BGP Extensions of SR Policy for Composite Candidate Path
draft-li-idr-sr-policy-composite-path-00
Network Working Group H. Li
Internet-Draft M. Chen
Intended status: Standards Track C. Lin
Expires: August 6, 2021 H3C
February 2, 2021
BGP Extensions of SR Policy for Composite Candidate Path
draft-li-idr-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. A candidate
path is either dynamic, explicit or composite. This document defines
extensions to BGP to distribute SR policies carrying composite
candidate path information. So that composite candidate paths can be
installed when the SR policy is applied.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Constituent SR Policy Attributes in SR Policy . . . . . . . . 3
3.1. Constituent SR Policy Sub-TLV . . . . . . . . . . . . . . 4
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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
[I-D.ietf-spring-segment-routing-policy]. In order to distribute SR
policies to the headend, [I-D.ietf-idr-segment-routing-te-policy]
specifies a mechanism by using BGP.
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.
This document defines extensions to Border Gateway Protocol (BGP) to
distribute SR policies carrying composite candidate path information.
So that composite candidate paths can be installed when the SR policy
is applied.
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
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Constituent SR Policy Attributes 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
...
...
As described in section 2.2 in
[I-D.ietf-spring-segment-routing-policy], 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. Therefore a constituent SR Policy is
referenced only by color in the composite candidate path since its
headend and endpoint are identical to the parent SR policy.
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SR policy with composite candidate path information 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
Segment
...
Constituent SR Policy
Weight
...
3.1. Constituent SR Policy Sub-TLV
The Constituent SR Policy sub-TLV encodes a single composite path
towards the endpoint. The Constituent SR Policy sub-TLV is an
optional sub-TLV of BGP Tunnel Encapsulation Attribute, and MAY
appear multiple times in the SR Policy encoding. The ordering of
Constituent SR Policy sub-TLVs does not matter. The Constituent SR
Policy sub-TLV MAY contain a Weight sub-TLV.
Since a candidate path is either dynamic, explicit or composite, the
Constituent SR Policy sub-TLV and the Segment List sub-TLV SHOULD NOT
appear in the same BGP Tunnel Encapsulation Attribute.
The Constituent SR Policy 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 | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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: 2 octet of reserved bits. SHOULD be set to zero on
transmission and MUST be ignored on receipt.
o Color: 4-octet value identifying the constituent SR policy.
o sub-TLVs currently defined:
* An optional single Weight sub-TLV which is defined in section
2.4.4.1 in [I-D.ietf-idr-segment-routing-te-policy]. According
to [I-D.ietf-spring-segment-routing-policy], the fraction of
flows steered into each constituent SR Policy is equal to the
relative weight of each constituent SR Policy.
4. Operations
The document does not bring new operation beyond the description of
operations defined in [I-D.ietf-idr-segment-routing-te-policy]. The
existing operations defined in
[I-D.ietf-idr-segment-routing-te-policy] can apply to this document
directly.
Typically but not limit to, the SR policies carrying composite
candidate path information are configured by a controller.
After configuration, the SR policies carrying path composite
candidate path information will be advertised by BGP update messages.
The operation of advertisement is the same as defined in
[I-D.ietf-idr-segment-routing-te-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.ietf-idr-segment-routing-te-policy].
6. IANA Considerations
This document defines a new Sub-TLV in registries "SR Policy List
Sub-TLVs" [I-D.ietf-idr-segment-routing-te-policy]:
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+-------+-------------------------------+---------------+
| Value | Description | Reference |
+-------+-------------------------------+---------------+
| TBA | Constituent SR Policy Sub-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-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Rosen, E., Jain, D., and S. Lin, "Advertising Segment
Routing Policies in BGP", draft-ietf-idr-segment-routing-
te-policy-11 (work in progress), November 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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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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