Internet DRAFT - draft-li-idr-bgpls-sr-policy-composite-path
draft-li-idr-bgpls-sr-policy-composite-path
Network Working Group H. Li
Internet-Draft M. Chen
Intended status: Standards Track C. Lin
Expires: 29 August 2024 New H3C Technologies
W. Jiang
W. Cheng
China Mobile
26 February 2024
Signaling Composite Candidate Path of SR Policy using BGP-LS
draft-li-idr-bgpls-sr-policy-composite-path-06
Abstract
Segment Routing is a source routing paradigm that explicitly
indicates the forwarding path for packets at the ingress node. An SR
Policy is associated with one or more candidate paths, and each
candidate path is either dynamic, explicit or composite. This
document specifies the extensions to BGP Link State (BGP-LS) to carry
composite candidate path information in the advertisement of an SR
policy.
Status of This Memo
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This Internet-Draft will expire on 29 August 2024.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. BGP-LS Extensions for Composite Candidate Path . . . . . . . 3
3.1. Constituent SR Policy TLV . . . . . . . . . . . . . . . . 3
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
As described in [RFC7752], BGP Link State (BGP-LS) provides a
mechanism by which link-state and TE information can be collected
from networks and shared with external components using the BGP
routing protocol.
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].
An SR Policy is associated with one or more candidate paths. A
composite candidate path acts as a container for grouping of SR
Policies. As described in section 2.2 in [RFC9256], the composite
candidate path construct enables combination of SR Policies, each
with explicit candidate paths and/or dynamic candidate paths with
potentially different optimization objectives and constraints, for a
load-balanced steering of packet flows over its constituent SR
Policies.
[I-D.draft-jiang-spring-parent-sr-policy-use-cases] describes some
use cases for SR policy group composite candidate path.
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[I-D.draft-ietf-idr-bgp-ls-sr-policy] describes a mechanism to
collect the SR policy information that is locally available in a node
and advertise it into BGP-LS updates. This document extends it to
provide some extra information to carry composite candidate path
information in the BGP-LS advertisement.
2. Terminology
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. BGP-LS Extensions for Composite Candidate Path
[RFC7752] defines the BGP-LS NLRI that can be a Node NLRI, a Link
NLRI or a Prefix NLRI. The corresponding BGP-LS attribute is a Node
Attribute, a Link Attribute or a Prefix Attribute.
[I-D.draft-ietf-idr-bgp-ls-sr-policy] describes a mechanism to
collect the SR Policy information that is locally available in a node
and advertise it into BGP Link State (BGP-LS) updates. This section
defines a new sub-TLV which is carried in the optional non-transitive
BGP Attribute "LINK_STATE Attribute" defined in [RFC7752].
3.1. Constituent SR Policy TLV
Segment Routing Policy (SR Policy) architecture is specified in
[RFC9256]. A SR Policy can comprise of one or more candidate paths,
and each candidate path is either dynamic, explicit or composite. A
composite candidate path can comprise of one or more constituent SR
policies. The endpoints of the constituent SR Policies and the
parent SR Policy MUST be identical, and the colors of each of the
constituent SR Policies and the parent SR Policy MUST be different.
The Constituent SR Policy TLV is used to report the constituent SR
policy(s) of a composite candidate path. The TLV has 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
* Type: to be assigned by IANA.
* Length: the total length of the value field not including Type and
Length fields.
* Reserved: 32 bits reserved and MUST be set to 0 on transmission
and MUST be ignored on receipt.
* Color: 4 octets that indicates the color of the constituent SR
Policy.
* Weight: 4 octet field that indicates the weight associated with
the SID-List for weighted load-balancing. Refer Section 2.2 and
2.11 of [RFC9256].
* Sub-TLVs: no sub-TLV is currently defined.
4. Operations
The document does not bring new operation beyond the description of
operations defined in [RFC7752] and
[I-D.draft-ietf-idr-bgp-ls-sr-policy]. The existing operations
defined in [RFC7752] and [I-D.draft-ietf-idr-bgp-ls-sr-policy] can
apply to this document directly.
Typically but not limit to, the BGP-LS messages carring composite
candidate path information along with the SR policy are distributed
to a controller.
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After configuration, the composite candidate path information will be
advertised by BGP update messages. The operation of advertisement is
the same as defined in [RFC7752] and
[I-D.draft-ietf-idr-bgp-ls-sr-policy], as well as the receiption.
5. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the security considerations discussed in
[I-D.draft-ietf-idr-bgp-ls-sr-policy].
6. IANA Considerations
This document defines a new TLV in the BGP-LS Link Descriptor and
Attribute TLVs:
+=======+===========================+===============+
| Value | Description | Reference |
+=======+===========================+===============+
| TBA | Constituent SR Policy TLV | This document |
+-------+---------------------------+---------------+
Table 1
7. References
7.1. Normative References
[I-D.draft-ietf-idr-bgp-ls-sr-policy]
Previdi, S., Talaulikar, K., Dong, J., Gredler, H., and J.
Tantsura, "Advertisement of Segment Routing Policies using
BGP Link-State", Work in Progress, Internet-Draft, draft-
ietf-idr-bgp-ls-sr-policy-03, 5 November 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
ls-sr-policy-03>.
[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>.
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[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>.
7.2. Informative References
[I-D.draft-jiang-spring-parent-sr-policy-use-cases]
Jiang, W., Cheng, W., Lin, C., and Y. Qiu, "Use Cases for
Parent SR Policy", Work in Progress, Internet-Draft,
draft-jiang-spring-parent-sr-policy-use-cases-03, 5
January 2024, <http://www.ietf.org/internet-drafts/draft-
jiang-spring-parent-sr-policy-use-cases-03.txt>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC9256] Filsfils, C., Talaulikar, K., 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>.
Authors' Addresses
Hao Li
New H3C Technologies
Email: lihao@h3c.com
Mengxiao Chen
New H3C Technologies
Email: chen.mengxiao@h3c.com
Changwang Lin
New H3C Technologies
Email: linchangwang.04414@h3c.com
Wenying Jiang
China Mobile
Email: jiangwenying@chinamobile.com
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Weiqiang Cheng
China Mobile
Email: chengweiqiang@chinamobile.com
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