Internet DRAFT - draft-lin-spring-srv6-aware-context-indicator
draft-lin-spring-srv6-aware-context-indicator
SPRING Working Group C. Lin
Internet Draft New H3C Technologies
Intended status: Standards Track D. Lu
Expires: June 17, 2024 M. Chen
China Mobile
M. Chen
New H3C Technologies
December 20, 2023
SRv6 Context Indicator SIDs for SR-Aware Services
draft-lin-spring-srv6-aware-context-indicator-01
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.
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Table of Contents
1. Introduction...................................................2
2. SRv6 Context Indicator SIDs....................................3
2.1. End.AN.CI.S: SR-Aware Service Static Context Indicator....3
2.2. End.AN.CI.D: SR-Aware Service Dynamic Context Indicator...4
2.2.1. End.AN.CI.D.A: SR-Aware Service Dynamic Context
Indicator with Variable Context Information in Arguments....5
2.2.2. End.AN.CI.D.T: SR-Aware Service Dynamic Context
Indicator with Variable Context Information in SRH Tag......5
2.2.3. End.AN.CI.D.V: SR-Aware Service Dynamic Context
Indicator with Variable Context Information in SRH TLV......6
2.2.4. End.AN.CI.D.D: SR-Aware Service Dynamic Context
Indicator with Variable Context Information in DOH before SRH
............................................................6
3. Security Considerations........................................6
4. IANA Considerations............................................6
5. References.....................................................7
5.1. Normative References......................................7
Authors' Addresses................................................8
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. An SR-aware service can process the SR information in the
packets it receives. [I-D.ietf-spring-sr-service-programming]
defines an SRv6 Endpoint Behavior, End.AN, for SR-aware function.
But service-specific functions are not defined.
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A context indicator provides the context on how to process the
packet for service nodes. A SID can be 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 some cases, a context indicator SID can be dynamically associated
with a bunch of contexts, and indicate the SR-aware service nodes to
identify the particular context with additional information carried
in the packet. When such dynamic context indicator SID is contained
in the SR Policy, the headend node will fill additional context
information in the corresponding field of the packet, based on which
traffic flow the packet belongs to. The End.AN SID defined in [I-
D.ietf-spring-sr-service-programming] is not adequate for context
indicators, especially for the dynamic ones. Because End.AN is too
abstract and general for the headend node to determine its actions.
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. 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.
2.1. 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.
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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:
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. }
2.2. 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:
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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:
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
2.2.1. 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
2.2.2. 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:
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S12. Set the packet's associated context by using variable
context information carried in the SRH Tag and
perform service
2.2.3. 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:
S12. Set the packet's associated context by using variable
context information carried in the SRH Context
Information TLV and perform service
2.2.4. End.AN.CI.D.D: SR-Aware Service Dynamic Context Indicator with
Variable Context Information in DOH before SRH
Variable context information could also be carried through DOH
before SRH 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
3. Security Considerations
TBD
4. IANA Considerations
This I-D requests the IANA to allocate, within the "SRv6 Endpoint
Behaviors" sub-registry belonging to the top-level "Segment-routing
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with IPv6 dataplane (SRv6) Parameters" registry, the following
allocations:
Value Description Reference
--------------------------------------
TBA-1 End.AN.CI.S [This.ID]
TBA-2 End.AN.CI.D.A [This.ID]
TBA-3 End.AN.CI.D.T [This.ID]
TBA-4 End.AN.CI.D.V [This.ID]
TBA-5 End.AN.CI.D.D [This.ID]
5. References
5.1. 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>.
[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-08, 21 August
2023, <https://www.ietf.org/archive/id/draft-ietf-spring-
sr-service-programming-08.txt>.
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Authors' Addresses
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
Mengxiao Chen
New H3C Technologies
China
Email: chen.mengxiao@h3c.com
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