SRv6 Context Indicator SIDs for SR-Aware Services
draft-lin-spring-srv6-aware-context-indicator-08
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Jiaming Ye , Changwang Lin , Dongjie Lu , Meiling Chen | ||
| Last updated | 2026-07-06 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
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draft-lin-spring-srv6-aware-context-indicator-08
SPRING Working Group J. Ye
Internet Draft China Mobile
Intended status: Standards Track C. Lin
Expires: January 07, 2024 New H3C Technologies
D. Lu
M. Chen
China Mobile
July 6, 2026
SRv6 Context Indicator SIDs for SR-Aware Services
draft-lin-spring-srv6-aware-context-indicator-08
Abstract
A context indicator provides the context on how to process the
packet for service nodes. This document describes how to use SRv6
SIDs as context indicator for SR-aware services. The corresponding
Endpoint behaviors are defined.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 07, 2024.
Copyright Notice
Copyright (c) 2026 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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document must include Revised BSD License text as described in
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Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Revised BSD License.
Table of Contents
1. Introduction...................................................2
2. Use Case.......................................................3
3. SRv6 Context Indicator SIDs....................................5
3.1. End.AN.CI.S: SR-Aware Service Static Context Indicator....5
3.2. End.AN.CI.D: SR-Aware Service Dynamic Context Indicator...6
3.2.1. End.AN.CI.D.A: SR-Aware Service Dynamic Context
Indicator with Variable Context Information in Arguments....7
3.2.2. End.AN.CI.D.T: SR-Aware Service Dynamic Context
Indicator with Variable Context Information in SRH Tag......7
3.2.3. End.AN.CI.D.V: SR-Aware Service Dynamic Context
Indicator with Variable Context Information in SRH TLV......7
3.2.4. End.AN.CI.D.D: SR-Aware Service Dynamic Context
Indicator with Variable Context Information in DOH..........8
4. Implementation Status..........................................8
4.1. H3C's Commercial Delivery.................................8
5. Security Considerations........................................9
6. IANA Considerations............................................9
7. References.....................................................9
7.1. Normative References......................................9
7.2. Informative References...................................10
Authors' Addresses...............................................11
1. Introduction
Segment Routing (SR) [RFC8402] leverages the source routing
paradigm. A node steers a packet through an SR Policy instantiated
as an ordered list of instructions called "segments". Segment
Routing (SR) can be applied to the IPv6 data plane using Segment
Routing Header (SRH) [RFC8754], which is called SRv6.
The segments may encode simple routing instructions for forwarding
packets along a specific network path, but also steer them through
VNFs or physical service appliances available in the network. [I-
D.ietf-spring-sr-service-programming] describes how a service can be
associated with a SID (Segment Identifier) and how these service
SIDs are integrated within an SR policy.
Services are categorized in two types, SR-aware and SR-unaware
services, depending on their SR handling capability. An SR-aware
service can directly process the SR information embedded in received
packets, while an SR-unaware service does not possess such
capability. [I-D.ietf-spring-sr-service-programming] defines an SRv6
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Endpoint Behavior, End.AN, for SR-aware functions, which is not
adequate, especially when service function nodes have difficulty in
ascertaining how to process the packet based solely on its
characteristics, such as 5-tuple.
A context indicator which is embedded in packets by the headend
provides subsequent service function nodes with the context on how to
process the packet. This is feasible because packets entering the
headend often exhibit more information, such as details about the
receiving interface, than their basic characteristics suggest,
facilitating the headend in identifying the traffic flow to which the
packet belongs. Therefore, the headend can extract this information,
embed it in a SID or elsewhere in the packet header and use it as the
basis for service function nodes to process the packet. This basis is
referred to as context indicators, and the subsequent processing on
service function nodes is performed based on this context.
In some instances, a SID can be directly associated with such function
of context indicator in the SR-aware services. For example, an SR-
aware firewall may use a context indicator SID to identify the specific
virtual firewall instance when applying VPN-specific rules for inner
packets.
In other instances, a context indicator SID can be dynamically
associated with a bunch of contexts, and indicate the SR-aware service
function nodes to identify the particular context with additional
information carried in the packet. When such dynamic context indicator
SID is included in the SR Policy, the additional context information
is needed to direct packet processing. This information can be supplied
either by the headend node to fill the relevant field according to the
traffic flow, or by reusing the identifier already encapsulated by the
client-side device to identify services.
This document describes how to use SRv6 SIDs as context indicator
for SR-aware services. These SIDs are called SRv6 Context Indicator
SIDs. The corresponding Endpoint behaviors for SRv6 Context
Indicator SIDs are defined in this document.
2. Use Case
In data center, Policy-Based Routing (PBR) is typically employed to
orchestrate Service Function Chain(SFC). To differentiate between
tenants and subsequently provide them with personalized value-added
services, VLANs and VPN instances are deployed in different layer-3
sub-interfaces, serving the purpose of isolating tenants from one
another, given that the traffic characteristics of these tenants may
overlap. Moreover, even when the traffic of all tenants necessitates
processing by the same virtual firewall (vFW), the specific service
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reqiured by individual tenants may vary, making Service Functions (SFs)
have to differentiate their traffic.
For instance, as in shown in figure 1, the traffic of tenant A
enters vFW through a 3-layer sub-interface with VLAN 'a', while
tenant B' s traffic enters through that of VLAN 'b'. With the
existence of VLANs and VPN instances, vFW would be able to figure
out tenants and select their exclusive vsys instances to supply
service. For example, the traffic of tenant A with destined for
address X would be dropped by vsys1 instance on vFW, while tenant
B's traffic with destination address Y will be dropped by vsys2
instance. This PBR method necessitates manual configuration and has
drawbacks such as complexity in configuration.
+------+
|vsys1 |vFW
-+vsys2 |
/ |... |
/ +------+
/
/ +------+
/ |vsys1 |vIPS
+--+ +----+ |vsys2 |
|GW+---+TOR1+------|... |
+--+ +----+ | |
\ +------+
\
\
\ +------+
\ |vsys1 |vAV
-+vsys2 |
|... |
| |
+------+
Figure 1
With the emergence of SRv6, its inherent programmability makes it
suitable for SFC orchestration. However, the current SRv6 SID could
accurately steer packets to a specified service node, for instance,
through the utilization of END.AN, but it falls short in communicating
to the node the specific service (e.g. vsys instance in security
resource pool scenario) that the packets require. Therefore, it is of
significant importance to extend and specify END.AN.
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3. SRv6 Context Indicator SIDs
An SRv6 Context Indicator SID is associated with a local context on
the SR-aware service node. It instructs the node to process the
packet by using the specific context.
This document defines new types of Endpoint behaviors for SRv6
Context Indicator SID, End.AN.CI.S and End.AN.CI.D (including
End.AN.CI.D.A, End.AN.CI.D.T, End.AN.CI.D.V, and End.AN.CI.D.D),
which are variants of the End.AN behavior [I-D.ietf-spring-sr-
service-programming]. End.AN.CI.S is statically associated with one
particular context. End.AN.CI.D (including End.AN.CI.D.A,
End.AN.CI.D.T, End.AN.CI.D.V, and End.AN.CI.D.D) is dynamically
associated with a bunch of local contexts, and additional variable
information carried in the packet is used to identify the particular
context.
3.1. End.AN.CI.S: SR-Aware Service Static Context Indicator
The "Endpoint with SR-Aware Service Static Context Indicator"
behavior ("End.AN.CI.S" for short) is a variant of the End.AN
behavior.
One of the applications of the End.AN.CI.S behavior is the SR-aware
firewall use case where the associated context identifies a specific
virtual firewall instance.
When N receives a packet whose IPv6 DA is S and S is a local
End.AN.CI.S SID associated with a local context C, N does the
following:
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S01. When an SRH is processed {
S02. If (Segments Left == 0) {
S03. Proceed to process the next header in the packet.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or
(Segments Left > Last Entry+1)) {
S10. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet.
S11. }
S12. Set the packet's associated context to C and perform service
S13. Decrement IPv6 Hop Limit by 1
S14. Decrement Segments Left by 1
S15. Update IPv6 DA with Segment List[Segments Left]
S16. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination
S17. }
3.2. End.AN.CI.D: SR-Aware Service Dynamic Context Indicator
The "Endpoint with SR-Aware Service Dynamic Context Indicator"
behavior ("End.AN.CI.D" for short) is a variant of the End.AN
behavior.
When N receives a packet whose IPv6 DA is S and S is a local
End.AN.CI.D SID, the line S12 from the End.AN.CI.S processing is
replaced by the following:
S12. Set the packet's associated context by using variable
context information carried in the packet and
perform service.
S13. If (the context information cannot be understood) {
S14. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered)
and Pointer set to the context information field,
interrupt packet processing, and discard the packet.
S15. }
There are four sub-types of End.AN.CI.D SID, carrying variable
context information associated with the End.AN.CI.D SID in different
positions:
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o End.AN.CI.D.A: Arguments in SID
o End.AN.CI.D.T: SRH Tag
o End.AN.CI.D.V: SRH TLV for context
o End.AN.CI.D.D: New options in DoH before SRH
3.2.1. End.AN.CI.D.A: SR-Aware Service Dynamic Context Indicator with
Variable Context Information in Arguments
The behavior also takes an argument: "Arg.VCI". This argument
provides variable context information for service. In this case, the
line S12 from the End.AN.CI.D processing is as the following:
S12. Set the packet's associated context by using variable
context information carried in the Arg.VCI and
perform service
3.2.2. End.AN.CI.D.T: SR-Aware Service Dynamic Context Indicator with
Variable Context Information in SRH Tag
The Tag field in SRH could be used to carry variable context
information. In this case, the line S12 from the End.AN.CI.D
processing is as the following:
S12. Set the packet's associated context by using variable
context information carried in the SRH Tag and
perform service
3.2.3. End.AN.CI.D.V: SR-Aware Service Dynamic Context Indicator with
Variable Context Information in SRH TLV
Optional TLV in SRH could be extended for variable context
information, which is used together with End.AN.CI.D. The Context
Information TLV has the following format:
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 | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Context Information (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In this case, the line S12 from the End.AN.CI.D processing is as the
following:
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S12. Set the packet's associated context by using variable
context information carried in the SRH Context
Information TLV and perform service
3.2.4. End.AN.CI.D.D: SR-Aware Service Dynamic Context Indicator with
Variable Context Information in DOH
Variable context information could also be carried through DOH for
the specified segment. The definition of such DOH Option is outside
the scope of this document.
In this case, the line S12 from the End.AN.CI.D processing is as the
following:
S12. Set the packet's associated context by using variable
context information carried in the DOH and perform
service
4. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to [RFC7942].
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of
this Internet-Draft, and is based on a proposal described in
[RFC7942]. The description of implementations in this section is
intended to assist the IETF in its decision processes in progressing
drafts to RFCs. Please note that the listing of any individual
implementation here does not imply endorsement by the IETF.
Furthermore, no effort has been spent to verify the information
presented here that was supplied by IETF contributors. This is not
intended as, and must not be construed to be, a catalog of available
implementations or their features. Readers are advised to note that
other implementations may exist.
According to [RFC7942], "this will allow reviewers and working
groups to assign due consideration to documents that have the
benefit of running code, which may serve as evidence of valuable
experimentation and feedback that have made the implemented
protocols more mature. It is up to the individual working groups to
use this information as they see fit".
4.1. H3C's Commercial Delivery
The feature has been implemented on H3C Comware V7.
* Organization: H3C
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* Implementation: H3C's Commercial Delivery implementation based
on Comware V7.
* Description: The implementation has been done.
* Maturity Level: Product
* Contact: linchangwang.04414@h3c.com
5. Security Considerations
TBD
6. IANA Considerations
This I-D requests the IANA to allocate, within the "SRv6 Endpoint
Behaviors" sub-registry belonging to the top-level "Segment-routing
with IPv6 dataplane (SRv6) Parameters" registry, the following
allocations:
Value Description Reference
--------------------------------------
0x00A9 End.AN.CI.S [This.ID]
0x00AA End.AN.CI.D.A [This.ID]
0x00AB End.AN.CI.D.T [This.ID]
0x00AC End.AN.CI.D.V [This.ID]
0x00AD End.AN.CI.D.D [This.ID]
7. References
7.1. Normative References
[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>.
[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>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/rfc/rfc8402>.
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[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/rfc/rfc8754>.
[I-D.ietf-spring-sr-service-programming] Clad, F., Xu, X., Filsfils,
C., Bernier, D., Li, C., Decraene, B., Ma, S., Yadlapalli,
C., Henderickx, W., and S. Salsano, "Service Programming
with Segment Routing", Work in Progress, Internet-Draft,
draft-ietf-spring-sr-service-programming-11, 23 February
2025, <https://www.ietf.org/archive/id/draft-ietf-spring-
sr-service-programming-11.txt>.
7.2. Informative References
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205, RFC
7942, DOI 10.17487/RFC7942, July 2016, <https://www.rfc-
editor.org/info/rfc7942>.
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Authors' Addresses
Jiaming Ye
China Mobile
China
Email: yejiaming@chinamobile.com
Changwang Lin
New H3C Technologies
China
Email: linchangwang.04414@h3c.com
Dongjie Lu
China Mobile
China
Email: ludongjie@chinamobile.com
Meiling Chen
China Mobile
China
Email: chenmeiling@chinamobile.com
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