Internet Engineering Task Force (IETF) Y. Wei, Ed.

Internet Engineering Task Force (IETF) Y. Wei, Ed.
Request for Comments: 9263 ZTE Corporation
Category: Standards Track U. Elzur
ISSN: 2070-1721 Intel
S. Majee
Individual Contributor
C. Pignataro
Cisco
D. Eastlake 3rd
Futurewei Technologies
August 2022

Network Service Header (NSH) Metadata Type 2 Variable-Length Context
Headers

Abstract

Service Function Chaining (SFC) uses the Network Service Header (NSH)
(RFC 8300) to steer and provide context metadata (MD) with each
packet. Such metadata can be of various types, including MD Type 2,
consisting of Variable-Length Context Headers. This document
specifies several such Context Headers that can be used within a
Service Function Path (SFP).

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/rfc9263.

Copyright Notice

Copyright (c) 2022 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
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(https://trustee.ietf.org/license-info) in effect on the date of
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in the Revised BSD License.

Table of Contents

1. Introduction
2. Conventions Used in This Document
2.1. Terminology
2.2. Requirements Language
3. NSH MD Type 2 Format
4. NSH MD Type 2 Context Headers
4.1. Forwarding Context
4.2. Tenant ID
4.3. Ingress Network Node Information
4.4. Ingress Network Source Interface
4.5. Flow ID
4.6. Source and/or Destination Groups
4.7. Policy ID
5. Security Considerations
5.1. Forwarding Context
5.2. Tenant ID
5.3. Ingress Network Node Information
5.4. Ingress Node Source Interface
5.5. Flow ID
5.6. Source and/or Destination Groups
5.7. Policy ID
6. IANA Considerations
6.1. MD Type 2 Context Types
6.2. Forwarding Context Types
6.3. Flow ID Context Types
7. References
7.1. Normative References
7.2. Informative References
Acknowledgments
Authors' Addresses

1. Introduction

The Network Service Header (NSH) [RFC8300] is the Service Function
Chaining (SFC) encapsulation that supports the SFC architecture
[RFC7665]. As such, the NSH provides the following key elements:

1. Service Function Path (SFP) identification

2. indication of location within an SFP

3. optional, per-packet metadata (fixed-length or variable-length)

[RFC8300] further defines two metadata formats (MD Types): 1 and 2.
MD Type 1 defines the fixed-length, 16-octet metadata, whereas MD
Type 2 defines a variable-length context format for metadata. This
document defines several common metadata Context Headers for use
within NSH MD Type 2. These supplement the Subscriber Identifier and
Performance Policy MD Type 2 metadata Context Headers specified in
[RFC8979].

This document does not address metadata usage, updating/chaining of
metadata, or other SFP functions. Those topics are described in
[RFC8300].

2. Conventions Used in This Document

2.1. Terminology

This document uses the terminology defined in the SFC architecture
[RFC7665] and the NSH [RFC8300].

2.2. Requirements Language

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. NSH MD Type 2 Format

An NSH is composed of a 4-octet Base Header, a 4-octet Service Path
Header, and optional Context Headers. The Base Header identifies the
MD Type in use:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|O|U| TTL | Length |U|U|U|U|MD Type| Next Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: NSH Base Header

Please refer to the NSH [RFC8300] for a detailed header description.

When the Base Header specifies MD Type = 0x2, zero or more Variable-
Length Context Headers MAY be added, immediately following the
Service Path Header. Figure 2 below depicts the format of the
Context Header as defined in Section 2.5.1 of [RFC8300].

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class | Type |U| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable-Length Metadata |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: NSH Variable-Length Context Headers

4. NSH MD Type 2 Context Headers

[RFC8300] specifies Metadata Class 0x0000 as IETF Base NSH MD Class.
In this document, metadata types are defined for the IETF Base NSH MD
Class. The Context Headers specified in the subsections below are as
follows:

1. Forwarding Context

2. Tenant ID

3. Ingress Network Node Information

4. Ingress Node Source Interface

5. Flow ID

6. Source and/or Destination Groups

7. Policy ID

4.1. Forwarding Context

This metadata context carries a network forwarding context, used for
segregation and forwarding scope. Forwarding context can take
several forms depending on the network environment, for example,
Virtual eXtensible Local Area Network (VXLAN) / Generic Protocol
Extension for VXLAN (VXLAN-GPE) Virtual Network Identifier (VNID),
VPN Routing and Forwarding (VRF) identification, or VLAN.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x04 |U| Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|CT=0x0 | Reserved | VLAN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: VLAN Forwarding Context

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x04 |U| Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|CT=0x1 |Resv | Service VLAN ID | Customer VLAN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: QinQ Forwarding Context

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x04 |U| Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|CT=0x2 | Reserved | MPLS VPN Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 5: MPLS VPN Forwarding Context

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x04 |U| Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|CT=0x3 | Resv | Virtual Network Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 6: VNI Forwarding Context

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x04 |U| Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|CT=0x4 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 7: Session ID Forwarding Context

The fields are described as follows:

Context Type (CT): This 4-bit field that defines the interpretation
of the Forwarding Context field. Please see the IANA
considerations in Section 6.2. This document defines these CT
values:

0x0: 12-bit VLAN identifier [IEEE.802.1Q_2018]. See Figure 3.

0x1: 24-bit double tagging identifiers. A service VLAN tag
followed by a customer VLAN tag [IEEE.802.1Q_2018]. The two
VLAN IDs are concatenated and appear in the same order that
they appeared in the payload. See Figure 4.

0x2: 20-bit MPLS VPN label [RFC3032] [RFC4364]. See Figure 5.

0x3: 24-bit virtual network identifier (VNI) [RFC8926]. See
Figure 6.

0x4: 32-bit Session ID [RFC3931]. This is called Key in GRE
[RFC2890]. See Figure 7.

Reserved (Resv): These bits in the context fields MUST be sent as
zero and ignored on receipt.

4.2. Tenant ID

Tenant identification is often used for segregation within a multi-
tenant environment. Orchestration system-generated Tenant IDs are an
example of such data. This Context Header carries the value of the
Tenant ID. Virtual Tenant Network (VTN) [OpenDaylight-VTN] is an
application that provides multi-tenant virtual networks on a
Software-Defined Networking (SDN) controller.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x05 |U| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Tenant ID ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 8: Tenant ID List

The fields are described as follows:

Length: Indicates the length of the Tenant ID in octets (see
Section 2.5.1 of [RFC8300]).

Tenant ID: Represents an opaque value pointing to orchestration
system-generated Tenant ID. The structure and semantics of this
field are specific to the operator's deployment across its
operational domain and are specified and assigned by an
orchestration function. The specifics of that orchestration-based
assignment are outside the scope of this document.

4.3. Ingress Network Node Information

This Context Header carries a Node ID of the network node at which
the packet entered the SFC-enabled domain. This node will
necessarily be a classifier [RFC7665]. In cases where the Service
Path Identifier (SPI) identifies the ingress node, this Context
Header is superfluous.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x06 |U| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Node ID ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 9: Ingress Network Node ID

The fields are described as follows:

Length: Indicates the length of the Node ID in octets (see
Section 2.5.1 of [RFC8300]).

Node ID: Represents an opaque value of the ingress network Node ID.
The structure and semantics of this field are deployment specific.
For example, Node ID may be a 4-octet IPv4 address Node ID, a
16-octet IPv6 address Node ID, a 6-octet MAC address, an 8-octet
MAC address (64-bit Extended Unique Identifier (EUI-64)), etc.

4.4. Ingress Network Source Interface

This context identifies the ingress interface of the ingress network
node. The l2vlan (135), l3ipvlan (136), ipForward (142), and mpls
(166) in [IANAifType] are examples of source interfaces.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x07 |U| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Source Interface ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 10: Ingress Network Source Interface

The fields are described as follows:

Length: Indicates the length of the Source Interface in octets (see
Section 2.5.1 of [RFC8300]).

Source Interface: Represents an opaque value of the identifier of
the ingress interface of the ingress network node.

4.5. Flow ID

Flow ID provides a field in NSH MD Type 2 to label packets belonging
to the same flow. For example, [RFC8200] defines IPv6 Flow Label as
Flow ID. Another example of Flow ID is how [RFC6790] defines an
entropy label that is generated based on flow information in the MPLS
network. Absence of this field or a value of zero denotes that
packets have not been labeled with a Flow ID.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x08 |U| Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|CT=0x0 | Reserved | IPv6 Flow ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 11: IPv6 Flow ID

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x08 |U| Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|CT=0x1 | Reserved | MPLS entropy label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 12: MPLS Entropy Label

The fields are described as follows:

Length: Indicates the length of the Flow ID in octets (see
Section 2.5.1 of [RFC8300]). For example, the IPv6 Flow Label in
[RFC8200] is 20 bits long. An entropy label in the MPLS network
in [RFC6790] is also 20 bits long.

Context Type (CT): This 4-bit field that defines the interpretation
of the Flow ID field. Please see the IANA considerations in
Section 6.3. This document defines these CT values:

0x0: 20-bit IPv6 Flow Label in [RFC8200]. See Figure 11.

0x1: 20-bit entropy label in the MPLS network in [RFC6790]. See
Figure 12.

Reserved: These bits in the context fields MUST be sent as zero and
ignored on receipt.

4.6. Source and/or Destination Groups

Intent-based systems can use this data to express the logical
grouping of source and/or destination objects. [OpenStack] and
[OpenDaylight] provide examples of such a system. Each is expressed
as a 32-bit opaque object.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x09 |U| Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Group |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Group |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 13: Source/Destination Groups

If there is no group information specified for the Source Group or
Destination Group field, the field MUST be sent as zero and ignored
on receipt.

4.7. Policy ID

Traffic handling policies are often referred to by a system-generated
identifier, which is then used by the devices to look up the policy's
content locally. For example, this identifier could be an index to
an array, a lookup key, or a database ID. The identifier allows
enforcement agents or services to look up the content of their part
of the policy.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metadata Class = 0x0000 | Type = 0x0A |U| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Policy ID ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 14: Policy ID

The fields are described as follows:

Length: Indicates the length of the Policy ID in octets (see
Section 2.5.1 of [RFC8300]).

Policy ID: Represents an opaque value of the Policy ID.

This Policy ID is a general Policy ID, essentially a key to allow
Service Functions (SFs) to know which policies to apply to packets.
Those policies generally will not have much to do with performance
but rather with what specific treatment to apply. It may, for
example, select a URL filter data set for a URL filter or select a
video transcoding policy in a transcoding SF. The Performance Policy
ID in [RFC8979] is described there as having very specific use and,
for example, says that fully controlled SFPs would not use it. The
Policy ID in this document is for cases not covered by [RFC8979].

5. Security Considerations

A misbehaving node from within the SFC-enabled domain may alter the
content of the Context Headers, which may lead to service disruption.
Such an attack is not unique to the Context Headers defined in this
document. Measures discussed in Section 8 of [RFC8300] describes the
general security considerations for protecting the NSH. [RFC9145]
specifies methods of protecting the integrity of the NSH metadata.
If the NSH includes the Message Authentication Code (MAC) and
Encrypted Metadata Context Header [RFC9145], the authentication of
the packet MUST be verified before using any data. If the
verification fails, the receiver MUST stop processing the Variable-
Length Context Headers and notify an operator.

The security and privacy considerations for the 7 types of Context
Headers specified above are discussed below. Since NSH-ignorant SFs
will never see the NSH, then even if they are malign, they cannot
compromise security or privacy based on the NSH or any of these
Context Headers; however, they could cause compromise based on the
rest of the packet. To the extent that any of these headers are
included when they would be unneeded or have no effect, they provide
a covert channel for the entity adding the Context Header to
communicate a limited amount of arbitrary information to downstream
entities within the SFC-enabled domain.

5.1. Forwarding Context

All of the Forwarding Context variants specified in this document
(those with CT values between 0 and 4) merely repeat a field that is
available in the packet encapsulated by the NSH. These variants
repeat that field in the NSH for convenience. Thus, there are no
special security or privacy considerations in these cases. Any
future new values of CT for the Forwarding Context must specify the
security and privacy considerations for those extensions.

5.2. Tenant ID

The Tenant ID indicates the tenant to which traffic belongs and might
be used to tie together and correlate packets for a tenant that some
monitoring function could not otherwise group, especially if other
possible identifiers were being randomized. As such, it may reduce
security by facilitating traffic analysis but only within the SFC-
enabled domain where this Context Header is present in packets.

5.3. Ingress Network Node Information

The SFC-enabled domain manager normally operates the initial ingress/
classifier node and is thus potentially aware of the information
provided by this Context Header. Furthermore, in many cases, the SPI
that will be present in the NSH identifies or closely constrains the
ingress node. Also, in most cases, it is anticipated that many
entities will be sending packets into an SFC-enabled domain through
the same ingress node. Thus, under most circumstances, this Context
Header is expected to weaken security and privacy to only a minor
extent and only within the SFC-enabled domain.

5.4. Ingress Node Source Interface

This Context Header is likely to be meaningless unless the Ingress
Network Node Information Context Header is also present. When that
node information header is present, this source interface header
provides a more fine-grained view of the source by identifying not
just the initial ingress/classifier node but also the port of that
node on which the data arrived. Thus, it is more likely to identify
a specific source entity or at least to more tightly constrain the
set of possible source entities than just the node information
header. As a result, inclusion of this Context Header with the node
information Context Header is potentially a greater threat to
security and privacy than the node information header alone, but this
threat is still constrained to the SFC-enabled domain.

5.5. Flow ID

The variations of this Context Header specified in this document
simply repeat fields already available in the packet and thus have no
special security or privacy considerations. Any future new values of
CT for the Flow ID must specify the security and privacy
considerations for those extensions.

5.6. Source and/or Destination Groups

This Context Header provides additional information that might help
identify the source and/or destination of packets. Depending on the
granularity of the groups, it could either (1) distinguish packets as
part of flows from and/or to objects where those flows could not
otherwise be easily distinguished but appear to be part of one or
fewer flows or (2) group packet flows that are from and/or to an
object where those flows could not otherwise be easily grouped for
analysis or another purpose. Thus, the presence of this Context
Header with non-zero source and/or destination groups can, within the
SFC-enabled domain, erode security and privacy to an extent that
depends on the details of the grouping.

5.7. Policy ID

This Context Header carries an identifier that nodes in the SFC-
enabled domain can use to look up policy to potentially influence
their actions with regard to the packet carrying this header. If
there are no such decisions regarding their actions, then the header
should not be included. If there are such decisions, the information
on which they are to be based needs to be included somewhere in the
packet. There is no reason for inclusion in this Context Header to
have any security or privacy considerations that would not apply to
any other plaintext way of including such information. It may
provide additional information to help identify a flow of data for
analysis.

6. IANA Considerations

6.1. MD Type 2 Context Types

IANA has assigned the following types (Table 1) from the "NSH IETF-
Assigned Optional Variable-Length Metadata Types" registry available
at [IANA-NSH-MD2].

+=======+==================================+===========+
| Value | Description | Reference |
+=======+==================================+===========+
| 0x04 | Forwarding Context | RFC 9263 |
+-------+----------------------------------+-----------+
| 0x05 | Tenant ID | RFC 9263 |
+-------+----------------------------------+-----------+
| 0x06 | Ingress Network Node ID | RFC 9263 |
+-------+----------------------------------+-----------+
| 0x07 | Ingress Network Interface | RFC 9263 |
+-------+----------------------------------+-----------+
| 0x08 | Flow ID | RFC 9263 |
+-------+----------------------------------+-----------+
| 0x09 | Source and/or Destination Groups | RFC 9263 |
+-------+----------------------------------+-----------+
| 0x0A | Policy ID | RFC 9263 |
+-------+----------------------------------+-----------+

Table 1: Type Values

6.2. Forwarding Context Types

IANA has created a new subregistry for "Forwarding Context Types" at
[IANA-NSH-MD2] as follows.

The registration policy is IETF Review.

+=========+=========================================+===========+
| Value | Description | Reference |
+=========+=========================================+===========+
| 0x0 | 12-bit VLAN identifier | RFC 9263 |
+---------+-----------------------------------------+-----------+
| 0x1 | 24-bit double tagging identifiers | RFC 9263 |
+---------+-----------------------------------------+-----------+
| 0x2 | 20-bit MPLS VPN label | RFC 9263 |
+---------+-----------------------------------------+-----------+
| 0x3 | 24-bit virtual network identifier (VNI) | RFC 9263 |
+---------+-----------------------------------------+-----------+
| 0x4 | 32-bit Session ID | RFC 9263 |
+---------+-----------------------------------------+-----------+
| 0x5-0xE | Unassigned | |
+---------+-----------------------------------------+-----------+
| 0xF | Reserved | RFC 9263 |
+---------+-----------------------------------------+-----------+

Table 2: Forwarding Context Types

6.3. Flow ID Context Types

IANA has created a new subregistry for "Flow ID Context Types" at
[IANA-NSH-MD2] as follows.

The registration policy is IETF Review.

+=========+==========================================+===========+
| Value | Description | Reference |
+=========+==========================================+===========+
| 0x0 | 20-bit IPv6 Flow Label | RFC 9263 |
+---------+------------------------------------------+-----------+
| 0x1 | 20-bit entropy label in the MPLS network | RFC 9263 |
+---------+------------------------------------------+-----------+
| 0x2-0xE | Unassigned | |
+---------+------------------------------------------+-----------+
| 0xF | Reserved | RFC 9263 |
+---------+------------------------------------------+-----------+

Table 3: Flow ID Context Types

7. References

7.1. Normative References

[IANA-NSH-MD2]
IANA, "Network Service Header (NSH) Parameters",
<https://www.iana.org/assignments/nsh>.

[IEEE.802.1Q_2018]
IEEE, "IEEE Standard for Local and Metropolitan Area
Network -- Bridges and Bridged Networks", July 2018,
<https://ieeexplore.ieee.org/document/8403927>.

[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>.

[RFC3931] Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
"Layer Two Tunneling Protocol - Version 3 (L2TPv3)",
RFC 3931, DOI 10.17487/RFC3931, March 2005,
<https://www.rfc-editor.org/info/rfc3931>.

[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>.

[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.

[RFC9145] Boucadair, M., Reddy.K, T., and D. Wing, "Integrity
Protection for the Network Service Header (NSH) and
Encryption of Sensitive Context Headers", RFC 9145,
DOI 10.17487/RFC9145, December 2021,
<https://www.rfc-editor.org/info/rfc9145>.

7.2. Informative References

[IANAifType]
IANA, "IANAifType-MIB DEFINITIONS", 2021,
<https://www.iana.org/assignments/ianaiftype-mib>.

[OpenDaylight]
OpenDaylight, "Group Based Policy User Guide", 2021,
<https://docs.opendaylight.org/en/stable-fluorine/user-
guide/group-based-policy-user-
guide.html?highlight=group%20policy#>.

[OpenDaylight-VTN]
OpenDaylight, "OpenDaylight VTN", 2021, <https://nexus.ope
ndaylight.org/content/sites/site/org.opendaylight.docs/mas
ter/userguide/manuals/userguide/bk-user-guide/
content/_vtn.html>.

[OpenStack]
OpenStack, "GroupBasedPolicy", 2021,
<https://wiki.openstack.org/wiki/GroupBasedPolicy>.

[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
RFC 2890, DOI 10.17487/RFC2890, September 2000,
<https://www.rfc-editor.org/info/rfc2890>.

[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.

[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>.

[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.

[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.

[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.

[RFC8926] Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
"Geneve: Generic Network Virtualization Encapsulation",
RFC 8926, DOI 10.17487/RFC8926, November 2020,
<https://www.rfc-editor.org/info/rfc8926>.

[RFC8979] Sarikaya, B., von Hugo, D., and M. Boucadair, "Subscriber
and Performance Policy Identifier Context Headers in the
Network Service Header (NSH)", RFC 8979,
DOI 10.17487/RFC8979, February 2021,
<https://www.rfc-editor.org/info/rfc8979>.

Acknowledgments

The authors would like to thank Paul Quinn, Behcet Sarikaya, Dirk von
Hugo, Mohamed Boucadair, Gregory Mirsky, and Joel Halpern for
providing invaluable concepts and content for this document.

Authors' Addresses

Yuehua Wei (editor)
ZTE Corporation
No.50, Software Avenue
Nanjing
210012
China
Email: [email protected]

Uri Elzur
Intel
Email: [email protected]

Sumandra Majee
Individual Contributor
Email: [email protected]

Carlos Pignataro
Cisco
Email: [email protected]

Donald E. Eastlake, 3rd
Futurewei Technologies
2386 Panoramic Circle
Apopka, FL 32703
United States of America
Phone: +1-508-333-2270
Email: [email protected]