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Network Working Group H. Li
Internet-Draft M. Chen
Intended status: Standards Track C. Lin
Expires: August 6, 2021 H3C
February 2, 2021
Signaling Composite Candidate Path of SR Policy using BGP-LS
draft-li-idr-bgpls-sr-policy-composite-path-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 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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 6, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
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This document is subject to BCP 78 and the IETF Trust's Legal
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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 . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 5
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
[I-D.ietf-spring-segment-routing-policy].
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
[I-D.ietf-spring-segment-routing-policy], 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.ietf-idr-te-lsp-distribution] 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.
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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.ietf-idr-te-lsp-distribution] 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
[I-D.ietf-spring-segment-routing-policy]. 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:
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) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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where:
o Type: to be assigned by IANA.
o Length: the total length of the value field not including Type and
Length fields.
o Reserved: 32 bits reserved and MUST be set to 0 on transmission
and MUST be ignored on receipt.
o Color: 4 octets that indicates the color of the constituent SR
Policy.
o 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 [I-D.ietf-spring-segment-routing-policy].
o 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.ietf-idr-te-lsp-distribution]. The existing operations defined
in [RFC7752] and [I-D.ietf-idr-te-lsp-distribution] 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.
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.ietf-idr-te-lsp-distribution], 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.ietf-idr-te-lsp-distribution].
6. IANA Considerations
This document defines a new TLV in the BGP-LS Link Descriptor and
Attribute TLVs:
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+-------+---------------------------+---------------+
| Value | Description | Reference |
+-------+---------------------------+---------------+
| TBA | Constituent SR Policy TLV | This document |
+-------+---------------------------+---------------+
7. Contributors
In addition to the authors listed on the front page, the following
co-authors have also contributed to this document:
Yuanxiang Qiu
Liping Yang
Yang Wang
8. References
8.1. Normative References
[I-D.ietf-idr-te-lsp-distribution]
Previdi, S., Talaulikar, K., Dong, J., Chen, M., Gredler,
H., and J. Tantsura, "Distribution of Traffic Engineering
(TE) Policies and State using BGP-LS", draft-ietf-idr-te-
lsp-distribution-14 (work in progress), October 2020.
[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/info/rfc8402>.
8.2. Informative References
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-09 (work in progress),
November 2020.
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[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>.
Authors' Addresses
Hao Li
H3C
Email: lihao@h3c.com
Mengxiao Chen
H3C
Email: chen.mengxiao@h3c.com
Changwang Lin
H3C
Email: linchangwang.04414@h3c.com
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