IPv4 model that a subnet prefix is associated with
one link, see Section 2.1 of "IP Version 6 Addressing
Architecture" [RFC4291].
2. IPv6 implementations commonly do not allow assignment of the same
IPv6 global-scope address in the same VRF to more than one
interface.
3. Global-scope addresses assigned to interfaces that connect to
other nodes (external interfaces) may not be stable addresses for
communications because any such interface could fail due to
reasons external to the node. This could render the addresses
assigned to that interface unusable.
4. If failure of the subnet does not bring down the interface and
make the addresses unusable, it could result in unreachability of
the address because the shortest path to the node might go
through one of the other nodes on the same subnet, which could
equally consider the subnet to be operational even though it is
not.
5. Many OAM service implementations on routers cannot deal with more
than one peer address, often because they already expect that a
single loopback address can be used, especially to provide a
stable address under failure of external interfaces or links.
6. Even when an application supports multiple addresses to a peer,
it can only use one address at a time for a connection with the
most widely deployed transport protocols, TCP and UDP. While
"TCP Extensions for Multipath Operation with Multiple Addresses"
[RFC6824]/[RFC8684] solves this problem, it is not widely adopted
by implementations of router OAM services.
7. To completely autonomously assign global-scope addresses to
subnets connecting to other nodes, it would be necessary for
every node to have an amount of prefix address space on the order
of the maximum number of subnets that the node could connect to,
and then the node would have to negotiate with adjacent nodes
across those subnets which address space to use for each subnet.
8. Using global-scope addresses for subnets between nodes is
unnecessary if those subnets only connect routers, such as ACP
secure channels, because they can communicate to remote nodes via
their global-scope loopback addresses. Using global-scope
addresses for those external subnets is therefore wasteful for
the address space and also unnecessarily increases the size of
the routing and forwarding tables, which, especially for the ACP,
is highly undesirable because it should attempt to minimize the
per-node overhead of the ACP VRF.
9. For all these reasons, the ACP addressing sub-schemes do not
consider ACP addresses for subnets connecting ACP nodes.
Note that "Segment Routing Architecture" [RFC8402] introduces the
term Node-SID to refer to IGP prefix segments that identify a
specific router, for example, on a loopback interface. An ACP
loopback address prefix may similarly be called an ACP Node
Identifier.
6.13.5.2. ACP Virtual Interfaces
Any ACP secure channel to another ACP node is mapped to ACP virtual
interfaces in one of the following ways. This is independent of the
chosen secure channel protocol (IPsec, DTLS, or other future
protocol, either standardized or not).
Note that all the considerations described here assume point-to-point
secure channel associations. Mapping multiparty secure channel
associations, such as "The Group Domain of Interpretation" [RFC6407],
is out of scope.
6.13.5.2.1. ACP Point-to-Point Virtual Interfaces
In this option, each ACP secure channel is mapped to a separate
point-to-point ACP virtual interface. If a physical subnet has more
than two ACP-capable nodes (in the same domain), this implementation
approach will lead to a full mesh of ACP virtual interfaces between
them.
When the secure channel protocol determines a peer to be dead, this
SHOULD result in indicating link breakage to trigger RPL DODAG
repair, see Section 6.12.1.7.
6.13.5.2.2. ACP Multi-Access Virtual Interfaces
In a more advanced implementation approach, the ACP will construct a
single multi-access ACP virtual interface for all ACP secure channels
to ACP-capable nodes reachable across the same underlying (physical)
subnet. IPv6 link-local multicast packets sent to an ACP multi-
access virtual interface are replicated to every ACP secure channel
mapped to the ACP multi-access virtual interface. IPv6 unicast
packets sent to an ACP multi-access virtual interface are sent to the
ACP secure channel that belongs to the ACP neighbor that is the next
hop in the ACP forwarding table entry used to reach the packets'
destination address.
When the secure channel protocol determines that a peer is dead for a
secure channel mapped to an ACP multi-access virtual interface, this
SHOULD result in signaling breakage of that peer to RPL, so it can
trigger RPL DODAG repair, see Section 6.12.1.7.
There is no requirement for all ACP nodes on the same multi-access
subnet to use the same type of ACP virtual interface. This is purely
a node-local decision.
ACP nodes MUST perform standard IPv6 operations across ACP virtual
interfaces including SLAAC [RFC4862] to assign their IPv6 link-local
address on the ACP virtual interface and ND ("Neighbor Discovery for
IP version 6 (IPv6)" [RFC4861]) to discover which IPv6 link-local
neighbor address belongs to which ACP secure channel mapped to the
ACP virtual interface. This is independent of whether the ACP
virtual interface is point-to-point or multi-access.
Optimistic Duplicate Address Detection (DAD) according to "Optimistic
Duplicate Address Detection (DAD) for IPv6" [RFC4429] is RECOMMENDED
because the likelihood for duplicates between ACP nodes is highly
improbable as long as the address can be formed from a globally
unique, locally assigned identifier (e.g., EUI-48/EUI-64, see below).
ACP nodes MAY reduce the amount of link-local IPv6 multicast packets
from ND by learning the IPv6 link-local neighbor address to ACP
secure channel mapping from other messages, such as the source
address of IPv6 link-local multicast RPL messages, and therefore
forego the need to send Neighbor Solicitation messages.
The ACP virtual interface IPv6 link-local address can be derived from
any appropriate local mechanism, such as node-local EUI-48 or EUI-64.
It MUST NOT depend on something that is attackable from the data
plane, such as the IPv6 link-local address of the underlying physical
interface, which can be attacked by SLAAC, or parameters of the
secure channel encapsulation header that may not be protected by the
secure channel mechanism.
The link-layer address of an ACP virtual interface is the address
used for the underlying interface across which the secure tunnels are
built, typically Ethernet addresses. Because unicast IPv6 packets
sent to an ACP virtual interface are not sent to a link-layer
destination address but rather to an ACP secure channel, the link-
layer address fields SHOULD be ignored on reception, and instead the
ACP secure channel from which the message was received should be
remembered.
Multi-access ACP virtual interfaces are preferable implementations
when the underlying interface is a (broadcast) multi-access subnet
because they reflect the presence of the underlying multi-access
subnet to the virtual interfaces of the ACP. This makes it, for
example, simpler to build services with topology awareness inside the
ACP VRF in the same way as they could have been built running
natively on the multi-access interfaces.
Consider also the impact of point-to-point vs. multi-access virtual
interfaces on the efficiency of flooding via link-local multicast
messages.
Assume a LAN with three ACP neighbors, Alice, Bob, and Carol.
Alice's ACP GRASP wants to send a link-local GRASP multicast message
to Bob and Carol. If Alice's ACP emulates the LAN as per-peer,
point-to-point virtual interfaces, one to Bob and one to Carol,
Alice's ACP GRASP will send two copies of multicast GRASP messages:
one to Bob and one to Carol. If Alice's ACP emulates a LAN via a
multipoint virtual interface, Alice's ACP GRASP will send one packet
to that interface, and the ACP multipoint virtual interface will
replicate the packet to each secure channel, one to Bob, one to
Carol. The result is the same. The difference happens when Bob and
Carol receive their packets. If they use ACP point-to-point virtual
interfaces, their GRASP instance would forward the packet from Alice
to each other as part of the GRASP flooding procedure. These packets
are unnecessary and would be discarded by GRASP on receipt as
duplicates (by use of the GRASP Session ID). If Bob and Carol's ACP
emulated a multi-access virtual interface, then this would not happen
because GRASP's flooding procedure does not replicate packets back to
the interface from which they were received.
Note that link-local GRASP multicast messages are not sent directly
as IPv6 link-local multicast UDP messages to ACP virtual interfaces,
but instead to ACP GRASP virtual interfaces that are layered on top
of ACP virtual interfaces to add TCP reliability to link-local
multicast GRASP messages. Nevertheless, these ACP GRASP virtual
interfaces perform the same replication of messages and therefore
have the same impact on flooding. See Section 6.9.2 for more
details.
RPL does support operations and correct routing table construction
across non-broadcast multi-access (NBMA) subnets. This is common
when using many radio technologies. When such NBMA subnets are used,
they MUST NOT be represented as ACP multi-access virtual interfaces
because the replication of IPv6 link-local multicast messages will
not reach all NBMA subnet neighbors. As a result, GRASP message
flooding would fail. Instead, each ACP secure channel across such an
interface MUST be represented as an ACP point-to-point virtual
interface. See also Appendix A.9.4.
Care needs to be taken when creating multi-access ACP virtual
interfaces across ACP secure channels between ACP nodes in different
domains or routing subdomains. If, for example, future inter-domain
ACP policies are defined as "peer-to-peer" policies, it is easier to
create ACP point-to-point virtual interfaces for these inter-domain
secure channels.
7. ACP Support on L2 Switches/Ports (Normative)
7.1. Why (Benefits of ACP on L2 Switches)
ANrtr1 ------ ANswitch1 --- ANswitch2 ------- ANrtr2
.../ \ \ ...
ANrtrM ------ \ ------- ANrtrN
ANswitchM ...
Figure 13: Topology with L2 ACP Switches
Consider a large L2 LAN with routers ANrtr1 through ANrtrN connected
via some topology of L2 switches. Examples include large enterprise
campus networks with an L2 core, IoT networks, or broadband
aggregation networks, which often have a multilevel L2-switched
topology.
If the discovery protocol used for the ACP operates at the subnet
level, every ACP router will see all other ACP routers on the LAN as
neighbors, and a full mesh of ACP channels will be built. If some or
all of the AN switches are autonomic with the same discovery
protocol, then the full mesh would include those switches as well.
A full mesh of ACP connections can create fundamental scale
challenges. The number of security associations of the secure
channel protocols will likely not scale arbitrarily, especially when
they leverage platform-accelerated encryption/decryption. Likewise,
any other ACP operations (such as routing) need to scale to the
number of direct ACP neighbors. An ACP router with just four
physical interfaces might be deployed into a LAN with hundreds of
neighbors connected via switches. Introducing such a new,
unpredictable scaling factor requirement makes it harder to support
the ACP on arbitrary platforms and in arbitrary deployments.
Predictable scaling requirements for ACP neighbors can most easily be
achieved if, in topologies such as these, ACP-capable L2 switches can
ensure that discovery messages terminate on them so that neighboring
ACP routers and switches will only find the physically connected ACP
L2 switches as their candidate ACP neighbors. With such a discovery
mechanism in place, the ACP and its security associations will only
need to scale to the number of physical interfaces instead of a
potentially much larger number of "LAN-connected" neighbors, and the
ACP topology will follow directly the physical topology, something
that can then also be leveraged in management operations or by ASAs.
In the example above, consider that ANswitch1 and ANswitchM are ACP
capable, and ANswitch2 is not ACP capable. The desired ACP topology
is that ANrtr1 and ANrtrM only have an ACP connection to ANswitch1,
and that ANswitch1, ANrtr2, and ANrtrN have a full mesh of ACP
connections amongst each other. ANswitch1 also has an ACP connection
with ANswitchM, and ANswitchM has ACP connections to anything else
behind it.
7.2. How (per L2 Port DULL GRASP)
To support ACP on L2 switches or L2-switched ports of an L3 device,
it is necessary to make those L2 ports look like L3 interfaces for
the ACP implementation. This primarily involves the creation of a
separate DULL GRASP instance/domain on every such L2 port. Because
GRASP has a dedicated link-local IPv6 multicast address
(ALL_GRASP_NEIGHBORS), it is sufficient that all packets for this
address are extracted at the port level and passed to that DULL GRASP
instance. Likewise, the IPv6 link-local multicast packets sent by
that DULL GRASP instance need to be sent only towards the L2 port for
this DULL GRASP instance (instead of being flooded across all ports
of the VLAN to which the port belongs).
When the ports/interfaces across which the ACP is expected to operate
in an ACP-aware L2 switch or L2/L3 switch/router are L2-bridged,
packets for the ALL_GRASP_NEIGHBORS multicast address MUST never be
forwarded between these ports. If MLD snooping is used, it MUST be
prohibited from bridging packets for the ALL_GRASP_NEIGHBORS IPv6
multicast address.
On hybrid L2/L3 switches, multiple L2 ports are assigned to a single
L3 VLAN interface. With the aforementioned changes for DULL GRASP,
ACP can simply operate on the L3 VLAN interfaces, so no further
(hardware) forwarding changes are required to make ACP operate on L2
ports. This is possible because the ACP secure channel protocols
only use link-local IPv6 unicast packets, and these packets will be
sent to the correct L2 port towards the peer by the VLAN logic of the
device.
This is sufficient when P2P ACP virtual interfaces are established to
every ACP peer. When it is desired to create multi-access ACP
virtual interfaces (see Section 6.13.5.2.2), it is REQUIRED not to
coalesce all the ACP secure channels on the same L3 VLAN interface,
but only all those on the same L2 port.
If VLAN tagging is used, then the logic described above only applies
to untagged GRASP packets. For the purpose of ACP neighbor discovery
via GRASP, no VLAN-tagged packets SHOULD be sent or received. In a
hybrid L2/L3 switch, each VLAN would therefore only create ACP
adjacencies across those ports where the VLAN is carried untagged.
As a result, the simple logic is that ACP secure channels would
operate over the same L3 interfaces that present a single, flat
bridged network across all routers, but because DULL GRASP is
separated on a per-port basis, no full mesh of ACP secure channels is
created, but only per-port ACP secure channels to per-port
L2-adjacent ACP node neighbors.
For example, in the above picture, ANswitch1 would run separate DULL
GRASP instances on its ports to ANrtr1, ANswitch2, and ANswitchI,
even though all three ports may be in the data plane in the same
(V)LAN and perform L2 switching between these ports, ANswitch1 would
perform ACP L3 routing between them.
The description in the previous paragraph is specifically meant to
illustrate that, on hybrid L3/L2 devices that are common in
enterprise, IoT, and broadband aggregation, there is only the GRASP
packet extraction (by Ethernet address) and GRASP link-local
multicast per L2-port packet injection that has to consider L2 ports
at the hardware-forwarding level. The remaining operations are
purely ACP control plane and setup of secure channels across the L3
interface. This hopefully makes support for per-L2 port ACP on those
hybrid devices easy.
In devices without such a mix of L2 port/interfaces and L3 interfaces
(to terminate any transport-layer connections), implementation
details will differ. Logically and most simply every L2 port is
considered and used as a separate L3 subnet for all ACP operations.
The fact that the ACP only requires IPv6 link-local unicast and
multicast should make support for it on any type of L2 devices as
simple as possible.
A generic issue with ACP in L2-switched networks is the interaction
with the Spanning Tree Protocol (STP). Without further L2
enhancements, the ACP would run only across the active STP topology,
and the ACP would be interrupted and reconverge with STP changes.
Ideally, ACP peering SHOULD be built also across ports that are
blocked in STP so that the ACP does not depend on STP and can
continue to run unaffected across STP topology changes, where
reconvergence can be quite slow. The above described simple
implementation options are not sufficient to achieve this.
8. Support for Non-ACP Components (Normative)
8.1. ACP Connect
8.1.1. Non-ACP Controller and/or Network Management System (NMS)
The ACP can be used by management systems, such as controllers or NMS
hosts, to connect to devices (or other type of nodes) through it.
For this, an NMS host needs to have access to the ACP. The ACP is a
self-protecting overlay network, which allows access only to trusted,
autonomic systems by default. Therefore, a traditional, non-ACP NMS
does not have access to the ACP by default, such as any other
external node.
If the NMS host is not autonomic, i.e., it does not support autonomic
negotiation of the ACP, then it can be brought into the ACP by
explicit configuration. To support connections to adjacent non-ACP
nodes, an ACP node SHOULD support "ACP connect" (sometimes also
called "autonomic connect").
"ACP connect" is an interface-level, configured workaround for
connection of trusted non-ACP nodes to the ACP. The ACP node on
which ACP connect is configured is called an "ACP edge node". With
ACP connect, the ACP is accessible from those non-ACP nodes (such as
NOC systems) on such an interface without those non-ACP nodes having
to support any ACP discovery or ACP channel setup. This is also
called "native" access to the ACP because, to those NOC systems, the
interface looks like a normal network interface without any ACP
secure channel that is encapsulating the traffic.
Data Plane "native" (no ACP)
.
+--------+ +----------------+ . +-------------+
| ACP | |ACP Edge Node | . | |
| Node | | | v | |
| |-------|...[ACP VRF]....+----------------| |+
| | ^ |. | | NOC Device ||
| | . | .[Data Plane]..+----------------| "NMS hosts" ||
| | . | [ ] | . ^ | ||
+--------+ . +----------------+ . . +-------------+|
. . . +-------------+
. . .
Data Plane "native" . ACP "native" (unencrypted)
+ ACP auto-negotiated . "ACP connect subnet"
and encrypted .
ACP connect interface
e.g., "VRF ACP native" (config)
Figure 14: ACP Connect
ACP connect has security consequences: all systems and processes
connected via ACP connect have access to all ACP nodes on the entire
ACP, without further authentication. Thus, the ACP connect interface
and the NOC systems connected to it need to be physically controlled
and/or secured. For this reason, the mechanisms described here
explicitly do not include options to allow for a non-ACP router to be
connected across an ACP connect interface and addresses behind such a
router routed inside the ACP.
Physically controlled and/or secured means that attackers cannot gain
access to the physical device hosting the ACP edge node, the physical
interfaces and links providing the ACP connect link, nor the physical
devices hosting the NOC device. In a simple case, ACP edge node and
NOC device are colocated in an access-controlled room, such as a NOC,
to which attackers cannot gain physical access.
An ACP connect interface provides exclusive access to only the ACP.
This is likely insufficient for many NMS hosts. Instead, they would
require a second "data plane" interface outside the ACP for
connections between the NMS host and administrators, or Internet-
based services, or for direct access to the data plane. The document
"Using Autonomic Control Plane for Stable Connectivity of Network
OAM" [RFC8368] explains in more detail how the ACP can be integrated
in a mixed NOC environment.
An ACP connect interface SHOULD use an IPv6 address/prefix from the
Manual Addressing Sub-Scheme (Section 6.11.4), letting the operator
configure, for example, only the Subnet-ID and having the node
automatically assign the remaining part of the prefix/address. It
SHOULD NOT use a prefix that is also routed outside the ACP so that
the addresses clearly indicate whether it is used inside the ACP or
not.
The prefix of ACP connect subnets MUST be distributed by the ACP edge
node into the ACP routing protocol, RPL. The NMS host MUST connect
to prefixes in the ACP routing table via its ACP connect interface.
In the simple case where the ACP uses only one ULA prefix, and all
ACP connect subnets have prefixes covered by that ULA prefix, NMS
hosts can rely on [RFC6724] to determine longest match prefix routes
towards its different interfaces, ACP and data plane. With
[RFC6724], the NMS host will select the ACP connect interface for all
addresses in the ACP because any ACP destination address is longest
matched by the address on the ACP connect interface. If the NMS
host's ACP connect interface uses another prefix, or if the ACP uses
multiple ULA prefixes, then the NMS host requires (static) routes
towards the ACP interface for these prefixes.
When an ACP edge node receives a packet from an ACP connect
interface, the ACP edge node MUST only forward the packet to the ACP
if the packet has an IPv6 source address from that interface (this is
sometimes called Reverse Path Forwarding (RPF) filtering). This
filtering rule MAY be changed through administrative measures. The
more any such administrative action enables reachability of non-ACP
nodes to the ACP, the more this may cause security issues.
To limit the security impact of ACP connect, nodes supporting it
SHOULD implement a security mechanism to allow configuration and/or
use of ACP connect interfaces only on nodes explicitly targeted to be
deployed with it (those in physically secure locations such as a
NOC). For example, the registrar could disable the ability to enable
ACP connect on devices during enrollment, and that property could
only be changed through reenrollment. See also Appendix A.9.5.
ACP edge nodes SHOULD have a configurable option to prohibit packets
with RPI headers (see Section 6.12.1.13) across an ACP connect
interface. These headers are outside the scope of the RPL profile in
this specification but may be used in future extensions of this
specification.
8.1.2. Software Components
The previous section assumed that the ACP edge node and NOC devices
are separate physical devices and that the ACP connect interface is a
physical network connection. This section discusses the implication
when these components are instead software components running on a
single physical device.
The ACP connect mechanism can be used not only to connect physically
external systems (NMS hosts) to the ACP but also other applications,
containers, or virtual machines. In fact, one possible way to
eliminate the security issue of the external ACP connect interface is
to colocate an ACP edge node and an NMS host by making one a virtual
machine or container inside the other; therefore converting the
unprotected external ACP subnet into an internal virtual subnet in a
single device. This would ultimately result in a fully ACP-enabled
NMS host with minimum impact to the NMS host's software architecture.
This approach is not limited to NMS hosts but could equally be
applied to devices consisting of one or more VNF (virtual network
functions): an internal virtual subnet connecting out-of-band
management interfaces of the VNFs to an ACP edge router VNF.
The core requirement is that the software components need to have a
network stack that permits access to the ACP and optionally also to
the data plane. Like in the physical setup for NMS hosts, this can
be realized via two internal virtual subnets: one that connects to
the ACP (which could be a container or virtual machine by itself),
and one (or more) connecting to the data plane.
This "internal" use of the ACP connect approach should not be
considered to be a "workaround" because, in this case, it is possible
to build a correct security model: it is not necessary to rely on
unprovable, external physical security mechanisms as in the case of
external NMS hosts. Instead, the orchestration of the ACP, the
virtual subnets, and the software components can be done by trusted
software that could be considered to be part of the ANI (or even an
extended ACP). This software component is responsible for ensuring
that only trusted software components will get access to that virtual
subnet and that only even more trusted software components will get
access to both the ACP virtual subnet and the data plane (because
those ACP users could leak traffic between ACP and data plane). This
trust could be established, for example, through cryptographic means
such as signed software packages.
8.1.3. Autoconfiguration
ACP edge nodes, NMS hosts, and software components that, as described
in the previous section, are meant to be composed via virtual
interfaces SHOULD support SLAAC [RFC4862] on the ACP connect subnet
and route autoconfiguration according to "Default Router Preferences
and More-Specific Routes" [RFC4191].
The ACP edge node acts as the router towards the ACP on the ACP
connect subnet, providing the (auto)configured prefix for the ACP
connect subnet and (auto)configured routes to the ACP to NMS hosts
and/or software components.
The ACP edge node uses the Route Information Option (RIO) of
[RFC4191] to announce aggregated prefixes for address prefixes used
in the ACP (with normal RIO lifetimes). In addition, the ACP edge
node also uses a RIO to announce the default route (::/0) with a
lifetime of 0.
These RIOs allow the connecting of type C hosts to the ACP via an ACP
connect subnet on one interface and another network (Data Plane and/
or NMS network) on the same or another interface of the type C host,
relying on routers other than the ACP edge node. The RIOs ensure
that these hosts will only route the prefixes used in the ACP to the
ACP edge node.
Type A and B hosts ignore the RIOs and will consider the ACP node to
be their default router for all destinations. This is sufficient
when the type A or type B host only needs to connect to the ACP but
not to other networks. Attaching a type A or type B host to both the
ACP and other networks requires explicit ACP prefix route
configuration on either the host or the combined ACP and data plane
interface on the ACP edge node, see Section 8.1.4.
Aggregated prefix means that the ACP edge node needs to only announce
the /48 ULA prefixes used in the ACP but none of the actual /64
(Manual Addressing Sub-Scheme), /127 (Zone Addressing Sub-Scheme),
/112 or /120 (Vlong Addressing Sub-Scheme) routes of actual ACP
nodes. If ACP interfaces are configured with non-ULA prefixes, then
those prefixes cannot be aggregated without further configured policy
on the ACP edge node. This explains the above recommendation to use
ACP ULA prefixes for ACP connect interfaces: they allow for a shorter
list of prefixes to be signaled via [RFC4191] to NMS hosts and
software components.
The ACP edge nodes that have a Vlong ACP address MAY allocate a
subset of their /112 or /120 address prefix to ACP connect
interface(s) to eliminate the need to non-autonomically configure
and/or provision the address prefixes for such ACP connect
interfaces.
8.1.4. Combined ACP and Data Plane Interface (VRF Select)
Combined ACP and data plane interface
.
+--------+ +--------------------+ . +--------------+
| ACP | |ACP Edge No | . | NMS Host(s) |
| Node | | | . | / Software |
| | | [ACP ]. | . | |+
| | | .[VRF ] .[VRF ] | v | "ACP Address"||
| +-------+. .[Select].+--------+ "Data Plane ||
| | ^ | .[Data ]. | | Address(es)"||
| | . | [Plane] | | ||
| | . | [ ] | +--------------+|
+--------+ . +--------------------+ +--------------+
.
Data plane "native" and + ACP auto-negotiated/encrypted
Figure 15: VRF Select
Using two physical and/or virtual subnets (and therefore interfaces)
to NMS hosts (as per Section 8.1.1) or software (as per
Section 8.1.2) may be seen as additional complexity, for example,
with legacy NMS hosts that support only one IP interface, or it may
be insufficient to support type A or type B hosts [RFC4191] (see
Section 8.1.3).
To provide a single subnet to both the ACP and Data plane, the ACP
edge node needs to demultiplex packets from NMS hosts into ACP VRF
and data plane. This is sometimes called "VRF select". If the ACP
VRF has no overlapping IPv6 addresses with the data plane (it should
have no overlapping addresses), then this function can use the IPv6
destination address. The problem is source address selection on the
NMS host(s) according to [RFC6724].
Consider the simple case: the ACP uses only one ULA prefix, and the
ACP IPv6 prefix for the combined ACP and data plane interface is
covered by that ULA prefix. The ACP edge node announces both the ACP
IPv6 prefix and one (or more) prefixes for the data plane. Without
further policy configurations on the NMS host(s), it may select its
ACP address as a source address for data plane ULA destinations
because of Rule 8 (Section 5 of [RFC6724]). The ACP edge node can
pass on the packet to the data plane, but the ACP source address
should not be used for data plane traffic, and return traffic may
fail.
If the ACP carries multiple ULA prefixes or non-ULA ACP connect
prefixes, then the correct source address selection becomes even more
problematic.
With separate ACP connect and data plane subnets and prefix
announcements [RFC4191] that are to be routed across the ACP connect
interface, the source address selection of Rule 5 (use address of
outgoing interface) (Section 5 of [RFC6724]) will be used, so that
above problems do not occur, even in more complex cases of multiple
ULA and non-ULA prefixes in the ACP routing table.
To achieve the same behavior with a combined ACP and data plane
interface, the ACP edge node needs to behave as two separate routers
on the interface: one link-local IPv6 address/router for its ACP
reachability, and one link-local IPv6 address/router for its data
plane reachability. The Router Advertisements for both are as
described in Section 8.1.3: for the ACP, the ACP prefix is announced
together with the prefix option [RFC4191] routed across the ACP, and
the lifetime is set to zero to disqualify this next hop as a default
router. For the data plane, the data plane prefix(es) are announced
together with whatever default router parameters are used for the
data plane.
As a result, source address selection Rule 5.5 (Section 5 of
[RFC6724]) may result in the same correct source address selection
behavior of NMS hosts without further configuration as the separate
ACP connect and data plane interfaces on the host. As described in
the text for Rule 5.5 (Section 5 of [RFC6724]), this is only a MAY
because IPv6 hosts are not required to track next-hop information.
If an NMS host does not do this, then separate ACP connect and data
plane interfaces are the preferable method of attachment. Hosts
implementing "First-Hop Router Selection by Hosts in a Multi-Prefix
Network" [RFC8028] should (instead of may) implement Rule 5.5
(Section 5 of [RFC6724]), so it is preferred for hosts to support
[RFC8028].
ACP edge nodes MAY support the combined ACP and data plane interface.
8.1.5. Use of GRASP
GRASP can and should be possible to use across ACP connect
interfaces, especially in the architecturally correct solution when
it is used as a mechanism to connect software (e.g., ASA or legacy
NMS applications) to the ACP.
Given how the ACP is the security and transport substrate for GRASP,
the requirements are that those devices connected via ACP connect are
equivalently (if not better) secured against attacks than ACP nodes
that do not use ACP connect, and they run only software that is
equally (if not better) protected, known (or trusted) not to be
malicious, and accordingly designed to isolate access to the ACP
against external equipment.
The difference in security is that cryptographic security of the ACP
secure channel is replaced by required physical security and/or
control of the network connection between an ACP edge node and the
NMS or other host reachable via the ACP connect interface. See
Section 8.1.1.
When using the combined ACP and data plane interface, care has to be
taken that only GRASP messages received from software or NMS hosts
and intended for the ACP GRASP domain are forwarded by ACP edge
nodes. Currently there is no definition for a GRASP security and
transport substrate beside the ACP, so there is no definition how
such software/NMS host could participate in two separate GRASP
domains across the same subnet (ACP and data plane domains).
Currently it is assumed that all GRASP packets on a combined ACP and
data plane interface belong to the GRASP ACP domain. They SHOULD all
use the ACP IPv6 addresses of the software/NMS hosts. The link-local
IPv6 addresses of software/NMS hosts (used for GRASP M_DISCOVERY and
M_FLOOD messages) are also assumed to belong to the ACP address
space.
8.2. Connecting ACP Islands over Non-ACP L3 Networks (Remote ACP
Neighbors)
Not all nodes in a network may support the ACP. If non-ACP L2
devices are between ACP nodes, the ACP will work across them since it
is IP based. However, the autonomic discovery of ACP neighbors via
DULL GRASP is only intended to work across L2 connections, so it is
not sufficient to autonomically create ACP connections across non-ACP
L3 devices.
8.2.1. Configured Remote ACP Neighbor
On the ACP node, remote ACP neighbors are configured explicitly. The
parameters of such a "connection" are described in the following
ABNF. The syntax shown is non-normative (as there are no standards
for configuration) but only meant to illustrate the parameters and
which ones can be optional.
connection = method "," local-addr "," remote-addr [ "," pmtu ]
method = "any"
/ ( "IKEv2" [ ":" port ] )
/ ( "DTLS" [ ":" port ] )
port = 1*DIGIT
local-addr = [ address [ ":" vrf ] ]
remote-addr = address
address = "any"
/ IPv4address / IPv6address ; From [RFC5954]
vrf = system-dependent ; Name of VRF for local-address
Figure 16: Parameters for Remote ACP Neighbors
Explicit configuration of a remote peer according to this ABNF
provides all the information to build a secure channel without
requiring a tunnel to that peer and running DULL GRASP inside of it.
The configuration includes the parameters otherwise signaled via DULL
GRASP: local address, remote (peer) locator, and method. The
differences over DULL GRASP local neighbor discovery and secure
channel creation are as follows:
* The local and remote address can be IPv4 or IPv6 and are typically
global-scope addresses.
* The VRF across which the connection is built (and in which local-
addr exists) can be specified. If vrf is not specified, it is the
default VRF on the node. In DULL GRASP, the VRF is implied by the
interface across which DULL GRASP operates.
* If local address is "any", the local address used when initiating
a secure channel connection is decided by source address selection
([RFC6724] for IPv6). As a responder, the connection listens on
all addresses of the node in the selected VRF.
* Configuration of port is only required for methods where no
defaults exist (e.g., "DTLS").
* If the remote address is "any", the connection is only a
responder. It is a "hub" that can be used by multiple remote
peers to connect simultaneously -- without having to know or
configure their addresses, for example, a hub site for remote
"spoke" sites reachable over the Internet.
* The pmtu parameter should be configurable to overcome issues or
limitations of Path MTU Discovery (PMTUD).
* IKEv2/IPsec to remote peers should support the optional NAT
Traversal (NAT-T) procedures.
8.2.2. Tunneled Remote ACP Neighbor
An IP-in-IP, GRE, or other form of preexisting tunnel is configured
between two remote ACP peers, and the virtual interfaces representing
the tunnel are configured for "ACP enable". This will enable IPv6
link-local addresses and DULL on this tunnel. As a result, the
tunnel is used for normal "L2 adjacent" candidate ACP neighbor
discovery with DULL and secure channel setup procedures described in
this document.
Tunneled Remote ACP Neighbor requires two encapsulations: the
configured tunnel and the secure channel inside of that tunnel. This
makes it in general less desirable than Configured Remote ACP
Neighbor. Benefits of tunnels are that it may be easier to implement
because there is no change to the ACP functionality - just running it
over a virtual (tunnel) interface instead of only native interfaces.
The tunnel itself may also provide PMTUD while the secure channel
method may not. Or the tunnel mechanism is permitted/possible
through some firewall while the secure channel method may not.
Tunneling using an insecure tunnel encapsulation increases, on
average, the risk of a MITM downgrade attack somewhere along the
underlay path. In such an attack, the MITM filters packets for all
but the most easily attacked ACP secure channel option to force use
of that option. ACP nodes supporting Tunneled Remote ACP Neighbors
SHOULD support configuration on such tunnel interfaces to restrict or
explicitly select the available ACP secure channel protocols (if the
ACP node supports more than one ACP secure channel protocol in the
first place).
8.2.3. Summary
Configured and Tunneled Remote ACP Neighbors are less
"indestructible" than L2 adjacent ACP neighbors based on link-local
addressing, since they depend on more correct data plane operations,
such as routing and global addressing.
Nevertheless, these options may be crucial to incrementally deploying
the ACP, especially if it is meant to connect islands across the
Internet. Implementations SHOULD support at least Tunneled Remote
ACP Neighbors via GRE tunnels, which is likely the most common
router-to-router tunneling protocol in use today.
9. ACP Operations (Informative)
The following sections document important operational aspects of the
ACP. They are not normative because they do not impact the
interoperability between components of the ACP, but they include
recommendations and/or requirements for the internal operational
model that are beneficial or necessary to achieve the desired use-
case benefits of the ACP (see Section 3).
* Section 9.1 describes the recommended capabilities of operator
diagnostics of ACP nodes.
* Section 9.2 describes at a high level how an ACP registrar needs
to work, what its configuration parameters are, and specific
issues impacting the choices of deployment design due to renewal
and revocation issues. It describes a model where ACP registrars
have their own sub-CA to provide the most distributed deployment
option for ACP registrars, and it describes considerations for
centralized policy control of ACP registrar operations.
* Section 9.3 describes suggested ACP node behavior and operational
interfaces (configuration options) to manage the ACP in so-called
greenfield devices (previously unconfigured) and brownfield
devices (preconfigured).
The recommendations and suggestions of this chapter were derived from
operational experience gained with a commercially available pre-
standard ACP implementation.
9.1. ACP (and BRSKI) Diagnostics
Even though ACP and ANI in general are removing many manual
configuration mistakes through their automation, it is important to
provide good diagnostics for them.
Basic standardized diagnostics would require support for (YANG)
models representing the complete (auto)configuration and operational
state of all components: GRASP, ACP, and the infrastructure used by
them, such as TLS/DTLS, IPsec, certificates, TA, time, VRF, and so
on. While necessary, this is not sufficient.
Simply representing the state of components does not allow operators
to quickly take action -- unless they understand how to interpret the
data, which can mean a requirement for deep understanding of all
components and how they interact in the ACP/ANI.
Diagnostic supports should help to quickly answer the questions
operators are expected to ask, such as "Is the ACP working
correctly?" or "Why is there no ACP connection to a known neighboring
node?"
In current network management approaches, the logic to answer these
questions is most often built into centralized diagnostics software
that leverages the above mentioned data models. While this approach
is feasible for components utilizing the ANI, it is not sufficient to
diagnose the ANI itself:
* Developing the logic to identify common issues requires
operational experience with the components of the ANI. Letting
each management system define its own analysis is inefficient.
* When the ANI is not operating correctly, it may not be possible to
run diagnostics remotely because of missing connectivity. The ANI
should therefore have diagnostic capabilities available locally on
the nodes themselves.
* Certain operations are difficult or impossible to monitor in real
time, such as initial bootstrap issues in a network location where
no capabilities exist to attach local diagnostics. Therefore, it
is important to also define how to capture (log) diagnostics
locally for later retrieval. Ideally, these captures are also
nonvolatile so that they can survive extended power-off
conditions, for example, when a device that fails to be brought up
zero-touch is sent for diagnostics at a more appropriate location.
The simplest form of diagnostics for answering questions such as the
above is to represent the relevant information sequentially in
dependency order, so that the first unexpected and/or nonoperational
item is the most likely root cause, or just log and/or highlight that
item. For example:
Question: Is the ACP operational to accept neighbor connections?
* Check if the necessary configurations to make ACP/ANI operational
are correct (see Section 9.3 for a discussion of such commands).
* Does the system time look reasonable, or could it be the default
system time after battery failure of the clock chip? Certificate
checks depend on reasonable notion of time.
* Does the node have keying material, such as domain certificate, TA
certificates, etc.?
* If there is no keying material and the ANI is supported/enabled,
check the state of BRSKI (not detailed in this example).
* Check the validity of the domain certificate:
- Does the certificate validate against the TA?
- Has it been revoked?
- Was the last scheduled attempt to retrieve a CRL successful?
(e.g., do we know that our CRL information is up to date?)
- Is the certificate valid? The validity start time is in the
past, and the expiration time is in the future?
- Does the certificate have a correctly formatted acp-node-name
field?
* Was the ACP VRF successfully created?
* Is ACP enabled on one or more interfaces that are up and running?
If all of the above looks good, the ACP should be running "fine"
locally, but we did not check any ACP neighbor relationships.
Question: Why does the node not create a working ACP connection to a
neighbor on an interface?
* Is the interface physically up? Does it have an IPv6 link-local
address?
* Is it enabled for ACP?
* Do we successfully send DULL GRASP messages to the interface?
(Are there link-layer errors?)
* Do we receive DULL GRASP messages on the interface? If not, some
intervening L2 equipment performing bad MLD snooping could have
caused problems. Provide, e.g., diagnostics of the MLD querier
IPv6 and MAC address.
* Do we see the ACP objective in any DULL GRASP message from that
interface? Diagnose the supported secure channel methods.
* Do we know the MAC address of the neighbor with the ACP objective?
If not, diagnose SLAAC/ND state.
* When did we last attempt to build an ACP secure channel to the
neighbor?
* If it failed:
- Did the neighbor close the connection on us, or did we close
the connection on it because the domain certificate membership
failed?
- If the neighbor closed the connection on us, provide any error
diagnostics from the secure channel protocol.
- If we failed the attempt, display our local reason:
o There was no common secure channel protocol supported by the
two neighbors (this could not happen on nodes supporting
this specification because it mandates common support for
IPsec).
o Did the ACP certificate membership check (Section 6.2.3)
fail?
+ The neighbor's certificate is not signed directly or
indirectly by one of the node's TA. Provide diagnostics
which TA it has (can identify whom the device belongs
to).
+ The neighbor's certificate does not have the same domain
(or no domain at all). Diagnose acp-domain-name and
potentially other cert info.
+ The neighbor's certificate has been revoked or could not
be authenticated by OCSP.
+ The neighbor's certificate has expired, or it is not yet
valid.
- Are there any other connection issues, e.g., IKEv2/IPsec, DTLS?
Question: Is the ACP operating correctly across its secure channels?
* Are there one or more active ACP neighbors with secure channels?
* Is RPL for the ACP running?
* Is there a default route to the root in the ACP routing table?
* Is there, for each direct ACP neighbor not reachable over the ACP
virtual interface to the root, a route in the ACP routing table?
* Is ACP GRASP running?
* Is at least one "SRV.est" objective cached (to support certificate
renewal)?
* Is there at least one BRSKI registrar objective cached? (If BRSKI
is supported.)
* Is the BRSKI proxy operating normally on all interfaces where ACP
is operating?
These lists are not necessarily complete, but they illustrate the
principle and show that there are variety of issues ranging from
normal operational causes (a neighbor in another ACP domain) to
problems in the credentials management (certificate lifetimes), to
explicit security actions (revocation) or unexpected connectivity
issues (intervening L2 equipment).
The items so far illustrate how the ANI operations can be diagnosed
with passive observation of the operational state of its components
including historic, cached, and/or counted events. This is not
necessarily sufficient to provide good enough diagnostics overall.
The components of ACP and BRSKI are designed with security in mind,
but they do not attempt to provide diagnostics for building the
network itself. Consider two examples:
1. BRSKI does not allow for a neighboring device to identify the
pledge's IDevID certificate. Only the selected BRSKI registrar
can do this, but it may be difficult to disseminate information
from those BRSKI registrars about undesired pledges to locations
and/or nodes where information about those pledges is desired.
2. LLDP disseminates information about nodes, such as node model,
type, and/or software and interface name and/or number of the
connection, to their immediate neighbors. This information is
often helpful or even necessary in network diagnostics. It can
equally be considered too insecure to make this information
available unprotected to all possible neighbors.
An "interested adjacent party" can always determine the IDevID
certificate of a BRSKI pledge by behaving like a BRSKI proxy/
registrar. Therefore, the IDevID certificate of a BRSKI pledge is
not meant to be protected -- it just has to be queried and is not
signaled unsolicited (as it would be in LLDP) so that other observers
on the same subnet can determine who is an "interested adjacent
party".
9.1.1. Secure Channel Peer Diagnostics
When using mutual certificate authentication, the TA certificate is
not required to be signaled explicitly because its hash is sufficient
for certificate chain validation. In the case of ACP secure channel
setup, this leads to limited diagnostics when authentication fails
because of TA mismatch. For this reason, Section 6.8.2 recommends
also including the TA certificate in the secure channel signaling.
This should be possible to do without modifying the security
association protocols used by the ACP. For example, while [RFC7296]
does not mention this, it also does not prohibit it.
One common use case where diagnostics through the signaled TA of a
candidate peer are very helpful is the multi-tenant environment, such
as an office building, where different tenants run their own networks
and ACPs. Each tenant is given supposedly disjoint L2 connectivity
through the building infrastructure. In these environments, there
are various common errors through which a device may receive L2
connectivity into the wrong tenant's network.
While the ACP itself is not impacted by this, the data plane to be
built later may be impacted. Therefore, it is important to be able
to diagnose such undesirable connectivity from the ACP so that any
autonomic or non-autonomic mechanisms to configure the data plane can
treat such interfaces accordingly. The information in the TA of the
peer can then ease troubleshooting of such issues.
Another use case is the intended or accidental reactivation of
equipment, such as redundant gear taken from storage, whose TA
certificate has long expired.
A third use case is when, in a merger and acquisition case, ACP nodes
have not been correctly provisioned with the mutual TA of a
previously disjoint ACP. This assumes that the ACP domain names were
already aligned so that the ACP domain membership check is only
failing on the TA.
A fourth use case is when multiple registrars are set up for the same
ACP but are not correctly set up with the same TA. For example, when
registrars support also being CAs themselves but are misconfigured to
become TAs instead of intermediate CAs.
9.2. ACP Registrars
As described in Section 6.11.7, the ACP addressing mechanism is
designed to enable lightweight, distributed, and uncoordinated ACP
registrars that provide ACP address prefixes to candidate ACP nodes
by enrolling them with an ACP certificate into an ACP domain via any
appropriate mechanism and/or protocol, automated or not.
This section discusses informatively more details and options for ACP
registrars.
9.2.1. Registrar Interactions
This section summarizes and discusses the interactions with other
entities required by an ACP registrar.
In a simple instance of an ACP network, no central NOC component
beside a TA is required. Typically, this is a root CA. One or more
uncoordinated acting ACP registrars can be set up, performing the
following interactions.
To orchestrate enrolling a candidate ACP node autonomically, the ACP
registrar can rely on the ACP and use proxies to reach the candidate
ACP node, therefore allowing minimal, preexisting (auto)configured
network services on the candidate ACP node. BRSKI defines the BRSKI
proxy, a design that can be adopted for various protocols that
pledges and/or candidate ACP nodes could want to use, for example,
BRSKI over CoAP (Constrained Application Protocol) or the proxying of
NETCONF.
To reach a TA that has no ACP connectivity, the ACP registrar uses
the data plane. The ACP and data plane in an ACP registrar could
(and by default should) be completely isolated from each other at the
network level. Only applications such as the ACP registrar would
need the ability for their transport stacks to access both.
In non-autonomic enrollment options, the data plane between an ACP
registrar and the candidate ACP node needs to be configured first.
This includes the ACP registrar and the candidate ACP node. Then any
appropriate set of protocols can be used between the ACP registrar
and the candidate ACP node to discover the other side, and then
connect and enroll (configure) the candidate ACP node with an ACP
certificate. For example, NETCONF Zero Touch ("Secure Zero Touch
Provisioning (SZTP)" [RFC8572]) is a protocol that could be used for
this. BRSKI using optional discovery mechanisms is equally a
possibility for candidate ACP nodes attempting to be enrolled across
non-ACP networks, such as the Internet.
When a candidate ACP node, such as a BRSKI pledge, has secure
bootstrap, it will not trust being configured and/or enrolled across
the network unless it is presented with a voucher (see "A Voucher
Artifact for Bootstrapping Protocols" [RFC8366]) authorizing the
network to take possession of the node. An ACP registrar will then
need a method to retrieve such a voucher, either offline or online
from a MASA (Manufacturer Authorized Signing Authority). BRSKI and
NETCONF Zero Touch are two protocols that include capabilities to
present the voucher to the candidate ACP node.
An ACP registrar could operate EST for ACP certificate renewal and/or
act as a CRL Distribution Point. A node performing these services
does not need to support performing (initial) enrollment, but it does
require the same above described connectivity as an ACP registrar:
via the ACP to the ACP nodes and via the data plane to the TA and
other sources of CRL information.
9.2.2. Registrar Parameters
The interactions of an ACP registrar outlined in Section 6.11.7 and
Section 9.2.1 depend on the following parameters:
* A URL to the TA and credentials so that the ACP registrar can let
the TA sign candidate ACP node certificates.
* The ACP domain name.
* The Registrar-ID to use. This could default to a MAC address of
the ACP registrar.
* For recovery, the next usable Node-IDs for the Zone Addressing
Sub-Scheme (Zone-ID 0) and for the Vlong Addressing Sub-Scheme
(/112 and /120). These IDs would only need to be provisioned
after recovering from a crash. Some other mechanism would be
required to remember these IDs in a backup location or to recover
them from the set of currently known ACP nodes.
* Policies on whether the candidate ACP nodes should receive a
domain certificate or not, for example, based on the device's
IDevID certificate as in BRSKI. The ACP registrar may whitelist
or blacklist based on a device's "serialNumber" attribute [X.520]
in the subject field distinguished name encoding of its IDevID
certificate.
* Policies on what type of address prefix to assign to a candidate
ACP device, likely based on the same information.
* For BRSKI or other mechanisms using vouchers: parameters to
determine how to retrieve vouchers for specific types of secure
bootstrap candidate ACP nodes (such as MASA URLs), unless this
information is automatically learned, such as from the IDevID
certificate of candidate ACP nodes (as defined in BRSKI).
9.2.3. Certificate Renewal and Limitations
When an ACP node renews and/or rekeys its certificate, it may end up
doing so via a different registrar (e.g., EST server) than the one it
originally received its ACP certificate from, for example, because
that original ACP registrar is gone. The ACP registrar through which
the renewal/rekeying is performed would by default trust the acp-
node-name from the ACP node's current ACP certificate and maintain
this information so that the ACP node maintains its ACP address
prefix. In EST renewal/rekeying, the ACP node's current ACP
certificate is signaled during the TLS handshake.
This simple scenario has two limitations:
1. The ACP registrar cannot directly assign certificates to nodes
and therefore needs an "online" connection to the TA.
2. Recovery from a compromised ACP registrar is difficult. When an
ACP registrar is compromised, it can insert, for example, a
conflicting acp-node-name and thereby create an attack against
other ACP nodes through the ACP routing protocol.
Even when such a malicious ACP registrar is detected, resolving the
problem may be difficult because it would require identifying all the
wrong ACP certificates assigned via the ACP registrar after it was
compromised. Without additional centralized tracking of assigned
certificates, there is no way to do this.
9.2.4. ACP Registrars with Sub-CA
In situations where either of the above two limitations are an issue,
ACP registrars could also be sub-CAs. This removes the need for
connectivity to a TA whenever an ACP node is enrolled, and it reduces
the need for connectivity of such an ACP registrar to a TA to only
those times when it needs to renew its own certificate. The ACP
registrar would also now use its own (sub-CA) certificate to enroll
and sign the ACP node's certificates, and therefore it is only
necessary to revoke a compromised ACP registrar's sub-CA certificate.
Alternatively, one can let it expire and not renew it when the
certificate of the sub-CA is appropriately short-lived.
As the ACP domain membership check verifies a peer ACP node's ACP
certificate trust chain, it will also verify the signing certificate,
which is the compromised and/or revoked sub-CA certificate.
Therefore, ACP domain membership for an ACP node enrolled by a
compromised and discovered ACP registrar will fail.
ACP nodes enrolled by a compromised ACP registrar would automatically
fail to establish ACP channels and ACP domain certificate renewal via
EST and therefore revert to their role as candidate ACP members and
attempt to get a new ACP certificate from an ACP registrar, for
example, via BRSKI. As a result, ACP registrars that have an
associated sub-CA make isolating and resolving issues with
compromised registrars easier.
Note that ACP registrars with sub-CA functionality also can control
the lifetime of ACP certificates more easily and therefore can be
used as a tool to introduce short-lived certificates and to no longer
rely on CRL, whereas the certificates for the sub-CAs themselves
could be longer lived and subject to CRL.
9.2.5. Centralized Policy Control
When using multiple, uncoordinated ACP registrars, several advanced
operations are potentially more complex than with a single, resilient
policy control backend, for example, including but not limited to the
following:
* Deciding which candidate ACP node is permitted or not permitted
into an ACP domain. This may not be a decision to be made
upfront, so that a policy per "serialNumber" attribute in the
subject field distinguished name encoding can be loaded into every
ACP registrar. Instead, it may better be decided in real time,
potentially including a human decision in a NOC.
* Tracking all enrolled ACP nodes and their certificate information.
For example, in support of revoking an individual ACP node's
certificates.
* Needing more flexible policies as to which type of address prefix
or even which specific address prefix to assign to a candidate ACP
node.
These and other operations could be introduced more easily by
introducing a centralized Policy Management System (PMS) and
modifying ACP registrar behavior so that it queries the PMS for any
policy decision occurring during the candidate ACP node enrollment
process and/or the ACP node certificate renewal process, for example,
which ACP address prefix to assign. Likewise, the ACP registrar
would report any relevant state change information to the PMS as
well, for example, when a certificate was successfully enrolled onto
a candidate ACP node.
9.3. Enabling and Disabling the ACP and/or the ANI
Both ACP and BRSKI require interfaces to be operational enough to
support the sending and receiving of their packets. In node types
where interfaces are enabled by default (e.g., without operator
configuration), such as most L2 switches, this would be less of a
change in behavior than in most L3 devices (e.g., routers), where
interfaces are disabled by default. In almost all network devices,
though, it is common for configuration to change interfaces to a
physically disabled state, and this would break the ACP.
In this section, we discuss a suggested operational model to enable
and disable interfaces and nodes for ACP/ANI in a way that minimizes
the risk of breaking the ACP due to operator action and also
minimizes operator surprise when the ACP/ANI becomes supported in
node software.
9.3.1. Filtering for Non-ACP/ANI Packets
Whenever this document refers to enabling an interface for ACP (or
BRSKI), it only requires permitting the interface to send and receive
packets necessary to operate ACP (or BRSKI) -- but not any other data
plane packets. Unless the data plane is explicitly configured and
enabled, all packets that are not required for ACP/BRSKI should be
filtered on input and output.
Both BRSKI and ACP require link-local-only IPv6 operations on
interfaces and DULL GRASP. IPv6 link-local operations mean the
minimum signaling to auto-assign an IPv6 link-local address and talk
to neighbors via their link-local addresses: SLAAC [RFC4862] and ND
[RFC4861]. When the device is a BRSKI pledge, it may also require
TCP/TLS connections to BRSKI proxies on the interface. When the
device has keying material, and the ACP is running, it requires DULL
GRASP packets and packets necessary for the secure channel mechanism
it supports, e.g., IKEv2 and IPsec ESP packets or DTLS packets to the
IPv6 link-local address of an ACP neighbor on the interface. It also
requires TCP/TLS packets for its BRSKI proxy functionality if it
supports BRSKI.
9.3.2. "admin down" State
Interfaces on most network equipment have at least two states: "up"
and "down". These may have product-specific names. For example,
"down" could be called "shutdown", and "up" could be called "no
shutdown". The "down" state disables all interface operations down
to the physical level. The "up" state enables the interface enough
for all possible L2/L3 services to operate on top of it, and it may
also auto-enable some subset of them. More commonly, the operations
of various L2/L3 services are controlled via additional node-wide or
interface-level options, but they all become active only when the
interface is not "down". Therefore, an easy way to ensure that all
L2/L3 operations on an interface are inactive is to put the interface
into "down" state. The fact that this also physically shuts down the
interface is just a side effect in many cases, but it may be
important in other cases (see Section 9.3.2.2).
A common problem of remote management is the operator or SDN
controller cutting its own connectivity to the remote node via
configuration, impacting its own management connection to the node.
The ACP itself should have no dedicated configuration other than the
aforementioned enabling of the ACP on brownfield ACP nodes. This
leaves configuration that cannot distinguish between the ACP and data
plane as sources of configuration mistakes as these commands will
impact the ACP even though they should only impact the data plane.
The one ubiquitous type of command that does this on many types of
routers is the interface "down" command/configuration. When such a
command is applied to the interface through which the ACP provides
access for remote management, it cuts the remote management
connection through the ACP because, as outlined above, the "down"
command typically impacts the physical layer, too, and not only the
data plane services.
To provide ACP/ANI resilience against such operator misconfiguration,
this document recommends separating the "down" state of interfaces
into an "admin down" state, where the physical layer is kept running
and the ACP/ANI can use the interface, and a "physical down" state.
Any existing "down" configurations would map to "admin down". In
"admin down", any existing L2/L3 services of the data plane should
see no difference to "physical down" state. To ensure that no data
plane packets could be sent or received, packet filtering could be
established automatically as described in Section 9.3.1.
An example of ANI, but not ACP, traffic that should be permitted to
pass even in "admin down" state is BRSKI enrollment traffic between a
BRSKI pledge and a BRSKI proxy.
New configuration options could be introduced as necessary (see
discussion below) to issue "physical down". The options should be
provided with additional checks to minimize the risk of issuing them
in a way that breaks the ACP without automatic restoration. Examples
of checks include not allowing the option to be issued from a control
connection (NETCONF/SSH) that goes across the interface itself ("do
not disconnect yourself") or only applying the option after
additional reconfirmation.
The following subsections discuss important aspects of the
introduction of "admin down" state.
9.3.2.1. Security
Interfaces are physically brought down (or left in default "down"
state) as a form of security. The "admin down" state as described
above also provides also a high level of security because it only
permits ACP/ANI operations, which are both well secured. Ultimately,
it is subject to the deployment's security review whether "admin
down" is a feasible replacement for "physical down".
The need to trust the security of ACP/ANI operations needs to be
weighed against the operational benefits of permitting the following:
consider the typical example of a CPE (customer premises equipment)
with no on-site network expert. User ports are in "physical down"
state unless explicitly configured not to be. In a misconfiguration
situation, the uplink connection is incorrectly plugged into such a
user port. The device is disconnected from the network, and
therefore diagnostics from the network side are no longer possible.
Alternatively, all ports default to "admin down". The ACP (but not
the data plane) would still automatically form. Diagnostics from the
network side are possible, and operator reaction could include either
to make this port the operational uplink port or to instruct re-
cabling. Security wise, only the ACP/ANI could be attacked, all
other functions are filtered on interfaces in "admin down" state.
9.3.2.2. Fast State Propagation and Diagnostics
The "physical down" state propagates on many interface types (e.g.,
Ethernet) to the other side. This can trigger fast L2/L3 protocol
reaction on the other side, and "admin down" would not have the same
(fast) result.
Bringing interfaces to "physical down" state is, to the best of our
knowledge, always a result of operator action and, today, never the
result of autonomic L2/L3 services running on the nodes. Therefore,
one option is to end the operator's reliance on interface state
propagation via the subnet link or physical layer. This may not be
possible when both sides are under the control of different
operators, but in that case, it is unlikely that the ACP is running
across the link, and actually putting the interface into "physical
down" state may still be a good option.
Ideally, fast physical state propagation is replaced by fast
software-driven state propagation. For example, a DULL GRASP "admin-
state" objective could be used to autoconfigure a BFD session
("Bidirectional Forwarding Detection (BFD)" [RFC5880]) between the
two sides of the link that would be used to propagate the "up" vs.
"admin down" state.
Triggering "physical down" state may also be used as a means of
diagnosing cabling issues in the absence of easier methods. It is
more complex than automated neighbor diagnostics because it requires
coordinated remote access to (likely) both sides of a link to
determine whether up/down toggling will cause the same reaction on
the remote side.
See Section 9.1 for a discussion about how LLDP and/or diagnostics
via GRASP could be used to provide neighbor diagnostics and therefore
hopefully eliminate the need for "physical down" for neighbor
diagnostics -- as long as both neighbors support ACP/ANI.
9.3.2.3. Low-Level Link Diagnostics
The "physical down" state is used to diagnose low-level interface
behavior when higher-layer services (e.g., IPv6) are not working.
Ethernet links are especially subject to a wide variety of possible
incorrect configurations/cablings if they do not support automatic
selection of variable parameters such as speed (10/100/1000 Mbps),
crossover (automatic medium-dependent interface crossover (MDI-X)),
and connector (fiber, copper -- when interfaces have multiple but can
only enable one at a time). The need for low-level link diagnostics
can therefore be minimized by using fully autoconfiguring links.
In addition to the "physical down" state, low-level diagnostics of
Ethernet or other interfaces also involve the creation of other
states on interfaces, such as physical loopback (internal and/or
external) or the bringing down of all packet transmissions for
reflection and/or cable-length measurements. Any of these options
would disrupt ACP as well.
In cases where such low-level diagnostics of an operational link are
desired but where the link could be a single point of failure for the
ACP, the ASA on both nodes of the link could perform a negotiated
diagnostic that automatically terminates in a predetermined manner
without dependence on external input, ensuring the link will become
operational again.
9.3.2.4. Power Consumption Issues
Power consumption of "physical down" interfaces may be significantly
lower than those in "admin down" state, for example, on long-range
fiber interfaces. Bringing up interfaces, for example, to probe
reachability may also consume additional power. This can make these
types of interfaces inappropriate to operate purely for the ACP when
they are not currently needed for the data plane.
9.3.3. Enabling Interface-Level ACP and ANI
The interface-level configuration option "ACP enable" enables ACP
operations on an interface, starting with ACP neighbor discovery via
DULL GRASP. The interface-level configuration option "ANI enable" on
nodes supporting BRSKI and ACP starts with BRSKI pledge operations
when there is no domain certificate on the node. On ACP/BRSKI nodes,
only "ANI enable" may need to be supported and not "ACP enable".
Unless overridden by global configuration options (see
Section 9.3.4), either "ACP enable" or "ANI enable" (both abbreviated
as "ACP/ANI enable") will result in the "down" state on an interface
behaving as "admin down".
9.3.4. Which Interfaces to Auto-Enable?
Section 6.4 requires that "ACP enable" is automatically set on native
interfaces, but not on non-native interfaces (reminder: a native
interface is one that exists without operator configuration action,
such as physical interfaces in physical devices).
Ideally, "ACP enable" is set automatically on all interfaces that
provide access to additional connectivity, which allows more nodes of
the ACP domain to be reached. The best set of interfaces necessary
to achieve this is not possible to determine automatically. Native
interfaces are the best automatic approximation.
Consider an ACP domain of ACP nodes transitively connected via native
interfaces. A data plane tunnel between two of these nodes that are
nonadjacent is created, and "ACP enable" is set for that tunnel. ACP
RPL sees this tunnel as just as a single hop. Routes in the ACP
would use this hop as an attractive path element to connect regions
adjacent to the tunnel nodes. As a result, the actual hop-by-hop
paths used by traffic in the ACP can become worse. In addition,
correct forwarding in the ACP now depends on correct data plane
forwarding configuration including QoS, filtering, and other security
on the data plane path across which this tunnel runs. This is the
main reason why "ACP/ANI enable" should not be set automatically on
non-native interfaces.
If the tunnel would connect two previously disjoint ACP regions, then
it likely would be useful for the ACP. A data plane tunnel could
also run across nodes without ACP and provide additional connectivity
for an already connected ACP network. The benefit of this additional
ACP redundancy has to be weighed against the problems of relying on
the data plane. If a tunnel connects two separate ACP regions, how
many tunnels should be created to connect these ACP regions reliably
enough? Between which nodes? These are all standard tunneled
network design questions not specific to the ACP, and there are no
generic, fully automated answers.
Instead of automatically setting "ACP enable" on these types of
interfaces, the decision needs to be based on the use purpose of the
non-native interface, and "ACP enable" needs to be set in conjunction
with the mechanism through which the non-native interface is created
and/or configured.
In addition to the explicit setting of "ACP/ANI enable", non-native
interfaces also need to support configuration of the ACP RPL cost of
the link to avoid the problems of attracting too much traffic to the
link as described above.
Even native interfaces may not be able to automatically perform BRSKI
or ACP because they may require additional operator input to become
operational. Examples include DSL interfaces requiring Point-to-
Point Protocol over Ethernet (PPPoE) credentials or mobile interfaces
requiring credentials from a SIM card. Whatever mechanism is used to
provide the necessary configuration to the device to enable the
interface can also be expanded to decide whether or not to set "ACP/
ANI enable".
The goal of automatically setting "ACP/ANI enable" on interfaces
(native or not) is to eliminate unnecessary "touches" to the node to
make its operation as much as possible "zero-touch" with respect to
ACP/ANI. If there are "unavoidable touches" such a creating and/or
configuring a non-native interface or provisioning credentials for a
native interface, then "ACP/ANI enable" should be added as an option
to that "touch". If an erroneous "touch" is easily fixed (does not
create another high-cost touch), then the default should be not to
enable ANI/ACP, and if it is potentially expensive or slow to fix
(e.g., parameters on SIM card shipped to remote location), then the
default should be to enable ACP/ANI.
9.3.5. Enabling Node-Level ACP and ANI
A node-level command "ACP/ANI enable [up-if-only]" enables ACP or ANI
on the node (ANI = ACP + BRSKI). Without this command set, any
interface-level "ACP/ANI enable" is ignored. Once set, ACP/ANI will
operate an interface where "ACP/ANI enable" is set. Setting of
interface-level "ACP/ANI enable" is either automatic (default) or
explicit through operator action as described in Section 9.3.4.
If the option "up-if-only" is selected, the behavior of "down"
interfaces is unchanged, and ACP/ANI will only operate on interfaces
where "ACP/ANI enable" is set and that are "up". When it is not set,
then "down" state of interfaces with "ACP/ANI enable" is modified to
behave as "admin down".
9.3.5.1. Brownfield Nodes
A "brownfield" node is one that already has a configured data plane.
Executing global "ACP/ANI enable [up-if-only]" on each node is the
only command necessary to create an ACP across a network of
brownfield nodes once all the nodes have a domain certificate. When
BRSKI is used ("ANI enable"), provisioning of the certificates only
requires the setup of a single BRSKI registrar node, which could also
implement a CA for the network. This is the simplest way to
introduce ACP/ANI into existing (i.e., brownfield) networks.
The need to explicitly enable ACP/ANI is especially important in
brownfield nodes because otherwise software updates may introduce
support for ACP/ANI. The automatic enabling of ACP/ANI in networks
where the operator does not want ACP/ANI or has likely never even
heard of it could be quite irritating to the operator, especially
when "down" behavior is changed to "admin down".
Automatically setting "ANI enable" on brownfield nodes where the
operator is unaware of BRSKI and MASA operations could also be an
unlikely, but critical, security issue. If an attacker could
impersonate the operator by registering as the operator at the MASA
or otherwise getting hold of vouchers and could get enough physical
access to the network so pledges would register to an attacking
registrar, then the attacker could gain access to the ACP and,
through the ACP, gain access to the data plane.
In networks where the operator explicitly enables the ANI, this could
not happen because the operator would create a BRSKI registrar that
would discover attack attempts, and the operator would set up his
registrar with the MASA. Nodes requiring "ownership vouchers" would
not be subject to that attack. See [RFC8995] for more details. Note
that a global "ACP enable" alone is not subject to these types of
attacks because they always depend on some other mechanism first to
provision domain certificates into the device.
9.3.5.2. Greenfield Nodes
An ACP "greenfield" node is one that does not have any prior
configuration and that can be bootstrapped into the ACP across the
network. To support greenfield nodes, ACP as described in this
document needs to be combined with a bootstrap protocol and/or
mechanism that will enroll the node with the ACP keying material: the
ACP certificate and the TA. For ANI nodes, this protocol/mechanism
is BRSKI.
When such a node is powered on and determines that it is in
greenfield condition, it enables the bootstrap protocol(s) and/or
mechanism(s). Once the ACP keying material is enrolled, the
greenfield state ends and the ACP is started. When BRSKI is used,
the node's state reflects this by setting "ANI enable" upon
determination of greenfield state when it is powered on.
ACP greenfield nodes that, in the absence of ACP, would have their
interfaces in "down" state SHOULD set all native interfaces into
"admin down" state and only permit data plane traffic required for
the bootstrap protocol and/or mechanisms.
The ACP greenfield state ends either through the successful
enrollment of ACP keying material (certificate and TA) or the
detection of a permitted termination of ACP greenfield operations.
ACP nodes supporting greenfield operations MAY want to provide
backward compatibility with other forms of configuration and/or
provisioning, especially when only a subset of nodes are expected to
be deployed with ACP. Such an ACP node SHOULD observe attempts to
provision or configure the node via interfaces and/or methods that
traditionally indicate physical possession of the node, such as a
serial or USB console port or a USB memory stick with a bootstrap
configuration. When such an operation is observed before enrollment
of the ACP keying material has completed, the node SHOULD put itself
into the state the node would have been in if ACP/ANI was disabled at
boot. This terminates ACP greenfield operations.
When an ACP greenfield node enables multiple, automated ACP or non-
ACP enrollment and/or bootstrap protocols or mechanisms in parallel,
care must be taken not to terminate any protocol/mechanism before the
others either have succeeded in enrolling ACP keying material or have
progressed to a point of permitted termination for ACP greenfield
operations.
Highly secure ACP greenfield nodes may not permit any reason to
terminate ACP greenfield operations, including physical access.
Nodes that claim to support ANI greenfield operations SHOULD NOT
enable in parallel to BRSKI any enrollment/bootstrap protocol/
mechanism that allows Trust On First Use (TOFU, "Opportunistic
Security: Some Protection Most of the Time" [RFC7435]) over
interfaces other than those traditionally indicating physical
possession of the node. Protocols/mechanisms with published default
username/password authentication are considered to suffer from TOFU.
Securing the bootstrap protocol/mechanism by requiring a voucher
[RFC8366] can be used to avoid TOFU.
In summary, the goal of ACP greenfield support is to allow remote,
automated enrollment of ACP keying materials, and therefore automated
bootstrap into the ACP and to prohibit TOFU during bootstrap with the
likely exception (for backward compatibility) of bootstrapping via
interfaces traditionally indicating physical possession of the node.
9.3.6. Undoing "ANI/ACP enable"
Disabling ANI/ACP by undoing "ACP/ANI enable" is a risk for the
reliable operations of the ACP if it can be executed by mistake or
without authorization. This behavior could be influenced through
some additional (future) property in the certificate (e.g., in the
acp-node-name extension field): in an ANI deployment intended for
convenience, disabling it could be allowed without further
constraints. In an ANI deployment considered to be critical, more
checks would be required. One very controlled option would be to not
permit these commands unless the domain certificate has been revoked
or is denied renewal. Configuring this option would be a parameter
on the BRSKI registrar(s). As long as the node did not receive a
domain certificate, undoing "ANI/ACP enable" should not have any
additional constraints.
9.3.7. Summary
Node-wide "ACP/ANI enable [up-if-only]" commands enable the operation
of ACP/ANI. This is only auto-enabled on ANI greenfield devices,
otherwise it must be configured explicitly.
If the option "up-if-only" is not selected, interfaces enabled for
ACP/ANI interpret the "down" state as "admin down" and not "physical
down". In the "admin-down" state, all non-ACP/ANI packets are
filtered, but the physical layer is kept running to permit ACP/ANI to
operate.
(New) commands that result in physical interruption ("physical down",
"loopback") of ACP/ANI-enabled interfaces should be built to protect
continuance or reestablishment of ACP as much as possible.
Interface-level "ACP/ANI enable" commands control per-interface
operations. It is enabled by default on native interfaces and has to
be configured explicitly on other interfaces.
Disabling "ACP/ANI enable" globally and per interface should have
additional checks to minimize undesired breakage of ACP. The degree
of control could be a domain-wide parameter in the domain
certificates.
9.4. Partial or Incremental Adoption
The Zone Addressing Sub-Scheme (see Section 6.11.3) allows
incremental adoption of the ACP in a network where ACP can be
deployed on edge areas, but not across the core that is connecting
those edges.
In such a setup, each edge network, such as a branch or campus of an
enterprise network, has a disjoint ACP to which one or more unique
Zone-IDs are assigned: ACP nodes registered for a specific ACP zone
have to receive Zone Addressing Sub-Scheme addresses, for example, by
virtue of configuring for each such zone one or more ACP registrars
with that Zone-ID. All the registrars for these ACP zones need to
get ACP certificates from CAs relying on a common set of TAs and of
course the same ACP domain name.
These ACP zones can first be brought up as separate networks without
any connection between them and/or they can be connected across a
non-ACP enabled core network through various non-autonomic
operational practices. For example, each separate ACP zone can have
an edge node that is a L3 VPN PE (MPLS or IPv6 L3VPN), where a
complete non-autonomic ACP-Core VPN is created by using the ACP VRFs
and exchanging the routes from those ACP VRFs across the VPN's non-
autonomic routing protocol(s).
While such a setup is possible with any ACP addressing sub-scheme,
the Zone Addressing Sub-Scheme makes it easy to configure and
scalable for any VPN routing protocols because every ACP zone only
needs to indicate one or more /64 ACP zone addressing prefix routes
into the ACP-Core VPN as opposed to routes for every individual ACP
node as required in the other ACP addressing schemes.
Note that the non-autonomous ACP-Core VPN requires additional
extensions to propagate GRASP messages when GRASP discovery is
desired across the zones.
For example, one could set up on each zone edge router a remote ACP
tunnel to a GRASP hub. The GRASP hub could be implemented at the
application level and could run in the NOC of the network. It would
serve to propagate GRASP announcements between ACP zones and/or
generate GRASP announcements for NOC services.
Such a partial deployment may prove to be sufficient or could evolve
to become more autonomous through future standardized or nonstandard
enhancements, for example, by allowing GRASP messages to be
propagated across the L3VPN, leveraging for example L3VPN multicast
support.
Finally, these partial deployments can be merged into a single,
contiguous ACP that is completely autonomous (given appropriate ACP
support across the core) without changes in the cryptographic
material because the node's ACP certificates are from a single ACP.
9.5. Configuration and the ACP (Summary)
There is no desirable configuration for the ACP. Instead, all
parameters that need to be configured in support of the ACP are
limitations of the solution, but they are only needed in cases where
not all components are made autonomic. Wherever this is necessary,
it relies on preexisting mechanisms for configuration such as CLI or
YANG data models ("The YANG 1.1 Data Modeling Language" [RFC7950]).
The most important examples of such configuration include:
* When ACP nodes do not support an autonomic way to receive an ACP
certificate, for example, BRSKI, then such a certificate needs to
be configured via some preexisting mechanisms outside the scope of
this specification. Today, routers typically have a variety of
mechanisms to do this.
* Certificate maintenance requires PKI functions. Discovery of
these functions across the ACP is automated (see Section 6.2.5),
but their configuration is not.
* When non-ACP-capable nodes such as preexisting NMS need to be
physically connected to the ACP, the ACP node to which they attach
needs to be configured with ACP connect according to Section 8.1.
It is also possible to use that single physical connection to
connect both to the ACP and the data plane of the network as
explained in Section 8.1.4.
* When devices are not autonomically bootstrapped, explicit
configuration to enable the ACP needs to be applied. See
Section 9.3.
* When the ACP needs to be extended across interfaces other than L2,
the ACP as defined in this document cannot auto-discover candidate
neighbors automatically. Remote neighbors need to be configured,
see Section 8.2.
Once the ACP is operating, any further configuration for the data
plane can be done more reliably across the ACP itself because the ACP
provides addressing and connectivity (routing) independent of the
data plane. For this, the configuration methods simply need to allow
operating across the ACP VRF, for example, with NETCONF, SSH, or any
other method.
The ACP also provides additional security through its hop-by-hop
encryption for any such configuration operations. Some legacy
configuration methods (for example, SNMP, TFTP, or HTTP) may not use
end-to-end encryption, and most of the end-to-end secured
configuration methods still allow for easy, passive observation along
the path of the configuration taking place (for example, transport
flows, port numbers, and/or IP addresses).
The ACP can and should be used equally as the transport to configure
any of the aforementioned non-autonomic components of the ACP, but in
that case, the same caution needs to be exercised as with data plane
configuration without the ACP. Misconfiguration may cause the
configuring entity to be disconnected from the node it configures,
for example, when incorrectly unconfiguring a remote ACP neighbor
through which the configured ACP node is reached.
10. Summary: Benefits (Informative)
10.1. Self-Healing Properties
The ACP is self-healing:
* New neighbors will automatically join the ACP after successful
validation and will become reachable using their unique ULA
address across the ACP.
* When any changes happen in the topology, the routing protocol used
in the ACP will automatically adapt to the changes and will
continue to provide reachability to all nodes.
* The ACP tracks the validity of peer certificates and tears down
ACP secure channels when a peer certificate has expired. When
short-lived certificates with lifetimes on the order of OCSP/CRL
refresh times are used, then this allows for removal of invalid
peers (whose certificate was not renewed) at similar speeds as
when using OCSP/CRL. The same benefit can be achieved when using
CRL/OCSP, periodically refreshing the revocation information and
also tearing down ACP secure channels when the peer's (long-lived)
certificate is revoked. There is no requirement for ACP
implementations to require this enhancement, though, in order to
keep the mandatory implementations simpler.
The ACP can also sustain network partitions and mergers. Practically
all ACP operations are link local, where a network partition has no
impact. Nodes authenticate each other using the domain certificates
to establish the ACP locally. Addressing inside the ACP remains
unchanged, and the routing protocol inside both parts of the ACP will
lead to two working (although partitioned) ACPs.
There are a few central dependencies: a CRL may not be available
during a network partition. This can be addressed by a suitable
policy to not immediately disconnect neighbors when no CRL is
available. Also, an ACP registrar or CA might not be available
during a partition. This may delay renewal of certificates that are
to expire in the future, and it may prevent the enrollment of new
nodes during the partition.
Highly resilient ACP designs can be built by using ACP registrars
with embedded sub-CAs, as outlined in Section 9.2.4. As long as a
partition is left with one or more of such ACP registrars, it can
continue to enroll new candidate ACP nodes as long as the ACP
registrar's sub-CA certificate does not expire. Because the ACP
addressing relies on unique Registrar-IDs, a later merging of
partitions will not cause problems with ACP addresses assigned during
partitioning.
After a network partition, merging will just establish the previous
status: certificates can be renewed, the CRL is available, and new
nodes can be enrolled everywhere. Since all nodes use the same TA,
the merging will be smooth.
Merging two networks with different TAs requires the ACP nodes to
trust the union of TAs. As long as the routing-subdomain hashes are
different, the addressing will not overlap. Overlaps will only
happen accidentally in the unlikely event of a 40-bit hash collision
in SHA-256 (see Section 6.11). Note that the complete mechanisms to
merge networks is out of scope of this specification.
It is also highly desirable for an implementation of the ACP to be
able to run it over interfaces that are administratively down. If
this is not feasible, then it might instead be possible to request
explicit operator override upon administrative actions that would
administratively bring down an interface across which the ACP is
running, especially if bringing down the ACP is known to disconnect
the operator from the node. For example, any such administrative
down action could perform a dependency check to see if the transport
connection across which this action is performed is affected by the
down action (with default RPL routing used, packet forwarding will be
symmetric, so this is actually possible to check).
10.2. Self-Protection Properties
10.2.1. From the Outside
As explained in Section 6, the ACP is based on secure channels built
between nodes that have mutually authenticated each other with their
domain certificates. The channels themselves are protected using
standard encryption technologies such as DTLS or IPsec, which provide
additional authentication during channel establishment, data
integrity, and data confidentiality protection inside the ACP, and
also provide replay protection.
An attacker will not be able to join the ACP unless it has a valid
ACP certificate. An on-path attacker without a valid ACP certificate
cannot inject packets into the ACP due to ACP secure channels. An
attacker also cannot decrypt ACP traffic unless it can crack the
encryption. It can attempt behavioral traffic analysis on the
encrypted ACP traffic.
The degree to which compromised ACP nodes can impact the ACP depends
on the implementation of the ACP nodes and their impairment. When an
attacker has only gained administrative privileges to configure ACP
nodes remotely, the attacker can disrupt the ACP only through one of
the few configuration options to disable it (see Section 9.3) or by
the configuring of non-autonomic ACP options if those are supported
on the impaired ACP nodes (see Section 8). Injecting traffic into or
extracting traffic from an impaired ACP node is only possible when an
impaired ACP node supports ACP connect (see Section 8.1), and the
attacker can control traffic into/from one of the ACP node's
interfaces, such as by having physical access to the ACP node.
The ACP also serves as protection (through authentication and
encryption) for protocols relevant to OAM that may not have secured
protocol stack options or where implementation or deployment of those
options fail due to some vendor, product, or customer limitations.
This includes protocols such as SNMP ("An Architecture for Describing
Simple Network Management Protocol (SNMP) Management Frameworks"
[RFC3411]), NTP [RFC5905], PTP (Precision Time Protocol
[IEEE-1588-2008]), DNS ("DNS Extensions to Support IP Version 6"
[RFC3596]), DHCPv6 ("Dynamic Host Configuration Protocol for IPv6
(DHCPv6)" [RFC3315]), syslog ("The BSD Syslog Protocol" [RFC3164]),
RADIUS ("Remote Authentication Dial In User Service (RADIUS)"
[RFC2865]), Diameter ("Diameter Base Protocol" [RFC6733]), TACACS
("An Access Control Protocol, Sometimes Called TACACS" [RFC1492]),
IPFIX ("Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information" [RFC7011]), NetFlow
("Cisco Systems NetFlow Services Export Version 9" [RFC3954]) -- just
to name a few. Not all of these protocol references are necessarily
the latest version of protocols, but they are versions that are still
widely deployed.
Protection via the ACP secure hop-by-hop channels for these protocols
is meant to be only a stopgap, though: the ultimate goal is for these
and other protocols to use end-to-end encryption utilizing the domain
certificate and to rely on the ACP secure channels primarily for
zero-touch reliable connectivity, but not primarily for security.
The remaining attack vector would be to attack the underlying ACP
protocols themselves, either via directed attacks or by denial-of-
service attacks. However, as the ACP is built using link-local IPv6
addresses, remote attacks from the data plane are impossible as long
as the data plane has no facilities to remotely send IPv6 link-local
packets. The only exceptions are ACP-connected interfaces, which
require greater physical protection. The ULA addresses are only
reachable inside the ACP context and therefore unreachable from the
data plane. Also, the ACP protocols should be implemented to be
attack resistant and to not consume unnecessary resources even while
under attack.
10.2.2. From the Inside
The security model of the ACP is based on trusting all members of the
group of nodes that receive an ACP certificate for the same domain.
Attacks from the inside by a compromised group member are therefore
the biggest challenge.
Group members must be protected against attackers so that there is no
easy way to compromise them or use them as a proxy for attacking
other devices across the ACP. For example, management plane
functions (transport ports) should be reachable only from the ACP and
not from the data plane. This applies especially to those management
plane functions that lack secure end-to-end transport and to which
the ACP provides both automatic, reliable connectivity and protection
against attacks. Protection across all potential attack vectors is
typically easier to do in devices whose software is designed from the
beginning with the ACP in mind than in legacy, software-based systems
where the ACP is added on as another feature.
As explained above, traffic across the ACP should still be end-to-end
encrypted whenever possible. This includes traffic such as GRASP,
EST, and BRSKI inside the ACP. This minimizes man-in-the-middle
attacks by compromised ACP group members. Such attackers cannot
eavesdrop or modify communications, but they can just filter them
(which is unavoidable by any means).
See Appendix A.9.8 for further considerations on avoiding and dealing
with compromised nodes.
10.3. The Administrator View
An ACP is self-forming, self-managing, and self-protecting;
therefore, it has minimal dependencies on the administrator of the
network. Specifically, since it is (intended to be) independent of
configuration, there is only limited scope for configuration errors
on the ACP itself. The administrator may have the option to enable
or disable the entire approach, but detailed configuration is not
possible. This means that the ACP must not be reflected in the
running configuration of nodes, except for a possible on/off switch
(and even that is undesirable).
While configuration (except for Section 8 and Section 9.2) is not
possible, an administrator must have full visibility into the ACP and
all its parameters to be able to troubleshoot. Therefore, an ACP
must support all show and debug options, as with any other network
function. Specifically, an NMS or controller must be able to
discover the ACP and monitor its health. This visibility into ACP
operations must clearly be separated from the visibility of the data
plane so automated systems will never have to deal with ACP aspects
unless they explicitly desire to do so.
Since an ACP is self-protecting, a node that does not support the ACP
or that does not have a valid domain certificate cannot connect to
it. This means that by default a traditional controller or NMS
cannot connect to an ACP. See Section 8.1.1 for details on how to
connect an NMS host to the ACP.
11. Security Considerations
A set of ACP nodes with ACP certificates for the same ACP domain and
with ACP functionality enabled is automatically "self-building": the
ACP is automatically established between neighboring ACP nodes. It
is also self-protecting: the ACP secure channels are authenticated
and encrypted. No configuration is required for this.
The self-protecting property does not include workarounds for non-
autonomic components as explained in Section 8. See Section 10.2 for
details of how the ACP protects itself against attacks from the
outside and, to a more limited degree, from the inside as well.
However, the security of the ACP depends on a number of other
factors:
* The usage of domain certificates depends on a valid supporting PKI
infrastructure. If the chain of trust of this PKI infrastructure
is compromised, the security of the ACP is also compromised. This
is typically under the control of the network administrator.
* ACP nodes receive their certificates from ACP registrars. These
ACP registrars are security-critical dependencies of the ACP.
Procedures and protocols for ACP registrars are outside the scope
of this specification as explained in Section 6.11.7.1; only the
requirements for the resulting ACP certificates are specified.
* Every ACP registrar (for enrollment of ACP certificates) and ACP
EST server (for renewal of ACP certificates) is a security-
critical entity and its protocols are security-critical protocols.
Both need to be hardened against attacks, similar to a CA and its
protocols. A malicious registrar can enroll malicious nodes to an
ACP network (if the CA delegates this policy to the registrar) or
break ACP routing, for example, by assigning duplicate ACP
addresses to ACP nodes via their ACP certificates.
* ACP nodes that are ANI nodes rely on BRSKI as the protocol for ACP
registrars. For ANI-type ACP nodes, the security considerations
of BRSKI apply. It enables automated, secure enrollment of ACP
certificates.
* BRSKI and potentially other ACP registrar protocol options require
that nodes have an (X.509 v3 based) IDevID. IDevIDs are an option
for ACP registrars to securely identify candidate ACP nodes that
should be enrolled into an ACP domain.
* For IDevIDs to securely identify the node to which its IDevID is
assigned, the node needs (1) to utilize hardware support such as a
Trusted Platform Module (TPM) to protect against extraction and/or
cloning of the private key of the IDevID and (2) a hardware/
software infrastructure to prohibit execution of unauthenticated
software to protect against malicious use of the IDevID.
* Like the IDevID, the ACP certificate should equally be protected
from extraction or other abuse by the same ACP node
infrastructure. This infrastructure for IDevID and ACP
certificate is beneficial independent of the ACP registrar
protocol used (BRSKI or other).
* Renewal of ACP certificates requires support for EST; therefore,
the security considerations of [RFC7030] related to certificate
renewal and/or rekeying and TP renewal apply to the ACP. EST
security considerations when using other than mutual certificate
authentication do not apply, nor do considerations for initial
enrollment via EST apply, except for ANI-type ACP nodes because
BRSKI leverages EST.
* A malicious ACP node could declare itself to be an EST server via
GRASP across the ACP if malicious software could be executed on
it. The CA should therefore authenticate only known trustworthy
EST servers, such as nodes with hardware protections against
malicious software. When registrars use their ACP certificate to
authenticate towards a CA, the id-kp-cmcRA [RFC6402] extended key
usage attribute allows the CA to determine that the ACP node was
permitted during enrollment to act as an ACP registrar. Without
the ability to talk to the CA, a malicious EST server can still
attract ACP nodes attempting to renew their keying material, but
they will fail to perform successful renewal of a valid ACP
certificate. The ACP node attempting to use the malicious EST
server can then continue to use a different EST server and log a
failure against a malicious EST server.
* Malicious on-path ACP nodes may filter valid EST server
announcements across the ACP, but such malicious ACP nodes could
equally filter any ACP traffic such as the EST traffic itself.
Either attack requires the ability to execute malicious software
on an impaired ACP node, though.
* In the absence of malicious software injection, an attacker that
can misconfigure an ACP node that supports EST server
functionality could attempt to configure a malicious CA. This
would not result in the ability to successfully renew ACP
certificates, but it could result in DoS attacks by becoming an
EST server and by making ACP nodes attempt their ACP certificate
renewal via this impaired ACP node. This problem can be avoided
when the EST server implementation can verify that the configured
CA is indeed providing renewal for certificates of the node's ACP.
The ability to do so depends on the protocol between the EST
server and the CA, which is outside the scope of this document.
In summary, attacks against the PKI/certificate dependencies of the
ACP can be minimized by a variety of hardware and/or software
components, including options such as TPM for IDevID and/or ACP
certificate, prohibitions against the execution of untrusted
software, and design aspects of the EST server functionality for the
ACP that eliminate configuration-level impairment.
Because ACP peers select one out of potentially more than one
mutually supported ACP secure channel protocols via the approach
described in Section 6.6, ACP secure channel setup is subject to
downgrade attacks by MITM attackers. This can be discovered after
such an attack by additional mechanisms described in Appendix A.9.9.
Alternatively, more advanced channel selection mechanisms can be
devised.
The security model of the ACP as defined in this document is tailored
for use with private PKI. The TA of a private PKI provides the
security against maliciously created ACP certificates that give
access to an ACP. Such attacks can create fake ACP certificates with
correct-looking AcpNodeNames, but those certificates would not pass
the certificate path validation of the ACP domain membership check
(see Section 6.2.3, point 2).
There is no prevention of source-address spoofing inside the ACP.
This implies that if an attacker gains access to the ACP, it can
spoof all addresses inside the ACP and fake messages from any other
node. New protocols and/or services running across the ACP should
therefore use end-to-end authentication inside the ACP. This is
already done by GRASP as specified in this document.
The ACP is designed to enable automation of current network
management and the management of future autonomic peer-to-peer/
distributed networks. Any ACP member can send ACP IPv6 packets to
other ACP members and announce via ACP GRASP services to all ACP
members without depending on centralized components.
The ACP relies on peer-to-peer authentication and authorization using
ACP certificates. This security model is necessary to enable the
autonomic ad hoc, any-to-any connectivity between ACP nodes. It
provides infrastructure protection through hop-by-hop authentication
and encryption -- without relying on third parties. For any services
where this complete autonomic peer-to-peer group security model is
appropriate, the ACP certificate can also be used unchanged, for
example, for any type of data plane routing protocol security.
This ACP security model is designed primarily to protect against
attack from the outside, not against attacks from the inside. To
protect against spoofing attacks from compromised on-path ACP nodes,
end-to-end encryption inside the ACP is used by new ACP signaling:
GRASP across the ACP using TLS. The same is expected from any non-
legacy services or protocols using the ACP. Because no group keys
are used, there is no risk of impacted nodes accessing end-to-end
encrypted traffic from other ACP nodes.
Attacks from impacted ACP nodes against the ACP are more difficult
than against the data plane because of the autoconfiguration of the
ACP and the absence of configuration options that could be abused to
change or break ACP behavior. This is excluding configuration for
workaround in support of non-autonomic components.
Mitigation against compromised ACP members is possible through
standard automated certificate management mechanisms including
revocation and nonrenewal of short-lived certificates. In this
specification, there are no further optimizations of these mechanisms
defined for the ACP (but see Appendix A.9.8).
Higher-layer service built using ACP certificates should not solely
rely on undifferentiated group security when another model is more
appropriate or more secure. For example, central network
configuration relies on a security model where only a few especially
trusted nodes are allowed to configure the data plane of network
nodes (CLI, NETCONF). This can be done through ACP certificates by
differentiating them and introducing roles. See Appendix A.9.5.
Operators and developers of provisioning software need to be aware of
how the provisioning and configuration of network devices impacts the
ability of the operator and/or provisioning software to remotely
access the network nodes. By using the ACP, most of the issues of
provisioning/configuration causing connectivity loss of remote
provisioning and configuration will be eliminated, see Section 6.
Only a few exceptions, such as explicit physical interface down
configuration, will be left. See Section 9.3.2.
Many details of ACP are designed with security in mind and discussed
elsewhere in the document.
IPv6 addresses used by nodes in the ACP are covered as part of the
node's domain certificate as described in Section 6.2.2. This allows
even verification of ownership of a peer's IPv6 address when using a
connection authenticated with the domain certificate.
The ACP acts as a security (and transport) substrate for GRASP inside
the ACP such that GRASP is not only protected by attacks from the
outside, but also by attacks from compromised inside attackers -- by
relying not only on hop-by-hop security of ACP secure channels, but
also by adding end-to-end security for those GRASP messages. See
Section 6.9.2.
ACP provides for secure, resilient zero-touch discovery of EST
servers for certificate renewal. See Section 6.2.5.
ACP provides extensible, autoconfiguring hop-by-hop protection of the
ACP infrastructure via the negotiation of hop-by-hop secure channel
protocols. See Section 6.6.
The ACP is designed to minimize attacks from the outside by
minimizing its dependency on any non-ACP (data plane) operations and/
or configuration on a node. See also Section 6.13.2.
In combination with BRSKI, ACP enables a resilient, fully zero-touch
network solution for short-lived certificates that can be renewed or
reenrolled even after unintentional expiry (e.g., due to interrupted
connectivity). See Appendix A.2.
Because ACP secure channels can be long lived, but certificates used
may be short-lived, secure channels, for example, built via IPsec,
need to be terminated when peer certificates expire. See
Section 6.8.5.
Section 7.2 describes how to implement a routed ACP topology
operating on what effectively is a large bridge domain when using L3/
L2 routers that operate at L2 in the data plane. In this case, the
ACP is subject to a much higher likelihood of attacks by other nodes
"stealing" L2 addresses than in the actual routed case, especially
when the bridged network includes untrusted devices such as hosts.
This is a generic issue in L2 LANs. L2/L3 devices often already have
some form of "port security" to prohibit this. They rely on Neighbor
Discovery Protocol (NDP) or DHCP learning which port/MAC-address and
IPv6 address belong together and blocking MAC/IPv6 source addresses
from wrong ports. This type of function needs to be enabled to
prohibit DoS attacks and specifically to protect the ACP. Likewise,
the GRASP DULL instance needs to ensure that the IPv6 address in the
locator-option matches the source IPv6 address of the DULL GRASP
packet.
12. IANA Considerations
This document defines the "Autonomic Control Plane".
For the ANIMA-ACP-2020 ASN.1 module, IANA has assigned value 97 for
"id-mod-anima-acpnodename-2020" in the "SMI Security for PKIX Module
Identifier" (1.3.6.1.5.5.7.0) registry.
For the otherName / AcpNodeName, IANA has assigned value 10 for id-
on-AcpNodeName in the "SMI Security for PKIX Other Name Forms"
(1.3.6.1.5.5.7.8) registry.
IANA has registered the names in Table 2 in the "GRASP Objective
Names" subregistry of the "GeneRic Autonomic Signaling Protocol
(GRASP) Parameters" registry.
+================+==========================+
| Objective Name | Reference |
+================+==========================+
| AN_ACP | RFC 8994 (Section 6.4) |
+----------------+--------------------------+
| SRV.est | RFC 8994 (Section 6.2.5) |
+----------------+--------------------------+
Table 2: GRASP Objective Names
Explanation: this document chooses the initially strange looking
format "SRV.<service-name>" because these objective names would be in
line with potential future simplification of the GRASP objective
registry. Today, every name in the GRASP objective registry needs to
be explicitly allocated by IANA. In the future, this type of
objective names could be considered to be automatically registered in
that registry for the same service for which a <service-name> is
registered according to [RFC6335]. This explanation is solely
informational and has no impact on the requested registration.
IANA has created an "Autonomic Control Plane (ACP)" registry with the
subregistry, "ACP Address Type" (Table 3).
+=======+==================================+==================+
| Value | Description | Reference |
+=======+==================================+==================+
| 0 | ACP Zone Addressing Sub-Scheme/ | RFC 8994 |
| | ACP Manual Addressing Sub-Scheme | (Section 6.11.3, |
| | | Section 6.11.4) |
+-------+----------------------------------+------------------+
| 1 | ACP Vlong Addressing Sub-Scheme | RFC 8994 |
| | | (Section 6.11.5) |
+-------+----------------------------------+------------------+
| 2-3 | Unassigned | |
+-------+----------------------------------+------------------+
Table 3: Initial Values in the "ACP Address Type" Subregistry
The values in the "ACP Address Type" subregistry are numeric values
0..3 paired with a name (string). Future values MUST be assigned
using the Standards Action policy defined by "Guidelines for Writing
an IANA Considerations Section in RFCs" [RFC8126].
13. References
13.1. Normative References
[IKEV2IANA]
IANA, "Internet Key Exchange Version 2 (IKEv2)
Parameters",
<
https://www.iana.org/assignments/ikev2-parameters>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<
https://www.rfc-editor.org/info/rfc1034>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<
https://www.rfc-editor.org/info/rfc2119>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<
https://www.rfc-editor.org/info/rfc3810>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <
https://www.rfc-editor.org/info/rfc4191>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<
https://www.rfc-editor.org/info/rfc4193>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <
https://www.rfc-editor.org/info/rfc4291>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <
https://www.rfc-editor.org/info/rfc4301>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<
https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<
https://www.rfc-editor.org/info/rfc4862>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<
https://www.rfc-editor.org/info/rfc5234>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<
https://www.rfc-editor.org/info/rfc5246>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<
https://www.rfc-editor.org/info/rfc5280>.
[RFC5954] Gurbani, V., Ed., Carpenter, B., Ed., and B. Tate, Ed.,
"Essential Correction for IPv6 ABNF and URI Comparison in
RFC 3261", RFC 5954, DOI 10.17487/RFC5954, August 2010,
<
https://www.rfc-editor.org/info/rfc5954>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <
https://www.rfc-editor.org/info/rfc6347>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<
https://www.rfc-editor.org/info/rfc6550>.
[RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
and D. Barthel, "Routing Metrics Used for Path Calculation
in Low-Power and Lossy Networks", RFC 6551,
DOI 10.17487/RFC6551, March 2012,
<
https://www.rfc-editor.org/info/rfc6551>.
[RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing
Protocol for Low-Power and Lossy Networks (RPL)",
RFC 6552, DOI 10.17487/RFC6552, March 2012,
<
https://www.rfc-editor.org/info/rfc6552>.
[RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
Power and Lossy Networks (RPL) Option for Carrying RPL
Information in Data-Plane Datagrams", RFC 6553,
DOI 10.17487/RFC6553, March 2012,
<
https://www.rfc-editor.org/info/rfc6553>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<
https://www.rfc-editor.org/info/rfc7030>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <
https://www.rfc-editor.org/info/rfc7296>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <
https://www.rfc-editor.org/info/rfc7525>.
[RFC7676] Pignataro, C., Bonica, R., and S. Krishnan, "IPv6 Support
for Generic Routing Encapsulation (GRE)", RFC 7676,
DOI 10.17487/RFC7676, October 2015,
<
https://www.rfc-editor.org/info/rfc7676>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <
https://www.rfc-editor.org/info/rfc8174>.
[RFC8221] Wouters, P., Migault, D., Mattsson, J., Nir, Y., and T.
Kivinen, "Cryptographic Algorithm Implementation
Requirements and Usage Guidance for Encapsulating Security
Payload (ESP) and Authentication Header (AH)", RFC 8221,
DOI 10.17487/RFC8221, October 2017,
<
https://www.rfc-editor.org/info/rfc8221>.
[RFC8247] Nir, Y., Kivinen, T., Wouters, P., and D. Migault,
"Algorithm Implementation Requirements and Usage Guidance
for the Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 8247, DOI 10.17487/RFC8247, September 2017,
<
https://www.rfc-editor.org/info/rfc8247>.
[RFC8422] Nir, Y., Josefsson, S., and M. Pegourie-Gonnard, "Elliptic
Curve Cryptography (ECC) Cipher Suites for Transport Layer
Security (TLS) Versions 1.2 and Earlier", RFC 8422,
DOI 10.17487/RFC8422, August 2018,
<
https://www.rfc-editor.org/info/rfc8422>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<
https://www.rfc-editor.org/info/rfc8446>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <
https://www.rfc-editor.org/info/rfc8610>.
[RFC8990] Bormann, C., Carpenter, B., Ed., and B. Liu, Ed., "GeneRic
Autonomic Signaling Protocol (GRASP)", RFC 8990,
DOI 10.17487/RFC8990, May 2021,
<
https://www.rfc-editor.org/info/rfc8990>.
[RFC8995] Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
May 2021, <
https://www.rfc-editor.org/info/rfc8995>.
13.2. Informative References
[AR8021] IEEE, "IEEE Standard for Local and metropolitan area
networks - Secure Device Identity", IEEE 802.1AR,
<
https://1.ieee802.org/security/802-1ar>.
[CABFORUM] CA/Browser Forum, "Certificate Contents for Baseline SSL",
November 2019, <
https://cabforum.org/baseline-
requirements-certificate-contents/>.
[FCC] FCC, "June 15, 2020 T-Mobile Network Outage Report", A
Report of the Public Safety and Homeland Security Bureau
Federal Communications Commission, PS Docket No. 20-183,
October 2020, <
https://docs.fcc.gov/public/attachments/
DOC-367699A1.docx>.
[IEEE-1588-2008]
IEEE, "IEEE Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems",
DOI 10.1109/IEEESTD.2008.4579760, IEEE 1588-2008, July
2008,
<
https://standards.ieee.org/standard/1588-2008.html>.
[IEEE-802.1X]
IEEE, "IEEE Standard for Local and metropolitan area
networks--Port-Based Network Access Control",
DOI 10.1109/IEEESTD.2010.5409813, IEEE 802.1X-2010,
February 2010,
<
https://standards.ieee.org/standard/802_1X-2010.html>.
[LLDP] IEEE, "IEEE Standard for Local and metropolitan area
networks: Station and Media Access Control Connectivity
Discovery", DOI 10.1109/IEEESTD.2016.7433915, IEEE
802.1AB-2016, March 2016,
<
https://standards.ieee.org/standard/802_1AB-2016.html>.
[MACSEC] IEEE, "IEEE Standard for Local and Metropolitan Area
Networks: Media Access Control (MAC) Security",
DOI 10.1109/IEEESTD.2006.245590, IEEE 802.1AE-2006, August
2006,
<
https://standards.ieee.org/standard/802_1AE-2006.html>.
[NOC-AUTOCONFIG]
Eckert, T., Ed., "Autoconfiguration of NOC services in ACP
networks via GRASP", Work in Progress, Internet-Draft,
draft-eckert-anima-noc-autoconfig-00, 2 July 2018,
<
https://tools.ietf.org/html/draft-eckert-anima-noc-
autoconfig-00>.
[OP-TECH] Wikipedia, "Operational technology", October 2020,
<
https://en.wikipedia.org/w/
index.php?title=Operational_technology&oldid=986363045>.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, DOI 10.17487/RFC1112, August 1989,
<
https://www.rfc-editor.org/info/rfc1112>.
[RFC1492] Finseth, C., "An Access Control Protocol, Sometimes Called
TACACS", RFC 1492, DOI 10.17487/RFC1492, July 1993,
<
https://www.rfc-editor.org/info/rfc1492>.
[RFC1654] Rekhter, Y., Ed. and T. Li, Ed., "A Border Gateway
Protocol 4 (BGP-4)", RFC 1654, DOI 10.17487/RFC1654, July
1994, <
https://www.rfc-editor.org/info/rfc1654>.
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <
https://www.rfc-editor.org/info/rfc1918>.
[RFC2315] Kaliski, B., "PKCS #7: Cryptographic Message Syntax
Version 1.5", RFC 2315, DOI 10.17487/RFC2315, March 1998,
<
https://www.rfc-editor.org/info/rfc2315>.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998,
<
https://www.rfc-editor.org/info/rfc2409>.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, DOI 10.17487/RFC2865, June 2000,
<
https://www.rfc-editor.org/info/rfc2865>.
[RFC3164] Lonvick, C., "The BSD Syslog Protocol", RFC 3164,
DOI 10.17487/RFC3164, August 2001,
<
https://www.rfc-editor.org/info/rfc3164>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <
https://www.rfc-editor.org/info/rfc3315>.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
DOI 10.17487/RFC3411, December 2002,
<
https://www.rfc-editor.org/info/rfc3411>.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", STD 88,
RFC 3596, DOI 10.17487/RFC3596, October 2003,
<
https://www.rfc-editor.org/info/rfc3596>.
[RFC3954] Claise, B., Ed., "Cisco Systems NetFlow Services Export
Version 9", RFC 3954, DOI 10.17487/RFC3954, October 2004,
<
https://www.rfc-editor.org/info/rfc3954>.
[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
DOI 10.17487/RFC4007, March 2005,
<
https://www.rfc-editor.org/info/rfc4007>.
[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210,
DOI 10.17487/RFC4210, September 2005,
<
https://www.rfc-editor.org/info/rfc4210>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <
https://www.rfc-editor.org/info/rfc4364>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<
https://www.rfc-editor.org/info/rfc4429>.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<
https://www.rfc-editor.org/info/rfc4541>.
[RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet
Group Management Protocol Version 3 (IGMPv3) and Multicast
Listener Discovery Protocol Version 2 (MLDv2) for Source-
Specific Multicast", RFC 4604, DOI 10.17487/RFC4604,
August 2006, <
https://www.rfc-editor.org/info/rfc4604>.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<
https://www.rfc-editor.org/info/rfc4607>.
[RFC4610] Farinacci, D. and Y. Cai, "Anycast-RP Using Protocol
Independent Multicast (PIM)", RFC 4610,
DOI 10.17487/RFC4610, August 2006,
<
https://www.rfc-editor.org/info/rfc4610>.
[RFC4985] Santesson, S., "Internet X.509 Public Key Infrastructure
Subject Alternative Name for Expression of Service Name",
RFC 4985, DOI 10.17487/RFC4985, August 2007,
<
https://www.rfc-editor.org/info/rfc4985>.
[RFC5790] Liu, H., Cao, W., and H. Asaeda, "Lightweight Internet
Group Management Protocol Version 3 (IGMPv3) and Multicast
Listener Discovery Version 2 (MLDv2) Protocols", RFC 5790,
DOI 10.17487/RFC5790, February 2010,
<
https://www.rfc-editor.org/info/rfc5790>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<
https://www.rfc-editor.org/info/rfc5880>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<
https://www.rfc-editor.org/info/rfc5905>.
[RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
DOI 10.17487/RFC5912, June 2010,
<
https://www.rfc-editor.org/info/rfc5912>.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
March 2011, <
https://www.rfc-editor.org/info/rfc6120>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<
https://www.rfc-editor.org/info/rfc6241>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<
https://www.rfc-editor.org/info/rfc6335>.
[RFC6402] Schaad, J., "Certificate Management over CMS (CMC)
Updates", RFC 6402, DOI 10.17487/RFC6402, November 2011,
<
https://www.rfc-editor.org/info/rfc6402>.
[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
of Interpretation", RFC 6407, DOI 10.17487/RFC6407,
October 2011, <
https://www.rfc-editor.org/info/rfc6407>.
[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554,
DOI 10.17487/RFC6554, March 2012,
<
https://www.rfc-editor.org/info/rfc6554>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<
https://www.rfc-editor.org/info/rfc6724>.
[RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
Ed., "Diameter Base Protocol", RFC 6733,
DOI 10.17487/RFC6733, October 2012,
<
https://www.rfc-editor.org/info/rfc6733>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<
https://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<
https://www.rfc-editor.org/info/rfc6763>.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<
https://www.rfc-editor.org/info/rfc6824>.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<
https://www.rfc-editor.org/info/rfc6830>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<
https://www.rfc-editor.org/info/rfc7011>.
[RFC7404] Behringer, M. and E. Vyncke, "Using Only Link-Local
Addressing inside an IPv6 Network", RFC 7404,
DOI 10.17487/RFC7404, November 2014,
<
https://www.rfc-editor.org/info/rfc7404>.
[RFC7426] Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S.,
Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-
Defined Networking (SDN): Layers and Architecture
Terminology", RFC 7426, DOI 10.17487/RFC7426, January
2015, <
https://www.rfc-editor.org/info/rfc7426>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <
https://www.rfc-editor.org/info/rfc7435>.
[RFC7575] Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
Networking: Definitions and Design Goals", RFC 7575,
DOI 10.17487/RFC7575, June 2015,
<
https://www.rfc-editor.org/info/rfc7575>.
[RFC7576] Jiang, S., Carpenter, B., and M. Behringer, "General Gap
Analysis for Autonomic Networking", RFC 7576,
DOI 10.17487/RFC7576, June 2015,
<
https://www.rfc-editor.org/info/rfc7576>.
[RFC7585] Winter, S. and M. McCauley, "Dynamic Peer Discovery for
RADIUS/TLS and RADIUS/DTLS Based on the Network Access
Identifier (NAI)", RFC 7585, DOI 10.17487/RFC7585, October
2015, <
https://www.rfc-editor.org/info/rfc7585>.
[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016,
<
https://www.rfc-editor.org/info/rfc7721>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <
https://www.rfc-editor.org/info/rfc7761>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<
https://www.rfc-editor.org/info/rfc7950>.
[RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by
Hosts in a Multi-Prefix Network", RFC 8028,
DOI 10.17487/RFC8028, November 2016,
<
https://www.rfc-editor.org/info/rfc8028>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<
https://www.rfc-editor.org/info/rfc8126>.
[RFC8316] Nobre, J., Granville, L., Clemm, A., and A. Gonzalez
Prieto, "Autonomic Networking Use Case for Distributed
Detection of Service Level Agreement (SLA) Violations",
RFC 8316, DOI 10.17487/RFC8316, February 2018,
<
https://www.rfc-editor.org/info/rfc8316>.
[RFC8366] Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"A Voucher Artifact for Bootstrapping Protocols",
RFC 8366, DOI 10.17487/RFC8366, May 2018,
<
https://www.rfc-editor.org/info/rfc8366>.
[RFC8368] Eckert, T., Ed. and M. Behringer, "Using an Autonomic
Control Plane for Stable Connectivity of Network
Operations, Administration, and Maintenance (OAM)",
RFC 8368, DOI 10.17487/RFC8368, May 2018,
<
https://www.rfc-editor.org/info/rfc8368>.
[RFC8398] Melnikov, A., Ed. and W. Chuang, Ed., "Internationalized
Email Addresses in X.509 Certificates", RFC 8398,
DOI 10.17487/RFC8398, May 2018,
<
https://www.rfc-editor.org/info/rfc8398>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <
https://www.rfc-editor.org/info/rfc8402>.
[RFC8572] Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
Touch Provisioning (SZTP)", RFC 8572,
DOI 10.17487/RFC8572, April 2019,
<
https://www.rfc-editor.org/info/rfc8572>.
[RFC8684] Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
Paasch, "TCP Extensions for Multipath Operation with
Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
2020, <
https://www.rfc-editor.org/info/rfc8684>.
[RFC8739] Sheffer, Y., Lopez, D., Gonzalez de Dios, O., Pastor
Perales, A., and T. Fossati, "Support for Short-Term,
Automatically Renewed (STAR) Certificates in the Automated
Certificate Management Environment (ACME)", RFC 8739,
DOI 10.17487/RFC8739, March 2020,
<
https://www.rfc-editor.org/info/rfc8739>.
[RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves,
"Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 8981,
DOI 10.17487/RFC8981, February 2021,
<
https://www.rfc-editor.org/info/rfc8981>.
[RFC8992] Jiang, S., Ed., Du, Z., Carpenter, B., and Q. Sun,
"Autonomic IPv6 Edge Prefix Management in Large-Scale
Networks", RFC 8992, DOI 10.17487/RFC8992, May 2021,
<
https://www.rfc-editor.org/info/rfc8992>.
[RFC8993] Behringer, M., Ed., Carpenter, B., Eckert, T., Ciavaglia,
L., and J. Nobre, "A Reference Model for Autonomic
Networking", RFC 8993, DOI 10.17487/RFC8993, May 2021,
<
https://www.rfc-editor.org/info/rfc8993>.
[ROLL-APPLICABILITY]
Richardson, M., "ROLL Applicability Statement Template",
Work in Progress, Internet-Draft, draft-ietf-roll-
applicability-template-09, 3 May 2016,
<
https://tools.ietf.org/html/draft-ietf-roll-
applicability-template-09>.
[SR] Wikipedia, "Single-root input/output virtualization",
September 2020, <
https://en.wikipedia.org/w/
index.php?title=Single-root_input/
output_virtualization&oldid=978867619>.
[TLS-DTLS13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
dtls13-43, 30 April 2021,
<
https://tools.ietf.org/html/draft-ietf-tls-dtls13-43>.
[X.509] ITU-T, "Information technology - Open Systems
Interconnection - The Directory: Public-key and attribute
certificate frameworks", ITU-T Recommendation X.509,
October 2016, <
https://www.itu.int/rec/T-REC-X.509>.
[X.520] ITU-T, "Information technology - Open Systems
Interconnection - The Directory: Selected attribute
types", ITU-T Recommendation X.520, October 2016,
<
https://www.itu.int/rec/T-REC-X.520>.
Appendix A. Background and Future (Informative)
The following sections provide background information about aspects
of the normative parts of this document or associated mechanisms such
as BRSKI (such as why specific choices were made by the ACP), and
they discuss possible future variations of the ACP.
A.1. ACP Address Space Schemes
This document defines the Zone, Vlong, and Manual Addressing Sub-
Schemes primarily to support address prefix assignment via
distributed, potentially uncoordinated ACP registrars as defined in
Section 6.11.7. This costs a 48/46-bit identifier so that these ACP
registrars can assign nonconflicting address prefixes. This design
does not leave enough bits to simultaneously support a large number
of nodes (Node-ID), plus a large prefix of local addresses for every
node, plus a large enough set of bits to identify a routing zone. As
a result, the Zone and Vlong 8/16 Addressing Sub-Schemes attempt to
support all features but via separate prefixes.
In networks that expect always to rely on a centralized PMS as
described Section 9.2.5, the 48/46-bits for the Registrar-ID could be
saved. Such variations of the ACP addressing mechanisms could be
introduced through future work in different ways. If a new otherName
was introduced, incompatible ACP variations could be created where
every design aspect of the ACP could be changed, including all
addressing choices. If instead a new addressing sub-scheme would be
defined, it could be a backward-compatible extension of this ACP
specification. Information such as the size of a zone prefix and the
length of the prefix assigned to the ACP node itself could be encoded
via the extension field of the acp-node-name.
Note that an explicitly defined Manual Addressing Sub-Scheme is
always beneficial to provide an easy way for ACP nodes to prohibit
incorrect non-autonomic configuration of any non-"Manual" ACP address
spaces and therefore ensure that such non-autonomic operations will
never impact correct routing for any non-"Manual" ACP addresses
assigned via ACP certificates.
A.2. BRSKI Bootstrap (ANI)
BRSKI describes how nodes with an IDevID certificate can securely and
zero-touch enroll with an LDevID certificate to support the ACP.
BRSKI also leverages the ACP to enable zero-touch bootstrap of new
nodes across networks without any configuration requirements across
the transit nodes (e.g., no DHCP, DNS forwarding, and/or server
setup). This includes otherwise unconfigured networks as described
in Section 3.2. Therefore, BRSKI in conjunction with ACP provides
for a secure and zero-touch management solution for complete
networks. Nodes supporting such an infrastructure (BRSKI and ACP)
are called ANI nodes (Autonomic Networking Infrastructure), see
[RFC8993]. Nodes that do not support an IDevID certificate but only
an (insecure) vendor-specific Unique Device Identifier (UDI) or nodes
whose manufacturer does not support a MASA could use some future,
reduced-security version of BRSKI.
When BRSKI is used to provision a domain certificate (which is called
enrollment), the BRSKI registrar (acting as an enhanced EST server)
must include the otherName / AcpNodeName encoded ACP address and
domain name to the enrolling node (called a pledge) via its response
to the pledge's EST CSR Attributes Request that is mandatory in
BRSKI.
The CA in an ACP network must not change the otherName / AcpNodeName
in the certificate. The ACP nodes can therefore find their ACP
addresses and domain using this field in the domain certificate, both
for themselves as well as for other nodes.
The use of BRSKI in conjunction with the ACP can also help to further
simplify maintenance and renewal of domain certificates. Instead of
relying on CRL, the lifetime of certificates can be made extremely
small, for example, on the order of hours. When a node fails to
connect to the ACP within its certificate lifetime, it cannot connect
to the ACP to renew its certificate across it (using just EST), but
it can still renew its certificate as an "enrolled/expired pledge"
via the BRSKI bootstrap proxy. This requires only that the BRSKI
registrar honors expired domain certificates and that the pledge
attempts to perform TLS authentication for BRSKI bootstrap using its
expired domain certificate before falling back to attempting to use
its IDevID certificate for BRSKI. This mechanism could also render
CRLs unnecessary because the BRSKI registrar in conjunction with the
CA would not renew revoked certificates -- only a "Do-not-renew" list
would be necessary on the BRSKI registrar/CA.
In the absence of BRSKI or less secure variants thereof, the
provisioning of certificates may involve one or more touches or
nonstandardized automation. Node vendors usually support the
provisioning of certificates into nodes via PKCS #7 (see "PKCS #7:
Cryptographic Message Syntax Version 1.5" [RFC2315]) and may support
this provisioning through vendor-specific models via NETCONF
("Network Configuration Protocol (NETCONF)" [RFC6241]). If such
nodes also support NETCONF Zero Touch [RFC8572], then this can be
combined with zero-touch provisioning of domain certificates into
nodes. Unless there is the equivalent integration of NETCONF
connections across the ACP as there is in BRSKI, this combination
would not support zero-touch bootstrap across an unconfigured
network, though.
A.3. ACP Neighbor Discovery Protocol Selection
This section discusses why GRASP DULL was chosen as the discovery
protocol for L2-adjacent candidate ACP neighbors. The contenders
that were considered were GRASP, mDNS, and LLDP.
A.3.1. LLDP
LLDP and Cisco's earlier Cisco Discovery Protocol (CDP) are examples
of L2 discovery protocols that terminate their messages on L2 ports.
If those protocols had been chosen for ACP neighbor discovery, ACP
neighbor discovery would also have terminated on L2 ports. This
would have prevented ACP construction over non-ACP-capable, but LLDP-
or CDP-enabled L2 switches. LLDP has extensions using different MAC
addresses, and this could have been an option for ACP discovery as
well, but the additional required IEEE standardization and definition
of a profile for such a modified instance of LLDP seemed to be more
work than the benefit of "reusing the existing protocol" LLDP for
this very simple purpose.
A.3.2. mDNS and L2 Support
Multicast DNS (mDNS) "Multicast DNS" [RFC6762] with DNS Service
Discovery (DNS-SD) Resource Records (RRs) as defined in "DNS-Based
Service Discovery" [RFC6763] was a key contender as an ACP discovery
protocol. Because it relies on link-local IP multicast, it operates
at the subnet level and is also found in L2 switches. The authors of
this document are not aware of an mDNS implementation that terminates
its mDNS messages on L2 ports instead of on the subnet level. If
mDNS was used as the ACP discovery mechanism on an ACP-capable
(L3)/L2 switch as outlined in Section 7, then this would be necessary
to implement. It is likely that termination of mDNS messages could
only be applied to all mDNS messages from such a port, which would
then make it necessary to software forward any non-ACP-related mDNS
messages to maintain prior non-ACP mDNS functionality. Adding
support for ACP to such L2 switches with mDNS could therefore create
regression problems for prior mDNS functionality on those nodes.
With low performance of software forwarding in many L2 switches, this
could also make the ACP risky to support on such L2 switches.
A.3.3. Why DULL GRASP?
LLDP was not considered because of the above mentioned issues. mDNS
was not selected because of the above L2 mDNS considerations and
because of the following additional points.
If mDNS was not already existing in a node, it would be more work to
implement than DULL GRASP, and if an existing implementation of mDNS
was used, it would likely be more code space than a separate
implementation of DULL GRASP or a shared implementation of DULL GRASP
and GRASP in the ACP.
A.4. Choice of Routing Protocol (RPL)
This section motivates why RPL ("IPv6 Routing Protocol for Low-Power
and Lossy Networks [RFC6550]) was chosen as the default (and in this
specification only) routing protocol for the ACP. The choice and
above explained profile were derived from a pre-standard
implementation of ACP that was successfully deployed in operational
networks.
The requirements for routing in the ACP are the following:
* Self-management: the ACP must build automatically, without human
intervention. Therefore, the routing protocol must also work
completely automatically. RPL is a simple, self-managing
protocol, which does not require zones or areas; it is also self-
configuring, since configuration is carried as part of the
protocol (see Section 6.7.6 of [RFC6550]).
* Scale: the ACP builds over an entire domain, which could be a
large enterprise or service provider network. The routing
protocol must therefore support domains of 100,000 nodes or more,
ideally without the need for zoning or separation into areas. RPL
has this scale property. This is based on extensive use of
default routing.
* Low resource consumption: the ACP supports traditional network
infrastructure, thus runs in addition to traditional protocols.
The ACP, and specifically the routing protocol, must have low
resource consumption requirements, both in terms of memory and
CPU. Specifically, at edge nodes, where memory and CPU are
scarce, consumption should be minimal. RPL builds a DODAG, where
the main resource consumption is at the root of the DODAG. The
closer to the edge of the network, the less state needs to be
maintained. This adapts nicely to the typical network design.
Also, all changes below a common parent node are kept below that
parent node.
* Support for unstructured address space: in the ANI, node addresses
are identifiers, they and may not be assigned in a topological
way. Also, nodes may move topologically, without changing their
address. Therefore, the routing protocol must support completely
unstructured address space. RPL is specifically made for mobile,
ad hoc networks, with no assumptions on topologically aligned
addressing.
* Modularity: to keep the initial implementation small, yet allow
for more complex methods later, it is highly desirable that the
routing protocol has a simple base functionality, but can import
new functional modules if needed. RPL has this property with the
concept of "Objective Function", which is a plugin to modify
routing behavior.
* Extensibility: since the ANI is a new concept, it is likely that
changes to the way of operation will happen over time. RPL allows
for new Objective Functions to be introduced later, which allow
changes to the way the routing protocol creates the DAGs.
* Multi-topology support: it may become necessary in the future to
support more than one DODAG for different purposes, using
different Objective Functions. RPL allow for the creation of
several parallel DODAGs should this be required. This could be
used to create different topologies to reach different roots.
* No need for path optimization: RPL does not necessarily compute
the optimal path between any two nodes. However, the ACP does not
require this today, since it carries mainly delay-insensitive
feedback loops. It is possible that different optimization
schemes will become necessary in the future, but RPL can be
expanded (see "Extensibility" above).
A.5. ACP Information Distribution and Multicast
IP multicast is not used by the ACP because the ANI itself does not
require IP multicast but only service announcement/discovery. Using
IP multicast for that would have made it necessary to develop a zero-
touch autoconfiguring solution for ASM (Any Source Multicast - the
original form of IP multicast defined in "Host extensions for IP
multicasting" [RFC1112]), which would be quite complex and difficult
to justify. One aspect of complexity where no attempt at a solution
has been described in IETF documents is the automatic selection of
routers that should be PIM Sparse Mode (PIM-SM) Rendezvous Points
(RPs) (see "Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)" [RFC7761]). The other aspects of
complexity are the implementation of MLD ("Using Internet Group
Management Protocol Version 3 (IGMPv3) and Multicast Listener
Discovery Protocol Version 2 (MLDv2) for Source-Specific Multicast"
[RFC4604]), PIM-SM, and Anycast-RP (see "Anycast-RP Using Protocol
Independent Multicast (PIM)" [RFC4610]). If those implementations
already exist in a product, then they would be very likely tied to
accelerated forwarding, which consumes hardware resources, and that
in turn is difficult to justify as a cost of performing only service
discovery.
Some future ASA may need high-performance, in-network data
replication. That is the case when the use of IP multicast is
justified. Such an ASA can then use service discovery from ACP
GRASP, and then they do not need ASM but only SSM (see
"Source-Specific Multicast for IP" [RFC4607]) for the IP multicast
replication. SSM itself can simply be enabled in the data plane (or
even in an update to the ACP) without any configuration other than
just enabling it on all nodes, and it only requires a simpler version
of MLD (see "Lightweight Internet Group Management Protocol Version 3
(IGMPv3) and Multicast Listener Discovery Version 2 (MLDv2)
Protocols" [RFC5790]).
IGP routing protocols based on LSP (Link State Protocol) typically
have a mechanism to flood information, and such a mechanism could be
used to flood GRASP objectives by defining them to be information of
that IGP. This would be a possible optimization in future variations
of the ACP that do use an LSP-based routing protocol. Note though
that such a mechanism would not work easily for GRASP M_DISCOVERY
messages, which are intelligently (constrained) flooded not across
the whole ACP, but only up to a node where a responder is found. We
expect that many future services in the ASA will have only a few
consuming ASAs, and for those cases, the M_DISCOVERY method is more
efficient than flooding across the whole domain.
Because the ACP uses RPL, one desirable future extension is to use
RPL's existing notion of DODAG, which are loop-free distribution
trees, to make GRASP flooding more efficient both for M_FLOOD and
M_DISCOVERY. See Section 6.13.5 for how this will be specifically
beneficial when using NBMA interfaces. This is not currently
specified in this document because it is not quite clear yet what
exactly the implications are to make GRASP flooding depend on RPL
DODAG convergence and how difficult it would be to let GRASP flooding
access the DODAG information.
A.6. CAs, Domains, and Routing Subdomains
There is a wide range of setting up different ACP solutions by
appropriately using CAs and the domain and rsub elements in the acp-
node-name in the domain certificate. We summarize these options here
as they have been explained in different parts of the document and
discuss possible and desirable extensions.
An ACP domain is the set of all ACP nodes that can authenticate each
other as belonging to the same ACP network using the ACP domain
membership check (Section 6.2.3). GRASP inside the ACP is run across
all transitively connected ACP nodes in a domain.
The rsub element in the acp-node-name permits the use of addresses
from different ULA prefixes. One use case is the creation of
multiple physical networks that initially may be separated with one
ACP domain but different routing subdomains, so that all nodes can
mutually trust their ACP certificates (not depending on rsub) and so
that they could connect later together into a contiguous ACP network.
One instance of such a use case is an ACP for regions interconnected
via a non-ACP enabled core, for example, due to the absence of
product support for ACP on the core nodes. ACP connect
configurations as defined in this document can be used to extend and
interconnect those ACP islands to the NOC and merge them into a
single ACP when later that product support gap is closed.
Note that RPL scales very well. It is not necessary to use multiple
routing subdomains to scale ACP domains in a way that would be
required if other routing protocols where used. They exist only as
options for the above mentioned reasons.
If ACP domains need to be created that are not allowed to connect to
each other by default, simply use different domain elements in the
acp-node-name. These domain elements can be arbitrary, including
subdomains of one another: domains "example.com" and
"research.example.com" are separate domains if both are domain
elements in the acp-node-name of certificates.
It is not necessary to have a separate CA for different ACP domains:
an operator can use a single CA to sign certificates for multiple ACP
domains that are not allowed to connect to each other because the
checks for ACP adjacencies include the comparison of the domain part.
If multiple, independent networks chose the same domain name but had
their own CAs, these would not form a single ACP domain because of CA
mismatch. Therefore, there is no problem in choosing domain names
that are potentially also used by others. Nevertheless, it is highly
recommended to use domain names that have a high probability of being
unique. It is recommended to use domain names that start with a DNS
domain name owned by the assigning organization and unique within it,
for example, "acp.example.com" if you own "example.com".
A.7. Intent for the ACP
Intent is the architecture component of Autonomic Networks according
to [RFC8993] that allows operators to issue policies to the network.
Its applicability for use is quite flexible and freeform, with
potential applications including policies flooded across ACP GRASP
and interpreted on every ACP node.
One concern for future definitions of Intent solutions is the problem
of circular dependencies when expressing Intent policies about the
ACP itself.
For example, Intent could indicate the desire to build an ACP across
all domains that have a common parent domain (without relying on the
rsub/routing-subdomain solution defined in this document): ACP nodes
with the domains "example.com", "access.example.com",
"core.example.com", and "city.core.example.com" should all establish
one single ACP.
If each domain has its own source of Intent, then the Intent would
simply have to allow adding the peer domain's TA and domain names to
the parameters for the ACP domain membership check (Section 6.2.3) so
that nodes from those other domains are accepted as ACP peers.
If this Intent was to be originated only from one domain, it could
likely not be made to work because the other domains will not build
any ACP connections amongst each other, whether they use the same or
different CA due to the ACP domain membership check.
If the domains use the same CA, one could change the ACP setup to
permit the ACP to be established between two ACP nodes with different
acp-domain-names, but only for the purpose of disseminating limited
information, such as Intent, but not to set up full ACP connectivity,
specifically not RPL routing and passing of arbitrary GRASP
information, unless the Intent policies permit this to happen across
domain boundaries.
This type of approach, where the ACP first allows Intent to operate
and only then sets up the rest of ACP connectivity based on Intent
policy, could also be used to enable Intent policies that would limit
functionality across the ACP inside a domain, as long as no policy
would disturb the distribution of Intent, for example, to limit
reachability across the ACP to certain types of nodes or locations of
nodes.
A.8. Adopting ACP Concepts for Other Environments
The ACP as specified in this document is very explicit about the
choice of options to allow interoperable implementations. The
choices made may not be the best for all environments, but the
concepts used by the ACP can be used to build derived solutions.
The ACP specifies the use of ULA and the derivation of its prefix
from the domain name so that no address allocation is required to
deploy the ACP. The ACP will equally work using any other /48 IPv6
prefix and not ULA. This prefix could simply be a configuration of
the ACP registrars (for example, when using BRSKI) to enroll the
domain certificates, instead of the ACP registrar deriving the /48
ULA prefix from the AN domain name.
Some solutions may already have an auto-addressing scheme, for
example, derived from existing, unique device identifiers (e.g., MAC
addresses). In those cases, it may not be desirable to assign
addresses to devices via the ACP address information field in the way
described in this document. The certificate may simply serve to
identify the ACP domain, and the address field could be omitted. The
only fix required in the remaining way the ACP operates is to define
another element in the domain certificate for the two peers to decide
who is the Decider and who is the Follower during secure channel
building. Note though that future work may leverage the ACP address
to authenticate "ownership" of the address by the device. If the ACP
address used by a device is derived from some preexisting, permanent
local ID (such as MAC address), then it would be useful to store that
local ID also in the certificate.
The ACP is defined as a separate VRF because it intends to support
well-managed networks with a wide variety of configurations.
Therefore, reliable, configuration-indestructible connectivity cannot
be achieved from the data plane itself. In solutions where all
functions that impact transit connectivity are fully automated
(including security), indestructible, and resilient, it would be
possible to eliminate the need for the ACP to be a separate VRF.
Consider the most simple example system in which there is no separate
data plane, but the ACP is the data plane. Add BRSKI, and it becomes
a fully Autonomic Network -- except that it does not support
automatic addressing for user equipment. This gap can then be
closed, for example, by adding a solution derived from "Autonomic
IPv6 Edge Prefix Management in Large-Scale Networks" [RFC8992].
TCP/TLS as the protocols to provide reliability and security to GRASP
in the ACP may not be the preferred choice in constrained networks.
For example, CoAP/DTLS (Constrained Application Protocol) may be
preferred where they are already used, which would reduce the
additional code space footprint for the ACP on those devices. Hop-
by-hop reliability for ACP GRASP messages could be made to support
protocols like DTLS by adding the same type of negotiation as defined
in this document for ACP secure channel protocol negotiation. In
future ACP extensions meant to better support constrained devices,
end-to-end GRASP connections can be made to select their transport
protocol by indicating the supported transport protocols (e.g. TLS/
DTLS) via GRASP parameters of the GRASP objective through which the
transport endpoint is discovered.
RPL, the routing protocol used for the ACP, explicitly does not
optimize for shortest paths and fastest convergence. Variations of
the ACP may want to use a different routing protocol or introduce
more advanced RPL profiles.
Variations such as which routing protocol to use, or whether to
instantiate an ACP in a VRF or (as suggested above) as the actual
data plane, can be automatically chosen in implementations built to
support multiple options by deriving them from future parameters in
the certificate. Parameters in certificates should be limited to
those that would not need to be changed more often than that
certificates would need to be updated, or it should be ensured that
these parameters can be provisioned before the variation of an ACP is
activated in a node. Using BRSKI, this could be done, for example,
as additional follow-up signaling directly after the certificate
enrollment, still leveraging the BRSKI TLS connection and therefore
not introducing any additional connectivity requirements.
Last but not least, secure channel protocols including their
encapsulations are easily added to ACP solutions. ACP hop-by-hop
network-layer secure channels could also be replaced by end-to-end
security plus other means for infrastructure protection. Any future
network OAM should always use end-to-end security. By leveraging the
domain certificates, it would not be dependent on security provided
by ACP secure channels.
A.9. Further (Future) Options
A.9.1. Auto-Aggregation of Routes
Routing in the ACP according to this specification only leverages the
standard RPL mechanism of route optimization, e.g., keeping only the
routes that are not towards the RPL root. This is known to scale to
networks with 20,000 or more nodes. There is no auto-aggregation of
routes for /48 ULA prefixes (when using rsub in the acp-node-name)
and/or Zone-ID based prefixes.
Automatic assignment of Zone-ID and auto-aggregation of routes could
be achieved, for example, by configuring zone boundaries, announcing
via GRASP into the zones the zone parameters (Zone-ID and /48 ULA
prefix), and auto-aggregating routes on the zone boundaries. Nodes
would assign their Zone-ID and potentially even the /48 prefix based
on the GRASP announcements.
A.9.2. More Options for Avoiding IPv6 Data Plane Dependencies
As described in Section 6.13.2, the ACP depends on the data plane to
establish IPv6 link-local addressing on interfaces. Using a separate
MAC address for the ACP allows the full isolation of the ACP from the
data plane in a way that is compatible with this specification. It
is also an ideal option when using single-root input/output
virtualization (SR-IOV, see [SR]) in an implementation to isolate the
ACP because different SR-IOV interfaces use different MAC addresses.
When additional MAC address(es) are not available, separation of the
ACP could be done at different demux points. The same subnet
interface could have a separate IPv6 interface for the ACP and data
plane and therefore separate link-local addresses for both, where the
ACP interface is not configurable on the data plane. This too would
be compatible with this specification and not impact
interoperability.
An option that would require additional specification is to use a
different Ethertype from 0x86DD (IPv6) to encapsulate IPv6 packets
for the ACP. This would be a similar approach as used for IP
authentication packets in [IEEE-802.1X], which uses the Extensible
Authentication Protocol over Local Area Network (EAPoL) Ethertype
(0x88A2).
Note that in the case of ANI nodes, all of the above considerations
equally apply to the encapsulation of BRSKI packets including GRASP
used for BRSKI.
A.9.3. ACP APIs and Operational Models (YANG)
Future work should define a YANG data model [RFC7950] and/or node-
internal APIs to monitor and manage the ACP.
Support for the ACP adjacency table (Section 6.3) and ACP GRASP needs
to be included in such model and/or API.
A.9.4. RPL Enhancements
..... USA ...... ..... Europe ......
NOC1 NOC2
| |
| metric 100 |
ACP1 --------------------------- ACP2 .
| | . WAN
| metric 10 metric 20 | . Core
| | .
ACP3 --------------------------- ACP4 .
| metric 100 |
| | .
| | . Sites
ACP10 ACP11 .
Figure 17: Dual NOC
The profile for RPL specified in this document builds only one
spanning-tree path set to a root, typically a registrar in one NOC.
In the presence of multiple NOCs, routing toward the non-root NOCs
may be suboptimal. Figure 17 shows an extreme example. Assuming
that node ACP1 becomes the RPL root, traffic between ACP11 and NOC2
will pass through ACP4-ACP3-ACP1-ACP2 instead of ACP4-ACP2 because
the RPL-calculated DODAG and routes are shortest paths towards the
RPL root.
To overcome these limitations, extensions and/or modifications to the
RPL profile can optimize for multiple NOCs. This requires utilizing
data plane artifacts, including IP-in-IP encapsulation/decapsulation
on ACP routers and processing of IPv6 RPI headers. Alternatively,
(Src,Dst) routing table entries could be used.
Flooding of ACP GRASP messages can be further constrained and
therefore optimized by flooding only via links that are part of the
RPL DODAG.
A.9.5. Role Assignments
ACP connect is an explicit mechanism to "leak" ACP traffic explicitly
(for example, in a NOC). It is therefore also a possible security
gap when it is easy to enable ACP connect on arbitrary compromised
ACP nodes.
One simple solution is to define an extension in the ACP
certificate's ACP information field indicating the permission for ACP
connect to be configured on that ACP node. This could similarly be
done to decide whether a node is permitted to be a registrar or not.
Tying the permitted "roles" of an ACP node to the ACP certificate
provides fairly strong protection against misconfiguration, but it is
still subject to code modifications.
Another interesting role to assign to certificates is that of a NOC
node. This would allow the limiting of certain types of connections,
such as OAM TLS connections to only the NOC initiators or responders.
A.9.6. Autonomic L3 Transit
In this specification, the ACP can only establish autonomic
connectivity across L2 hops but requires non-autonomic configuration
to tunnel across L3 paths. Future work should specify mechanisms to
automatically tunnel ACP across L3 networks. A hub-and-spoke option
would allow tunneling across the Internet to a cloud or central
instance of the ACP; a peer-to-peer tunneling mechanism could tunnel
ACP islands across an L3VPN infrastructure.
A.9.7. Diagnostics
Section 9.1 describes diagnostics options that can be applied without
changing the external, interoperability-affecting characteristics of
ACP implementations.
Even better diagnostics of ACP operations are possible with
additional signaling extensions, such as the following:
1. Consider if LLDP should be a recommended functionality for ANI
devices to improve diagnostics, and if so, which information
elements it should signal (noting that such information is
conveyed in an insecure manner). This includes potentially new
information elements.
2. As an alternative to LLDP, a DULL GRASP diagnostics objective
could be defined to carry these information elements.
3. The IDevID certificate of BRSKI pledges should be included in the
selected insecure diagnostics option. This may be undesirable
when exposure of device information is seen as too much of a
security issue (the ability to deduce possible attack vectors
from device model, for example).
4. A richer set of diagnostics information should be made available
via the secured ACP channels, using either single-hop GRASP or
network-wide "topology discovery" mechanisms.
A.9.8. Avoiding and Dealing with Compromised ACP Nodes
Compromised ACP nodes pose the biggest risk to the operations of the
network. The most common types of compromise are the leakage of
credentials to manage and/or configure the device and the application
of malicious configuration, including the change of access
credentials, but not the change of software. Most of today's
networking equipment should have secure boot/software infrastructure
anyhow, so attacks that introduce malicious software should be a lot
harder.
The most important aspect of security design against these types of
attacks is to eliminate password-based configuration access methods
and instead rely on certificate-based credentials handed out only to
nodes where it is clear that the private keys cannot leak. This
limits unexpected propagation of credentials.
If password-based credentials to configure devices still need to be
supported, they must not be locally configurable, but only be
remotely provisioned or verified (through protocols like RADIUS or
Diameter), and there must be no local configuration permitting the
change of these authentication mechanisms, but ideally they should be
autoconfiguring across the ACP. See [NOC-AUTOCONFIG].
Without physical access to the compromised device, attackers with
access to configuration should not be able to break the ACP
connectivity, even when they can break or otherwise manipulate
(spoof) the data plane connectivity through configuration. To
achieve this, it is necessary to avoid providing configuration
options for the ACP, such as enabling/disabling it on interfaces.
For example, there could be an ACP configuration that locks down the
current ACP configuration unless factory reset is done.
With such means, the valid administration has the best chances to
maintain access to ACP nodes, to discover malicious configuration
though ongoing configuration tracking from central locations, for
example, and to react accordingly.
The primary reaction is to withdraw or change credentials, terminate
malicious existing management sessions, and fix the configuration.
Ensuring that management sessions using invalidated credentials are
terminated automatically without recourse will likely require new
work.
Only when these steps are infeasible, would it be necessary to revoke
or expire the ACP certificate credentials and consider the node
kicked off the network until the situation can be further rectified,
likely requiring direct physical access to the node.
Without extensions, compromised ACP nodes can only be removed from
the ACP at the speed of CRL/OCSP information refresh or expiry (and
non-removal) of short-lived certificates. Future extensions to the
ACP could, for example, use the GRASP flooding distribution of
triggered updates of CRL/OCSP or the explicit removal indication of
the compromised node's domain certificate.
A.9.9. Detecting ACP Secure Channel Downgrade Attacks
The following text proposes a mechanism to protect against downgrade
attacks without introducing a new specialized GRASP secure channel
mechanism. Instead, it relies on running GRASP after establishing a
secure channel protocol to verify if the established secure channel
option could have been the result of a MITM downgrade attack.
MITM attackers can force downgrade attacks for ACP secure channel
selection by filtering and/or modifying DULL GRASP messages and/or
actual secure channel data packets. For example, if at some point in
time, DTLS traffic could be more easily decrypted than traffic of
IKEv2, the MITM could filter all IKEv2 packets to force ACP nodes to
use DTLS (assuming that the ACP nodes in question supported both DTLS
and IKEv2).
For cases where such MITM attacks are not capable of injecting
malicious traffic (but only of decrypting the traffic), a downgrade
attack could be discovered after a secure channel connection is
established, for example, by using the following type of mechanism.
After the secure channel connection is established, the two ACP peers
negotiate, via an appropriate (to be defined) GRASP negotiation,
which ACP secure channel protocol should have been selected between
them (in the absence of a MITM attacker). This negotiation would
signal the ACP secure channel options announced by DULL GRASP by each
peer followed by an announcement of the preferred secure channel
protocol by the ACP peer that is the Decider in the secure channel
setup, i.e., the ACP peer that decides which secure channel protocol
to use. If that chosen secure channel protocol is different from the
one that actually was chosen, then this mismatch is an indication
that there is a MITM attacker or other similar issue (e.g., a
firewall prohibiting the use of specific protocols) that caused a
non-preferred secure channel protocol to be chosen. This discovery
could then result in mitigation options such as logging and ensuing
investigations.
Acknowledgements
This work originated from an Autonomic Networking project at Cisco
Systems, which started in early 2010. Many people contributed to
this project and the idea of the Autonomic Control Plane, amongst
whom (in alphabetical order): Ignas Bagdonas, Parag Bhide, Balaji BL,
Alex Clemm, Yves Hertoghs, Bruno Klauser, Max Pritikin, Michael
Richardson, and Ravi Kumar Vadapalli.
Special thanks to Brian Carpenter, Elwyn Davies, Joel Halpern, and
Sheng Jiang for their thorough reviews.
Many thanks to Ben Kaduk, Roman Danyliw, and Eric Rescorla for their
thorough SEC AD reviews, Russ Housley and Erik Kline for their
reviews, and to Valery Smyslov, Tero Kivinen, Paul Wouters, and Yoav
Nir for review of IPsec and IKEv2 parameters and helping to
understand those and other security protocol details better. Thanks
to Carsten Bormann for CBOR/CDDL help.
Further input, review, or suggestions were received from Rene Struik,
Benoit Claise, William Atwood, and Yongkang Zhang.
Contributors
For all things GRASP including validation code, ongoing document text
support, and technical input:
Brian Carpenter
School of Computer Science
University of Auckland
PB 92019
Auckland 1142
New Zealand
Email:
[email protected]
For RPL contributions and all things BRSKI/bootstrap including
validation code, ongoing document text support, and technical input:
Michael C. Richardson
Sandelman Software Works
Email:
[email protected]
URI:
http://www.sandelman.ca/mcr/
For the RPL technology choices and text:
Pascal Thubert
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 Mougins - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email:
[email protected]
Authors' Addresses
Toerless Eckert (editor)
Futurewei Technologies Inc. USA
2330 Central Expy
Santa Clara, CA 95050
United States of America
Email:
[email protected]
Michael H. Behringer (editor)
Email:
[email protected]
Steinthor Bjarnason
Arbor Networks
2727 South State Street, Suite 200
Ann Arbor, MI 48104
United States of America
Email:
[email protected]
