Internet DRAFT - draft-ietf-idr-sr-policy-seglist-id
draft-ietf-idr-sr-policy-seglist-id
IDR C. Lin
Internet Draft New H3C Technologies
Intended status: Standards Track W. Cheng
Expires: June 17, 2024 China Mobile
Y. Liu
ZTE
K. Talaulikar
Cisco Systems
M. Chen
New H3C Technologies
December 17, 2023
BGP SR Policy Extensions for Segment List Identifier
draft-ietf-idr-sr-policy-seglist-id-00
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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Copyright Notice
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Table of Contents
1. Introduction...................................................3
1.1. Requirements Language.....................................3
2. Segment List Identifier in SR Policy...........................4
2.1. Segment List ID Sub-TLV...................................5
3. Security Considerations........................................5
4. IANA Considerations............................................6
5. References.....................................................6
5.1. Normative References......................................6
5.2. Informative References....................................6
Authors' Addresses................................................7
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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-
segment-routing-te-policy] 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.
For example, a network controller distributes SR policies to the
headend nodes, and the headend nodes 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.
For another example, 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. So,
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.
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2. Segment List Identifier in SR Policy
As defined in [I-D.ietf-idr-segment-routing-te-policy], 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:
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.
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When signaling SR Policy by PCEP [I-D.ietf-pce-multipath], 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.
The Segment List ID sub-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 | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Segment List ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: TBD.
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 octet of ID for the segment list.
3. Security Considerations
The security requirements and mechanisms described in [I-D.ietf-idr-
segment-routing-te-policy] also apply to this document.
This document does not introduce any new security consideration.
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4. IANA Considerations
This document defines a new Sub-TLV in the registry "SR Policy
Segment List Sub-TLVs" [I-D.ietf-idr-segment-routing-te-policy]:
Value Description Reference
-------------------------------------------------------
TBA Segment List ID sub-TLV This document
5. References
5.1. 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-segment-routing-te-policy] 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-segment-routing-te-policy-
25, 26 September 2023, <http://www.ietf.org/internet-
drafts/draft- ietf-idr-segment-routing-te-policy-25.txt>.
5.2. 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>.
[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-09, 24 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
multipath-09>.
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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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