Internet Engineering Task Force (IETF) P. Pfister

Internet Engineering Task Force (IETF) P. Pfister
Request for Comments: 8801 É. Vyncke
Category: Standards Track Cisco
ISSN: 2070-1721 T. Pauly
Apple Inc.
D. Schinazi
Google LLC
W. Shao
Cisco
July 2020

Discovering Provisioning Domain Names and Data

Abstract

Provisioning Domains (PvDs) are defined as consistent sets of network
configuration information. PvDs allows hosts to manage connections
to multiple networks and interfaces simultaneously, such as when a
home router provides connectivity through both a broadband and
cellular network provider.

This document defines a mechanism for explicitly identifying PvDs
through a Router Advertisement (RA) option. This RA option announces
a PvD identifier, which hosts can compare to differentiate between
PvDs. The option can directly carry some information about a PvD and
can optionally point to PvD Additional Information that can be
retrieved using HTTP over TLS.

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/rfc8801.

Copyright Notice

Copyright (c) 2020 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction
1.1. Specification of Requirements
2. Terminology
3. Provisioning Domain Identification Using Router Advertisements
3.1. PvD Option for Router Advertisements
3.2. Router Behavior
3.3. Non-PvD-Aware Host Behavior
3.4. PvD-Aware Host Behavior
3.4.1. DHCPv6 Configuration Association
3.4.2. DHCPv4 Configuration Association
3.4.3. Connection Sharing by the Host
3.4.4. Usage of DNS Servers
4. Provisioning Domain Additional Information
4.1. Retrieving the PvD Additional Information
4.2. Operational Consideration to Providing the PvD Additional
Information
4.3. PvD Additional Information Format
4.3.1. Example
4.4. Detecting Misconfiguration and Misuse
5. Operational Considerations
5.1. Exposing Extra RA Options to PvD-Aware Hosts
5.2. Different RAs for PvD-Aware and Non-PvD-Aware Hosts
5.3. Enabling Multihoming for PvD-Aware Hosts
5.4. Providing Additional Information to PvD-Aware Hosts
6. Security Considerations
7. Privacy Considerations
8. IANA Considerations
8.1. Change to IPv6 Neighbor Discovery Option Formats Registry
8.2. New Entry in the Well-Known URIs Registry
8.3. New Additional Information PvD Keys Registry
8.4. New PvD Option Flags Registry
8.5. PvD JSON Media Type Registration
9. References
9.1. Normative References
9.2. Informative References
Acknowledgments
Authors' Addresses

1. Introduction

Provisioning Domains (PvDs) are defined in [RFC7556] as consistent
sets of network configuration information. This information includes
properties that are traditionally associated with a single networking
interface, such as source addresses, DNS configuration, proxy
configuration, and gateway addresses.

Clients that are aware of PvDs can take advantage of multiple network
interfaces simultaneously. This enables using two PvDs in parallel
for separate connections or for multi-path transports.

While most PvDs today are discovered implicitly (such as by receiving
information via Router Advertisements from a router on a network that
a client host directly connects to), [RFC7556] also defines the
notion of Explicit PvDs. IPsec Virtual Private Networks are
considered Explicit PvDs, but Explicit PvDs can also be discovered
via the local network router. Discovering Explicit PvDs allows two
key advancements in managing multiple PvDs:

1. The ability to discover and use multiple PvDs on a single
interface, such as when a local router can provide connectivity
to two different Internet Service Providers.

2. The ability to associate Additional Information about PvDs to
describe the properties of the network.

While [RFC7556] defines the concept of Explicit PvDs, it does not
define the mechanism for discovering multiple Explicit PvDs on a
single network and their Additional Information.

This document specifies a way to identify PvDs with Fully Qualified
Domain Names (FQDNs), called PvD IDs. Those identifiers are
advertised in a new Router Advertisement (RA) [RFC4861] option called
the PvD Option, which, when present, associates the PvD ID with all
the information present in the Router Advertisement as well as any
configuration object, such as addresses, derived from it. The PvD
Option may also contain a set of other RA options, along with an
optional inner Router Advertisement message header. These options
and optional inner header are only visible to 'PvD-aware' hosts,
allowing such hosts to have a specialized view of the network
configuration.

Since PvD IDs are used to identify different ways to access the
Internet, multiple PvDs (with different PvD IDs) can be provisioned
on a single host interface. Similarly, the same PvD ID could be used
on different interfaces of a host in order to inform that those PvDs
ultimately provide equivalent services.

This document also introduces a mechanism for hosts to retrieve
optional Additional Information related to a specific PvD by means of
an HTTP-over-TLS query using a URI derived from the PvD ID. The
retrieved JSON object contains Additional Information that would
typically be considered too large to be directly included in the
Router Advertisement but might be considered useful to the
applications, or even sometimes users, when choosing which PvD should
be used.

For example, if Alice has both a cellular network provider and a
broadband provider in her home, her PvD-aware devices and
applications would be aware of both available uplinks. These
applications could fail-over between these networks or run
connections over both (potentially using multi-path transports).
Applications could also select specific uplinks based on the
properties of the network; for example, if the cellular network
provides free high-quality video streaming, a video-streaming
application could select that network while most of the other traffic
on Alice's device uses the broadband provider.

1.1. Specification of Requirements

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.

2. Terminology

This document uses the following terminology:

Provisioning Domain (PvD): A set of network configuration
information; for more information, see [RFC7556].

PvD ID: A Fully Qualified Domain Name (FQDN) used to identify a PvD.

Explicit PvD: A PvD uniquely identified with a PvD ID. For more
information, see [RFC7556].

Implicit PvD: A PvD that, in the absence of a PvD ID, is identified
by the host interface to which it is attached and the address of
the advertising router. See also [RFC7556].

PvD-aware host: A host that supports the association of network
configuration information into PvDs and the use of these PvDs as
described in this document. Also named "PvD-aware node" in
[RFC7556].

3. Provisioning Domain Identification Using Router Advertisements

Explicit PvDs are identified by a PvD ID. The PvD ID is a Fully
Qualified Domain Name (FQDN) that identifies the network operator.
Network operators MUST use names that they own or manage to avoid
naming conflicts. The same PvD ID MAY be used in several access
networks when they ultimately provide identical services (e.g., in
all home networks subscribed to the same service); else, the PvD ID
MUST be different to follow Section 2.4 of [RFC7556].

3.1. PvD Option for Router Advertisements

This document introduces a Router Advertisement (RA) option called
the PvD Option. It is used to convey the FQDN identifying a given
PvD (see Figure 1), bind the PvD ID with configuration information
received over DHCPv4 (see Section 3.4.2), enable the use of HTTP over
TLS to retrieve the PvD Additional Information JSON object (see
Section 4), as well as contain any other RA options that would
otherwise be valid in the RA.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |H|L|R| Reserved | Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
... PvD ID FQDN ...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...
... Router Advertisement message header ...
... (Only present when R-flag is set) ...
... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-

Figure 1: PvD Option Format

Type: (8 bits) Set to 21.

Length: (8 bits) The length of the option in units of 8 octets,
including the Type and Length fields, the Router Advertisement
message header, if any, as well as the RA options that are
included within the PvD Option.

H-flag: (1 bit) 'HTTP' flag stating whether some PvD Additional
Information is made available through HTTP over TLS, as described
in Section 4.

L-flag: (1 bit) 'Legacy' flag stating whether the PvD is associated
with IPv4 information assigned using DHCPv4 (see Section 3.4.2).

R-flag: (1 bit) 'Router Advertisement' flag stating whether the PvD
Option header is followed (right after padding to the next 64-bit
boundary) by a Router Advertisement message header (see
Section 4.2 of [RFC4861]). The usage of the inner message header
is described in Section 3.4.

Reserved: (9 bits) Reserved for later use. It MUST be set to zero
by the sender and ignored by the receiver.

Delay: (4 bits) Unsigned integer used to delay HTTP GET queries from
hosts by a randomized backoff (see Section 4.1). If the H-flag is
not set, senders SHOULD set the delay to zero, and receivers
SHOULD ignore the value.

Sequence Number: (16 bits) Sequence number for the PvD Additional
Information, as described in Section 4. If the H-flag is not set,
senders SHOULD set the Sequence Number to zero, and receivers
SHOULD ignore the value.

PvD ID FQDN: The FQDN used as PvD ID encoded in DNS format, as
described in Section 3.1 of [RFC1035]. Domain name compression as
described in Section 4.1.4 of [RFC1035] MUST NOT be used.

Padding: Zero or more padding octets to the next 8-octet boundary
(see Section 4.6 of [RFC4861]). It MUST be set to zero by the
sender and ignored by the receiver.

RA message header: (16 octets) When the R-flag is set, a full Router
Advertisement message header as specified in [RFC4861]. The
sender MUST set the Type field to 134 (the value for "Router
Advertisement") and set the Code field to 0. Receivers MUST
ignore both of these fields. The Checksum field MUST be set to 0
by the sender; non-zero checksums MUST be ignored by the receiver
without causing the processing of the message to fail. All other
fields are to be set and parsed as specified in [RFC4861] or any
updating documents.

Options: Zero or more RA options that would otherwise be valid as
part of the Router Advertisement main body but are instead
included in the PvD Option so as to be ignored by hosts that are
not PvD aware.

Figure 2 shows an example of a PvD Option with "example.org" as the
PvD ID FQDN and includes both a Recursive DNS Server (RDNSS) option
and a Prefix Information Option. It has a Sequence Number of 123 and
indicates the presence of PvD Additional Information that is expected
to be fetched with a delay factor of 1.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
| Type: 21 | Length: 12 |1|0|0| Reserved |Delay:1|
+---------------+-------------------------------+---------------+
| Seq number: 123 | 7 | e |
+---------------+-----------------------------------------------+
| x | a | m | p |
+---------------------------------------------------------------+
| l | e | 3 | o |
+---------------------------------------------------------------+
| r | g | 0 | 0 (padding) |
+---------------------------------------------------------------+
| 0 (padding) | 0 (padding) | 0 (padding) | 0 (padding) |
+---------------+---------------+---------------+---------------+
| RDNSS option (RFC 8106) length: 5 ...
... ...
... |
+---------------------------------------------------------------+
| Prefix Information Option (RFC 4861) length: 4 ...
... |
... |
+---------------------------------------------------------------+

Figure 2: Example PvD Option

3.2. Router Behavior

A router MAY send RAs containing one PvD Option but MUST NOT include
more than one PvD Option in each RA. The PvD Option MUST NOT contain
further PvD Options.

The PvD Option MAY contain zero, one, or more RA options that would
otherwise be valid as part of the same RA. Such options are
processed by PvD-aware hosts and ignored by other hosts as per
Section 4.2 of [RFC4861].

In order to provide multiple different PvDs, a router MUST send
multiple RAs. RAs sent from different link-local source addresses
establish distinct Implicit PvDs in the absence of a PvD Option.
Explicit PvDs MAY share link-local source addresses with an Implicit
PvD and any number of other Explicit PvDs.

In other words, different Explicit PvDs MAY be advertised with RAs
using the same link-local source address, but different Implicit
PvDs, advertised by different RAs, MUST use different link-local
addresses because these Implicit PvDs are identified by the source
addresses of the RAs. If a link-local address on the router is
changed, then any new RA will be interpreted as a different Implicit
PvD by PvD-aware hosts.

As specified in [RFC4861] and [RFC6980], when the set of options
causes the size of an advertisement to exceed the link MTU, multiple
router advertisements MUST be sent to avoid fragmentation, each
containing a subset of the options. In such cases, the PvD Option
header (i.e., all fields except the Options field) MUST be repeated
in all the transmitted RAs. The options within the Options field MAY
be transmitted only once, included in one of the transmitted PvD
Options.

3.3. Non-PvD-Aware Host Behavior

As the PvD Option has a new option code, non-PvD-aware hosts will
simply ignore the PvD Option and all the options it contains (see
Section 4.2 of [RFC4861]). This ensures the backward compatibility
required in Section 3.3 of [RFC7556]. This behavior allows for a
mixed-mode network where a mix of PvD-aware and non-PvD-aware hosts
coexist.

3.4. PvD-Aware Host Behavior

Hosts MUST associate received RAs and included configuration
information (e.g., Router Valid Lifetime, Prefix Information
[RFC4861], Recursive DNS Server [RFC8106], and Routing Information
[RFC4191] options) with the Explicit PvD identified by the first PvD
Option present in the received RA, if any, or with the Implicit PvD
identified by the host interface and the source address of the
received RA otherwise. If an RA message header is present both
within the PvD Option and outside it, the header within the PvD
Option takes precedence.

In case multiple PvD Options are found in a given RA, hosts MUST
ignore all but the first PvD Option.

If a host receives PvD Options flags that it does not recognize
(currently in the Reserved field), it MUST ignore these flags.

Similarly, hosts MUST associate all network configuration objects
(e.g., default routers, addresses, more specific routes, and DNS
Recursive Resolvers) with the PvD associated with the RA that
provisioned the object. For example, addresses that are generated
using a received Prefix Information Option (PIO) are associated with
the PvD of the last received RA that included the given PIO.

PvD IDs MUST be compared in a case-insensitive manner as defined by
[RFC4343]. For example, "pvd.example.com." or "PvD.Example.coM."
would refer to the same PvD.

While performing PvD-specific operations such as resolving names,
executing the default address selection algorithm [RFC6724], or
executing the default router selection algorithm when forwarding
packets [RFC4861] [RFC4191] [RFC8028], hosts and applications MAY
consider only the configuration associated with any non-empty subset
of PvDs. For example, a host MAY associate a given process with a
specific PvD, or a specific set of PvDs, while associating another
process with another PvD. A PvD-aware application might also be able
to select, on a per-connection basis, which PvDs should be used. In
particular, constrained devices such as small battery-operated
devices (e.g., Internet of Things (IoT)) or devices with limited CPU
or memory resources may purposefully use a single PvD while ignoring
some received RAs containing different PvD IDs.

The way an application expresses its desire to use a given PvD, or a
set of PvDs, and the way this selection is enforced are out of the
scope of this document. Useful insights about these considerations
can be found in [MPVD-API].

3.4.1. DHCPv6 Configuration Association

When a host retrieves stateless configuration elements using DHCPv6
(e.g., DNS recursive resolvers or DNS domain search lists [RFC3646]),
they MUST be associated with all the Explicit and Implicit PvDs
received on the same interface and contained in an RA with the O-flag
set [RFC4861].

When a host retrieves stateful assignments using DHCPv6, such
assignments MUST be associated with the received PvD that was
received with RAs with the M-flag set and including a matching PIO.
A PIO is considered to match a DHCPv6 assignment when the IPv6 prefix
from the PIO includes the assignment from DHCPv6. For example, if a
PvD's associated PIO defines the prefix "2001:db8:cafe::/64", a
DHCPv6 IA_NA message that assigns the address
"2001:db8:cafe::1234:4567" would be considered to match.

In cases where an address would be assigned by DHCPv6 and no matching
PvD could be found, hosts MAY associate the assigned address with any
Implicit PvD received on the same interface or to multiple Implicit
PvDs received on the same interface. This is intended to resolve
backward-compatibility issues with rare deployments choosing to
assign addresses with DHCPv6 while not sending any matching PIO.
Implementations are suggested to flag or log such scenarios as errors
to help detect misconfigurations.

3.4.2. DHCPv4 Configuration Association

Associating DHCPv4 [RFC2131] configuration elements with Explicit
PvDs allows hosts to treat a set of IPv4 and IPv6 configurations as a
single PvD with shared properties. For example, consider a router
that provides two different uplinks. One could be a broadband
network that has data rate and streaming properties described in PvD
Additional Information and that provides both IPv4 and IPv6 network
access. The other could be a cellular network that provides only
IPv6 network access and uses NAT64 [RFC6146]. The broadband network
can be represented by an Explicit PvD that points to the Additional
Information and also marks association with DHCPv4 information. The
cellular network can be represented by a different Explicit PvD that
is not associated with DHCPv4.

When a PvD-aware host retrieves configuration elements from DHCPv4,
the information is associated either with a single Explicit PvD on
that interface or else with all Implicit PvDs on the same interface.

An Explicit PvD indicates its association with DHCPv4 information by
setting the L-flag in the PvD Option. If there is exactly one
Explicit PvD that sets this flag, hosts MUST associate the DHCPv4
information with that PvD. Multiple Explicit PvDs on the same
interface marking this flag is a misconfiguration, and hosts SHOULD
NOT associate the DHCPv4 information with any Explicit PvD in this
case.

If no single Explicit PvD claims association with DHCPv4, the
configuration elements coming from DHCPv4 MUST be associated with all
Implicit PvDs identified by the interface on which the DHCPv4
transaction happened. This maintains existing host behavior.

3.4.3. Connection Sharing by the Host

The situation in which a host shares connectivity from an upstream
interface (e.g., cellular) to a downstream interface (e.g., Wi-Fi) is
known as 'tethering'. Techniques such as ND Proxy [RFC4389], 64share
[RFC7278], or prefix delegation (e.g., using DHCPv6-PD [RFC8415]) may
be used for that purpose.

Whenever the RAs received from the upstream interface contain a PvD
Option, hosts that are sharing connectivity SHOULD include a PvD
Option within the RAs sent downstream with:

* The same PvD ID FQDN

* The same H-flag, Delay, and Sequence Number values

* The L-flag set whenever the host is sharing IPv4 connectivity
received from the same upstream interface

* The bits in the Reserved field set to 0

The values of the R-flag, Router Advertisement message header, and
Options field depend on whether or not the connectivity should be
shared only with PvD-aware hosts (see Section 3.2). In particular,
all options received within the upstream PvD Option and included in
the downstream RA SHOULD be included in the downstream PvD Option.

3.4.4. Usage of DNS Servers

PvD-aware hosts can be provisioned with recursive DNS servers via RA
options passed within an Explicit PvD, via RA options associated with
an Implicit PvD, via DHCPv6 or DHCPv4, or from some other
provisioning mechanism that creates an Explicit PvD (such as a VPN).
In all of these cases, the recursive DNS server addresses SHOULD be
associated with the corresponding PvD. Specifically, queries sent to
a configured recursive DNS server SHOULD be sent from a local IP
address that was provisioned for the PvD via RA or DHCP. Answers
received from the DNS server SHOULD only be used on the same PvD.

PvD-aware applications will be able to select which PvD(s) to use for
DNS resolution and connections, which allows them to effectively use
multiple Explicit PvDs. In order to support non-PvD-aware
applications, however, PvD-aware hosts SHOULD ensure that non-PvD-
aware name resolution APIs like "getaddrinfo" only use resolvers from
a single PvD for a given query. Handling DNS across PvDs is
discussed in Section 5.2.1 of [RFC7556], and PvD APIs are discussed
in Section 6 of [RFC7556].

Maintaining the correct usage of DNS within PvDs avoids various
practical errors such as:

* A PvD associated with a VPN or otherwise private network may
provide DNS answers that contain addresses inaccessible over
another PvD. This includes the DNS queries to retrieve PvD
Additional Information, which could otherwise send identifying
information to the recursive DNS system (see Section 4.1).

* A PvD that uses a NAT64 [RFC6146] and DNS64 [RFC6147] will
synthesize IPv6 addresses in DNS answers that are not globally
routable and would be invalid on other PvDs. Conversely, an IPv4
address resolved via DNS on another PvD cannot be directly used on
a NAT64 network.

4. Provisioning Domain Additional Information

Additional information about the network characteristics can be
retrieved based on the PvD ID. This set of information is called PvD
Additional Information and is encoded as a JSON object [RFC8259].
This JSON object is restricted to the Internet JSON (I-JSON) profile,
as defined in [RFC7493].

The purpose of this JSON object is to provide Additional Information
to applications on a client host about the connectivity that is
provided using a given interface and source address. It typically
includes data that would be considered too large, or not critical
enough, to be provided within an RA option. The information
contained in this object MAY be used by the operating system, network
libraries, applications, or users in order to decide which set of
PvDs should be used for which connection, as described in
Section 3.4.

The Additional Information related to a PvD is specifically intended
to be optional and is targeted at optimizing or informing the
behavior of user-facing hosts. This information can be extended to
provide hints for host system behavior (such as captive portal or
walled-garden PvD detection) or application behavior (describing
application-specific services offered on a given PvD). This content
may not be appropriate for light-weight IoT devices. IoT devices
might need only a subset of the information and would in some cases
prefer a smaller representation like Concise Binary Object
Representation (CBOR) [RFC7049]. Delivering a reduced version of the
PvD Additional Information designed for such devices is not defined
in this document.

4.1. Retrieving the PvD Additional Information

When the H-flag of the PvD Option is set, hosts MAY attempt to
retrieve the PvD Additional Information associated with a given PvD
by performing an HTTP-over-TLS [RFC2818] GET query to "https://<PvD-
ID>/.well-known/pvd". Inversely, hosts MUST NOT do so whenever the
H-flag is not set.

Recommendations for how to use TLS securely can be found in
[RFC7525].

When a host retrieves the PvD Additional Information, it MUST verify
that the TLS server certificate is valid for the performed request,
specifically, that a DNS-ID [RFC6125] on the certificate is equal to
the PvD ID expressed as an FQDN. This validation indicates that the
owner of the FQDN authorizes its use with the prefix advertised by
the router. If this validation fails, hosts MUST close the
connection and treat the PvD as if it has no Additional Information.

HTTP requests and responses for PvD Additional Information use the
"application/pvd+json" media type (see Section 8.5). Clients SHOULD
include this media type as an Accept header field in their GET
requests, and servers MUST mark this media type as their Content-Type
header field in responses.

Note that the DNS name resolution of the PvD ID, any connections made
for certificate validation (such as Online Certificate Status
Protocol (OCSP) [RFC6960]), and the HTTP request itself MUST be
performed using the considered PvD. In other words, the name
resolution, PKI checks, source address selection, as well as the
next-hop router selection MUST be performed while exclusively using
the set of configuration information attached with the PvD, as
defined in Section 3.4. In some cases, it may therefore be necessary
to wait for an address to be available for use (e.g., once the
Duplicate Address Detection or DHCPv6 processes are complete) before
initiating the HTTP-over-TLS query. In order to address privacy
concerns around linkability of the PvD HTTP connection with future
user-initiated connections, if the host has a temporary address per
[RFC4941] in this PvD, then it SHOULD use a temporary address to
fetch the PvD Additional Information and MAY deprecate the used
temporary address and generate a new temporary address afterward.

If the HTTP status of the answer is greater than or equal to 400, the
host MUST close its connection and consider that there is no PvD
Additional Information. If the HTTP status of the answer is between
300 and 399, inclusive, it MUST follow the redirection(s). If the
HTTP status of the answer is between 200 and 299, inclusive, the
response is expected to be a single JSON object.

After retrieval of the PvD Additional Information, hosts MUST
remember the last Sequence Number value received in an RA including
the same PvD ID. Whenever a new RA for the same PvD is received with
a different Sequence Number value, or whenever the expiry date for
the additional information is reached, hosts MUST deprecate the
Additional Information and stop using it.

Hosts retrieving a new PvD Additional Information object MUST check
for the presence and validity of the mandatory fields specified in
Section 4.3. A retrieved object including an expiration time that is
already past or missing a mandatory element MUST be ignored.

In order to avoid synchronized queries toward the server hosting the
PvD Additional Information when an object expires, object updates are
delayed by a randomized backoff time.

* When a host performs a JSON object update after it detected a
change in the PvD Option Sequence Number, it MUST add a delay
before sending the query. The target time for the delay is
calculated as a random time between zero and 2^((10 + Delay))
milliseconds, where 'Delay' corresponds to the 4-bit unsigned
integer in the last received PvD Option.

* When a host last retrieved a JSON object at time A that includes
an expiry time B using the "expires" key, and the host is
configured to keep the PvD Additional Information up to date, it
MUST add some randomness into its calculation of the time to fetch
the update. The target time for fetching the updated object is
calculated as a uniformly random time in the interval [(B-A)/2,B].

In the example in Figure 2, the Delay field value is 1; this means
that the host calculates its delay by choosing a uniformly random
time between 0 and 2^((10 + 1)) milliseconds, i.e., between 0 and
2048 milliseconds.

Since the Delay value is directly within the PvD Option rather than
the object itself, an operator may perform a push-based update by
incrementing the Sequence Number value while changing the Delay value
depending on the criticality of the update and the capacity of its
PvD Additional Information servers.

In addition to adding a random delay when fetching Additional
Information, hosts MUST enforce a minimum time between requesting
Additional Information for a given PvD on the same network. This
minimum time is RECOMMENDED to be 10 seconds, in order to avoid hosts
causing a denial-of-service on the PvD server. Hosts also MUST limit
the number of requests that are made to different PvD Additional
Information servers on the same network within a short period of
time. A RECOMMENDED value is to issue no more than five PvD
Additional Information requests in total on a given network within 10
seconds. For more discussion, see Section 6.

The PvD Additional Information object includes a set of IPv6 prefixes
(under the key "prefixes") that MUST be checked against all the
Prefix Information Options advertised in the RA. If any of the
prefixes included in any associated PIO is not covered by at least
one of the listed prefixes, the PvD Additional Information MUST be
considered to be a misconfiguration and MUST NOT be used by the host.
See Section 4.4 for more discussion on handling such
misconfigurations.

If the request for PvD Additional Information fails due to a TLS
certificate validation error, an HTTP error, or because the retrieved
file does not contain valid PvD JSON, hosts MUST close any connection
used to fetch the PvD Additional Information and MUST NOT request the
information for that PvD ID again for the duration of the local
network attachment. If a host detects 10 or more such failures to
fetch PvD Additional Information, the local network is assumed to be
misconfigured or under attack and the host MUST NOT make any further
requests for any PvD Additional Information, belonging to any PvD ID,
for the duration of the local network attachment. For more
discussion, see Section 6.

4.2. Operational Consideration to Providing the PvD Additional
Information

Whenever the H-flag is set in the PvD Option, a valid PvD Additional
Information object MUST be made available to all hosts receiving the
RA by the network operator. In particular, when a captive portal is
present, hosts MUST still be allowed to perform DNS, certificate
validation, and HTTP-over-TLS operations related to the retrieval of
the object, even before logging into the captive portal.

Routers SHOULD increment the PvD Option Sequence Number by one
whenever a new PvD Additional Information object is available and
should be retrieved by hosts. If the value exceeds what can be
stored in the Sequence Number field, it MUST wrap back to zero.

The server providing the JSON files SHOULD also check whether the
client address is contained by the prefixes listed in the Additional
Information and SHOULD return a 403 response code if there is no
match.

4.3. PvD Additional Information Format

The PvD Additional Information is a JSON object.

The following table presents the mandatory keys, which MUST be
included in the object:

+============+===============+===========+========================+
| JSON key | Description | Type | Example |
+============+===============+===========+========================+
| identifier | PvD ID FQDN | String | "pvd.example.com." |
+------------+---------------+-----------+------------------------+
| expires | Date after | [RFC3339] | "2020-05-23T06:00:00Z" |
| | which this | Date | |
| | object is no | | |
| | longer valid | | |
+------------+---------------+-----------+------------------------+
| prefixes | Array of IPv6 | Array of | ["2001:db8:1::/48", |
| | prefixes | strings | "2001:db8:4::/48"] |
| | valid for | | |
| | this PvD | | |
+------------+---------------+-----------+------------------------+

Table 1

A retrieved object that does not include all three of these keys at
the root of the JSON object MUST be ignored. All three keys need to
be validated; otherwise, the object MUST be ignored. The value
stored for "identifier" MUST be matched against the PvD ID FQDN
presented in the PvD Option using the comparison mechanism described
in Section 3.4. The value stored for "expires" MUST be a valid date
in the future. If the PIO of the received RA is not covered by at
least one of the "prefixes" key, the retrieved object SHOULD be
ignored.

The following table presents some optional keys that MAY be included
in the object.

+============+======================+==========+====================+
| JSON key | Description | Type | Example |
+============+======================+==========+====================+
| dnsZones | DNS zones searchable | Array | ["example.com", |
| | and accessible | of | "sub.example.com"] |
| | | strings | |
+------------+----------------------+----------+--------------------+
| noInternet | No Internet; set to | Boolean | true |
| | "true" when the PvD | | |
| | is restricted | | |
+------------+----------------------+----------+--------------------+

Table 2

It is worth noting that the JSON format allows for extensions.
Whenever an unknown key is encountered, it MUST be ignored along with
its associated elements.

Private-use or experimental keys MAY be used in the JSON dictionary.
In order to avoid such keys colliding with the keys registered by
IANA, implementers or vendors defining private-use or experimental
keys MUST create sub-dictionaries. If a set of PvD Additional
Information keys are defined by an organization that has a formal URN
namespace [IANA-URN], the URN namespace SHOULD be used as the top-
level JSON key for the sub-dictionary. For other private uses, the
sub-dictionary key SHOULD follow the format of "vendor-*", where the
"*" is replaced by the implementer's or vendor's identifier. For
example, keys specific to the FooBar organization could use "vendor-
foobar". If a host receives a sub-dictionary with an unknown key,
the host MUST ignore the contents of the sub-dictionary.

4.3.1. Example

The following two examples show how the JSON keys defined in this
document can be used:

{
"identifier": "cafe.example.com.",
"expires": "2020-05-23T06:00:00Z",
"prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
}

{
"identifier": "company.foo.example.com.",
"expires": "2020-05-23T06:00:00Z",
"prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
"vendor-foo":
{
"private-key": "private-value",
},
}

4.4. Detecting Misconfiguration and Misuse

Hosts MUST validate the TLS server certificate when retrieving PvD
Additional Information, as detailed in Section 4.1.

Hosts MUST verify that all prefixes in all the RA PIOs are covered by
a prefix from the PvD Additional Information. An adversarial router
attempting to spoof the definition of an Explicit PvD, without the
ability to modify the PvD Additional Information, would need to
perform IPv6-to-IPv6 Network Prefix Translation (NPTv6) [RFC6296] in
order to circumvent this check. Thus, this check cannot prevent all
spoofing, but it can detect misconfiguration or mismatched routers
that are not adding a NAT.

If NPTv6 is being added in order to spoof PvD ownership, the HTTPS
server for Additional Information can detect this misconfiguration.
The HTTPS server SHOULD validate the source addresses of incoming
connections (see Section 4.1). This check gives reasonable assurance
that NPTv6 was not used and restricts the information to the valid
network users.If the PvD does not provision IPv4 (it does not include
the L-flag in the RA), the server cannot validate the source
addresses of connections using IPv4. Thus, the PvD ID FQDN for such
PvDs SHOULD NOT have a DNS A record.

5. Operational Considerations

This section describes some example use cases of PvDs. For the sake
of simplicity, the RA messages will not be described in the usual
ASCII art but rather in an indented list. Values in the PvD Option
header that are not included in the example are assumed to be zero or
false (such as the H-flag, Sequence Number, and Delay fields).

5.1. Exposing Extra RA Options to PvD-Aware Hosts

In this example, there is one RA message sent by the router. This
message contains some options applicable to all hosts on the network
and also a PvD Option that also contains other options only visible
to PvD-aware hosts.

* RA Header: router lifetime = 6000

* Prefix Information Option: length = 4, prefix = 2001:db8:cafe::/64

* PvD Option header: length = 3 + 5 + 4, PvD ID FQDN = example.org.,
R-flag = 0 (actual length of the header with padding 24 bytes = 3
* 8 bytes)

- Recursive DNS Server: length = 5, addresses =
[2001:db8:cafe::53, 2001:db8:f00d::53]

- Prefix Information Option: length = 4, prefix =
2001:db8:f00d::/64

Note that a PvD-aware host will receive two different prefixes,
"2001:db8:cafe::/64" and "2001:db8:f00d::/64", both associated with
the same PvD (identified by "example.org."). A non-PvD-aware host
will only receive one prefix, "2001:db8:cafe::/64".

5.2. Different RAs for PvD-Aware and Non-PvD-Aware Hosts

It is expected that for some years, networks will have a mixed
environment of PvD-aware hosts and non-PvD-aware hosts. If there is
a need to give specific information to PvD-aware hosts only, then it
is RECOMMENDED to send two RA messages, one for each class of hosts.
This approach allows for two distinct sets of configuration
information to be sent in a way that will not disrupt non-PvD-aware
hosts. It also lowers the risk that a single RA message will
approach its MTU limit due to duplicated information.

If two RA messages are sent for this reason, they MUST be sent from
two different link-local source addresses (Section 3.2). For
example, here is the RA sent for non-PvD-aware hosts:

* RA Header: router lifetime = 6000 (non-PvD-aware hosts will use
this router as a default router)

* Prefix Information Option: length = 4, prefix = 2001:db8:cafe::/64

* Recursive DNS Server Option: length = 3, addresses =
[2001:db8:cafe::53]

* PvD Option header: length = 3 + 2, PvD ID FQDN = foo.example.org.,
R-flag = 1 (actual length of the header 24 bytes = 3 * 8 bytes)

- RA Header: router lifetime = 0 (PvD-aware hosts will not use
this router as a default router), implicit length = 2

And here is the RA sent for PvD-aware hosts:

* RA Header: router lifetime = 0 (non-PvD-aware hosts will not use
this router as a default router)

* PvD Option header: length = 3 + 2 + 4 + 3, PvD ID FQDN =
bar.example.org., R-flag = 1 (actual length of the header 24 bytes
= 3 * 8 bytes)

- RA Header: router lifetime = 1600 (PvD-aware hosts will use
this router as a default router), implicit length = 2

- Prefix Information Option: length = 4, prefix =
2001:db8:f00d::/64

- Recursive DNS Server Option: length = 3, addresses =
[2001:db8:f00d::53]

In the above example, non-PvD-aware hosts will only use the first
listed RA sent by their default router and use the
"2001:db8:cafe::/64" prefix. PvD-aware hosts will autonomously
configure addresses from both PIOs but will only use the source
address in "2001:db8:f00d::/64" to communicate past the first-hop
router since only the router sending the second RA will be used as
the default router; similarly, they will use the DNS server
"2001:db8:f00d::53" when communicating from this address.

5.3. Enabling Multihoming for PvD-Aware Hosts

In this example, the goal is to have one prefix from one RA be usable
by both non-PvD-aware and PvD-aware hosts and to have another prefix
usable only by PvD-aware hosts. This allows PvD-aware hosts to be
able to effectively multihome on the network.

The first RA is usable by all hosts. The only difference for PvD-
aware hosts is that they can explicitly identify the PvD ID
associated with the RA. PvD-aware hosts will also use this prefix to
communicate with non-PvD-aware hosts on the same network.

* RA Header: router lifetime = 6000 (non-PvD-aware hosts will use
this router as a default router)

* Prefix Information Option: length = 4, prefix = 2001:db8:cafe::/64

* Recursive DNS Server Option: length = 3, addresses =
[2001:db8:cafe::53]

* PvD Option header: length = 3, PvD ID FQDN = foo.example.org.,
R-flag = 0 (actual length of the header 24 bytes = 3 * 8 bytes)

The second RA contains a prefix usable only by PvD-aware hosts. Non-
PvD-aware hosts will ignore this RA; hence, only the PvD-aware hosts
will be multihomed.

* RA Header: router lifetime = 0 (non-PvD-aware hosts will not use
this router as a default router)

* PvD Option header: length = 3 + 2 + 4 + 3, PvD ID FQDN =
bar.example.org., R-flag = 1 (actual length of the header 24 bytes
= 3 * 8 bytes)

- RA Header: router lifetime = 1600 (PvD-aware hosts will use
this router as a default router), implicit length = 2

- Prefix Information Option: length = 4, prefix =
2001:db8:f00d::/64

- Recursive DNS Server Option: length = 3, addresses =
[2001:db8:f00d::53]

Note: the above examples assume that the router has received its PvD
IDs from upstream routers or via some other configuration mechanism.
Another document could define ways for the router to generate its own
PvD IDs to allow the above scenario in the absence of PvD ID
provisioning.

5.4. Providing Additional Information to PvD-Aware Hosts

In this example, the router indicates that it provides Additional
Information using the H-flag. The Sequence Number on the PvD Option
is set to 7 in this example.

* RA Header: router lifetime = 6000

* Prefix Information Option: length = 4, prefix = 2001:db8:cafe::/64

* Recursive DNS Server Option: length = 3, addresses =
[2001:db8:cafe::53]

* PvD Option header: length = 3, PvD ID FQDN = cafe.example.com.,
Sequence Number = 7, R-flag = 0, H-flag = 1 (actual length of the
header with padding 24 bytes = 3 * 8 bytes)

A PvD-aware host will fetch <https://cafe.example.com/.well-known/
pvd> to get the additional information. The following example shows
a GET request that the host sends, in HTTP/2 syntax [RFC7540]:

:method = GET
:scheme = https
:authority = cafe.example.com
:path = /.well-known/pvd
accept = application/pvd+json

The HTTP server will respond with the JSON Additional Information:

:status = 200
content-type = application/pvd+json
content-length = 116

{
"identifier": "cafe.example.com.",
"expires": "2020-05-23T06:00:00Z",
"prefixes": ["2001:db8:cafe::/48"],
}

At this point, the host has the PvD Additional Information and knows
the expiry time. When either the expiry time passes or a new
Sequence Number is provided in an RA, the host will re-fetch the
Additional Information.

For example, if the router sends a new RA with the Sequence Number
set to 8, the host will re-fetch the Additional Information:

* PvD Option header: length = 3 + 5 + 4 , PvD ID FQDN =
cafe.example.com., Sequence Number = 8, R-flag = 0, H-flag = 1
(actual length of the header with padding 24 bytes = 3 * 8 bytes)

However, if the router sends a new RA, but the Sequence Number has
not changed, the host would not re-fetch the Additional Information
(until and unless the expiry time of the Additional Information has
passed).

6. Security Considerations

Since the PvD Option can contain an RA header and other RA options,
any security considerations that apply for specific RA options
continue to apply when used within a PvD Option.

Although some solutions such as IPsec or SEcure Neighbor Discovery
(SeND) [RFC3971] can be used in order to secure the IPv6 Neighbor
Discovery Protocol, in practice, actual deployments largely rely on
link-layer or physical-layer security mechanisms (e.g., 802.1x
[IEEE8021X]) in conjunction with RA-Guard [RFC6105].

If multiple RAs are sent for a single PvD to avoid fragmentation,
dropping packets can lead to processing only part of a PvD Option,
which could lead to hosts receiving only part of the contained
options. As discussed in Section 3.2, routers MUST include the PvD
Option in all fragments generated.

This specification does not improve the Neighbor Discovery Protocol
security model but simply validates that the owner of the PvD FQDN
authorizes its use with the prefix advertised by the router. In
combination with implicit trust in the local router (if present),
this gives the host some level of assurance that the PvD is
authorized for use in this environment. However, when the local
router cannot be trusted, no such guarantee is available.

It must be noted that Section 4.4 of this document only provides
reasonable assurance against misconfiguration but does not prevent a
hostile network access provider from advertising incorrect
information that could lead applications or hosts to select a hostile
PvD. However, a host that correctly implements the multiple PvD
architecture [RFC7556] using the mechanism described in this document
will be less susceptible to some attacks than a host that does not by
being able to check for the various misconfigurations or
inconsistencies described in this document.

Since expiration times provided in PvD Additional Information use
absolute time, these values can be skewed due to clock skew or for
hosts without an accurate time base. Such time values MUST NOT be
used for security-sensitive functionality or decisions.

An attacker generating RAs on a local network can use the H-flag and
the PvD ID to cause hosts on the network to make requests for PvD
Additional Information from servers. This can become a denial-of-
service attack, in which an attacker can amplify its attack by
triggering TLS connections to arbitrary servers in response to
sending UDP packets containing RA messages. To mitigate this attack,
hosts MUST:

* limit the rate at which they fetch a particular PvD's Additional
Information;

* limit the rate at which they fetch any PvD Additional Information
on a given local network;

* stop making requests for a PvD ID that does not respond with valid
JSON; and

* stop making requests for all PvD IDs once a certain number of
failures is reached on a particular network.

Details are provided in Section 4.1. This attack can be targeted at
generic web servers, in which case the host behavior of stopping
requesting for any server that doesn't behave like a PvD Additional
Information server is critical. Limiting requests for a specific PvD
ID might not be sufficient if the attacker changes the PvD ID values
quickly, so hosts also need to stop requesting if they detect
consistent failure when on a network that is under attack. For cases
in which an attacker is pointing hosts at a valid PvD Additional
Information server (but one that is not actually associated with the
local network), the server SHOULD reject any requests that do not
originate from the expected IPv6 prefix as described in Section 4.2.

7. Privacy Considerations

Retrieval of the PvD Additional Information over HTTPS requires early
communications between the connecting host and a server that may be
located further than the first-hop router. Although this server is
likely to be located within the same administrative domain as the
default router, this property can't be ensured. To minimize the
leakage of identity information while retrieving the PvD Additional
Information, hosts SHOULD make use of an IPv6 temporary address and
SHOULD NOT include any privacy-sensitive data, such as a User-Agent
header field or an HTTP cookie.

Hosts might not always fetch PvD Additional Information, depending on
whether or not they expect to use the information. However, if a
host allows requesting Additional Information for certain PvD IDs, an
attacker could send various PvD IDs in RAs to detect which PvD IDs
are allowed by the client. To avoid this, hosts SHOULD either fetch
Additional Information for all eligible PvD IDs on a given local
network or fetch the information for none of them.

From a user privacy perspective, retrieving the PvD Additional
Information is not different from establishing a first connection to
a remote server or even performing a single DNS lookup. For example,
most operating systems already perform early queries to static web
sites, such as <http://captive.example.com/hotspot-detect.html>, in
order to detect the presence of a captive portal.

The DNS queries associated with the PvD Additional Information MUST
use the DNS servers indicated by the associated PvD, as described in
Section 4.1. This ensures the name of the PvD Additional Information
server is not unintentionally sent on another network, thus leaking
identifying information about the networks with which the client is
associated.

There may be some cases where hosts, for privacy reasons, should
refrain from accessing servers that are located outside a certain
network boundary. In practice, this could be implemented as an
allowed list of 'trusted' FQDNs and/or IP prefixes that the host is
allowed to communicate with. In such scenarios, the host SHOULD
check that the provided PvD ID, as well as the IP address that it
resolves into, are part of the allowed list.

Network operators SHOULD restrict access to PvD Additional
Information to only expose it to hosts that are connected to the
local network, especially if the Additional Information would provide
information about local network configuration to attackers. This can
be implemented by allowing access from the addresses and prefixes
that the router provides for the PvD, which will match the prefixes
contained in the PvD Additional Information. This technique is
described in Section 4.2.

8. IANA Considerations

8.1. Change to IPv6 Neighbor Discovery Option Formats Registry

IANA has removed the 'reclaimable' tag for value 21 for the PvD
Option in the "IPv6 Neighbor Discovery Option Formats" registry.

8.2. New Entry in the Well-Known URIs Registry

IANA has added a new entry in the "Well-Known URIs" registry
[RFC8615] with the following information:

URI suffix: pvd

Change controller: IETF

Specification document: RFC 8801

Status: permanent

Related information: N/A

8.3. New Additional Information PvD Keys Registry

IANA has created and will maintain a new registry called "Additional
Information PvD Keys", which reserves JSON keys for use in PvD
Additional Information. The initial contents of this registry are
given in Section 4.3 (both the table of mandatory keys and the table
of optional keys).

The status of a key as mandatory or optional is intentionally not
denoted in the table to allow for flexibility in future use cases.
Any new assignments of keys will be considered as optional for the
purpose of the mechanism described in this document.

New assignments in the "Additional Information PvD Keys" registry
will be administered by IANA through Expert Review [RFC8126].
Experts are requested to ensure that defined keys do not overlap in
names or semantics and that they represent non-vendor-specific use
cases. Vendor-specific keys SHOULD use sub-dictionaries, as
described in Section 4.3.

IANA has placed the "Additional Information PvD Keys" registry within
a new registry entitled "Provisioning Domains (PvDs)".

8.4. New PvD Option Flags Registry

IANA has also created and will maintain a new registry entitled "PvD
Option Flags". This new registry reserves bit positions from 0 to 11
to be used in the PvD Option bitmask. This document assigns bit
positions 0, 1, and 2 as shown in the table below. Future
assignments require Standards Action [RFC8126].

+======+============+===========+
| Bit | Name | Reference |
+======+============+===========+
| 0 | H-flag | RFC 8801 |
+------+------------+-----------+
| 1 | L-flag | RFC 8801 |
+------+------------+-----------+
| 2 | R-flag | RFC 8801 |
+------+------------+-----------+
| 3-11 | Unassigned | |
+------+------------+-----------+

Table 3

Since these flags apply to an IPv6 Router Advertisement Option, IANA
has placed this registry under the existing "Internet Control Message
Protocol version 6 (ICMPv6) Parameters" registry and provided a link
on the new "Provisioning Domains (PvDs)" registry.

8.5. PvD JSON Media Type Registration

This document registers the media type for PvD JSON text,
"application/pvd+json".

Type name: application

Subtype name: pvd+json

Required parameters: N/A

Optional parameters: N/A

Encoding considerations: Encoding considerations are identical to
those specified for the "application/json" media type.

Security considerations: See Section 6 of RFC 8801.

Interoperability considerations: This document specifies the format
of conforming messages and the interpretation thereof.

Published specification: RFC 8801

Applications that use this media type: This media type is intended
to be used by networks advertising additional Provisioning Domain
information and clients looking up such information.

Fragment identifier considerations: N/A

Additional information: N/A

Person & email address to contact for further information: See
Authors' Addresses section

Intended usage: COMMON

Restrictions on usage: N/A

Author: IETF

Change controller: IETF

9. References

9.1. Normative References

[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.

[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>.

[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.

[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<https://www.rfc-editor.org/info/rfc3339>.

[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>.

[RFC4343] Eastlake 3rd, D., "Domain Name System (DNS) Case
Insensitivity Clarification", RFC 4343,
DOI 10.17487/RFC4343, January 2006,
<https://www.rfc-editor.org/info/rfc4343>.

[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>.

[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<https://www.rfc-editor.org/info/rfc4941>.

[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>.

[RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
with IPv6 Neighbor Discovery", RFC 6980,
DOI 10.17487/RFC6980, August 2013,
<https://www.rfc-editor.org/info/rfc6980>.

[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<https://www.rfc-editor.org/info/rfc7493>.

[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>.

[RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain
Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
<https://www.rfc-editor.org/info/rfc7556>.

[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>.

[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>.

[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.

[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/info/rfc8615>.

9.2. Informative References

[IANA-URN] IANA, "Uniform Resource Names (URN) Namespaces",
<https://www.iana.org/assignments/urn-namespaces/>.

[IEEE8021X]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks -- Port-Based Network Access Control", IEEE
802.1X-2020, DOI 10.1109/IEEESTD.2020.9018454,
<https://ieeexplore.ieee.org/document/9018454>.

[MPVD-API] Kline, E., "Multiple Provisioning Domains API
Requirements", Work in Progress, Internet-Draft, draft-
kline-mif-mpvd-api-reqs-00, 1 November 2015,
<https://tools.ietf.org/html/draft-kline-mif-mpvd-api-
reqs-00>.

[MPVD-DNS] Stenberg, M. and S. Barth, "Multiple Provisioning Domains
using Domain Name System", Work in Progress, Internet-
Draft, draft-stenberg-mif-mpvd-dns-00, 15 October 2015,
<https://tools.ietf.org/html/draft-stenberg-mif-mpvd-dns-
00>.

[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.

[RFC3646] Droms, R., Ed., "DNS Configuration options for Dynamic
Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
DOI 10.17487/RFC3646, December 2003,
<https://www.rfc-editor.org/info/rfc3646>.

[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.

[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <https://www.rfc-editor.org/info/rfc4389>.

[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
DOI 10.17487/RFC6105, February 2011,
<https://www.rfc-editor.org/info/rfc6105>.

[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.

[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.

[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
DOI 10.17487/RFC6147, April 2011,
<https://www.rfc-editor.org/info/rfc6147>.

[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, DOI 10.17487/RFC6296, June 2011,
<https://www.rfc-editor.org/info/rfc6296>.

[RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A.,
Galperin, S., and C. Adams, "X.509 Internet Public Key
Infrastructure Online Certificate Status Protocol - OCSP",
RFC 6960, DOI 10.17487/RFC6960, June 2013,
<https://www.rfc-editor.org/info/rfc6960>.

[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.

[RFC7278] Byrne, C., Drown, D., and A. Vizdal, "Extending an IPv6
/64 Prefix from a Third Generation Partnership Project
(3GPP) Mobile Interface to a LAN Link", RFC 7278,
DOI 10.17487/RFC7278, June 2014,
<https://www.rfc-editor.org/info/rfc7278>.

[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.

[RFC8106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Options for DNS Configuration",
RFC 8106, DOI 10.17487/RFC8106, March 2017,
<https://www.rfc-editor.org/info/rfc8106>.

[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.

Acknowledgments

Many thanks to Markus Stenberg and Steven Barth for their earlier
work on [MPVD-DNS], as well as to Basile Bruneau, who was author of
an early draft version of this document.

Thanks also to Marcus Keane, Mikael Abrahamsson, Ray Bellis, Zhen
Cao, Tim Chown, Lorenzo Colitti, Michael Di Bartolomeo, Ian Farrer,
Phillip Hallam-Baker, Bob Hinden, Tatuya Jinmei, Erik Kline, Ted
Lemon, Paul Hoffman, Dave Thaler, Suresh Krishnan, Gorry Fairhurst,
Jen Lenkova, Veronika McKillop, Mark Townsley, and James Woodyatt for
useful and interesting discussions and reviews.

Finally, special thanks to Thierry Danis for his valuable input and
implementation efforts, Tom Jones for his integration effort into the
NEAT project, and Rigil Salim for his implementation work.

Authors' Addresses

Pierre Pfister
Cisco
11 Rue Camille Desmoulins
92130 Issy-les-Moulineaux
France

Email: [email protected]

Éric Vyncke
Cisco
De Kleetlaan, 6
1831 Diegem
Belgium

Email: [email protected]

Tommy Pauly
Apple Inc.
One Apple Park Way
Cupertino, California 95014
United States of America

Email: [email protected]

David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain
View, California 94043
United States of America

Email: [email protected]

Wenqin Shao
Cisco
11 Rue Camille Desmoulins
92130 Issy-les-Moulineaux
France

Email: [email protected]