IDR C. Lin
Internet Draft New H3C Technologies
Intended status: Standards Track W. Cheng
Expires: August 24, 2025 China Mobile
Y. Liu
ZTE
K. Talaulikar
Cisco Systems
M. Chen
New H3C Technologies
February 24, 2025
BGP SR Policy Extensions for Segment List Identifier
draft-ietf-idr-sr-policy-seglist-id-03
Abstract
Segment Routing is a source routing paradigm that explicitly
indicates the forwarding path for packets at the ingress node. An SR
Policy is a set of candidate paths, each consisting of one or more
segment lists. This document defines extensions to BGP SR Policy to
specify the identifier of segment list.
Status of this Memo
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Table of Contents
1. Introduction...................................................2
1.1. Requirements Language.....................................3
2. Segment List Identifier in SR Policy...........................3
2.1. Segment List ID Sub-TLV...................................4
3. Security Considerations........................................5
4. Implementation Status..........................................5
4.1. New H3C Technologies......................................6
4.2. ZTE Corp..................................................6
5. IANA Considerations............................................7
6. References.....................................................7
6.1. Normative References......................................7
6.2. Informative References....................................7
Authors' Addresses................................................9
1. Introduction
Segment routing (SR) [RFC8402] is a source routing paradigm that
explicitly indicates the forwarding path for packets at the ingress
node. The ingress node steers packets into a specific path according
to the Segment Routing Policy (SR Policy) as defined in [RFC9256].
In order to distribute SR policies to the headend, [I-D.ietf-idr-sr-
policy-safi] specifies a mechanism by using BGP.
However, there is no identifier for segment list in BGP SR Policy,
which may cause inconvenience for other mechanisms to designate
segment lists distributed by BGP.
Consider the case of a network controller distributing SR policies
to the headend nodes where the headend nodes need to collect traffic
forwarding statistics per segment list. When a headend node reports
each statistic to the controller, it needs to specify the segment
list which the statistic belongs to. Due to the lack of identifier,
the headend node usually reports all SIDs in the associated segment
list along with the statistic, and then the controller needs to
compare the SIDs one by one to recognize which segment list it is.
The advertisement of all SIDs in the segment list consumes a lot of
octets, and the comparison of SIDs can be complicated.
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Consider a second example where a network controller distributes SR
policies using BGP, and then it uses NETCONF to set some
configurations of the segment lists which are not suitable to be
carried in BGP. The controller needs to specify which segment list
these configurations belong to when it issues them. In this case, a
simple identifier of segment list can also be helpful.
An identifier of segment list may also serve as a user-friendly
attribute for debugging and troubleshooting purposes, such as
displaying an invalid segment list when its associated BFD session
is down.
This document defines extensions to BGP SR Policy to specify the
identifier of segment list.
1.1. 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.
2. Segment List Identifier in SR Policy
As defined in [I-D.ietf-idr-sr-policy-safi], the SR policy encoding
structure is as follows:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
SRv6 Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment
Segment
...
...
SR policy with segment list identifier is expressed as below:
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SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
SRv6 Binding SID
Preference
Priority
Policy Name
Policy Candidate Path Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment List Identifier
Segment
Segment
...
...
The segment list identifier can be advertised using the Segment List
ID sub-TLV, as defined in Section 2.1.
When signaling SR Policy by PCEP [I-D.ietf-pce-multipath] (see
section 5.2), a segment list is identified by "Path ID", which is a
4-octet identifier. In this document, the segment list identifier is
also represented using a 4-octet ID.
2.1. Segment List ID Sub-TLV
The Segment List ID sub-TLV specifies the identifier of the segment
list by a 4-octet number. The Segment List ID is unique within the
context of a Candidate Path.
The Segment List ID sub-TLV is optional and it MUST NOT appear more
than once inside the Segment List sub-TLV. If multiple instances are
present, then the first one is considered valid and the rest are
ignored.
The Segment List ID sub-TLV has the following format:
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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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Segment List ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: TBD(19).
o Length: 6.
o Flags: 1 octet of flags. None are defined at this stage. Flags
SHOULD be set to zero on transmission and MUST be ignored on
receipt.
o RESERVED: 1 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o Segment List ID: 4 octets which carry a 32-bit unsigned non-zero
number that serves as the identifier associated with the segment
list. A value of 0 indicates that there is no identifier
associated with the Segment List. The scope of this identifier is
the SR Policy Candidate path.
3. Security Considerations
The security requirements and mechanisms described in [I-D.ietf-idr-
sr-policy-safi] also apply to this document.
This document does not introduce any new security consideration.
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
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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. New H3C Technologies
* Organization: New H3C Technologies.
* Implementation: H3C CR16000, CR19000 series routers
implementation.
* Description: All sections including all the "MUST" and "SHOULD"
clauses have been implemented in above-mentioned New H3C
Products(running Version 7.1.099 and above).
* Maturity Level: Product
* Coverage: All sections.
* Version: Draft-03
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: linchangwang.04414@h3c.com
* Last updated: February 10, 2025
4.2. ZTE Corp
* Organization: ZTE Corporation
* Implementation: ZTE's ZXR10 core router
* Description: The implementation in lab has been completed. The
commercial implementation is under development.
* Maturity Level: Product
* Coverage: All
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* Version: Draft-03
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: feng.jun99@zte.com.cn
* Last updated: February 6, 2025
5. IANA Considerations
This document defines a new Sub-TLV in the registry "SR Policy
Segment List Sub-TLVs" [I-D.ietf-idr-sr-policy-safi]:
Value Description Reference
-------------------------------------------------------
TBA (19) Segment List ID sub-TLV This document
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, May 2017
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[I-D.ietf-idr-sr-policy-safi] Previdi, S., Filsfils, C., Talaulikar,
K., Mattes, P., and D. Jain, "Advertising Segment Routing
Policies in BGP", Work in Progress, Internet-Draft, draft-
ietf-idr-sr-policy-safi-13, 6 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
policy-safi-13>.
6.2. Informative References
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
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[I-D.ietf-pce-multipath] Koldychev, M., Sivabalan, S., Saad, T.,
Beeram, V. P., Bidgoli, H., Yadav, B., Peng, S., and G. S.
Mishra, "PCEP Extensions for Signaling Multipath
Information", Work in Progress, Internet-Draft, draft-
ietf-pce-multipath-12, 8 October 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
multipath-12>.
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Authors' Addresses
Changwang Lin
New H3C Technologies
China
Email: linchangwang.04414@h3c.com
Weiqiang Cheng
China Mobile
China
Email: chengweiqiang@chinamobile.com
Yao Liu
ZTE
China
Email: liu.yao71@zte.com.cn
Ketan Talaulikar
Cisco Systems
India
Email: ketant.ietf@gmail.com
Mengxiao Chen
New H3C Technologies
China
Email: chen.mengxiao@h3c.com
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