Advertisement of Algorithm in BGP
draft-lp-idr-bgp-algorithm-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Yao Liu , Shaofu Peng | ||
| Last updated | 2025-11-02 | ||
| Replaces | draft-lp-lsr-bgp-algorithm | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-lp-idr-bgp-algorithm-00
IDR Working Group Y. Liu
Internet-Draft Shaofu. Peng
Intended status: Standards Track ZTE Corporation
Expires: 6 May 2026 2 November 2025
Advertisement of Algorithm in BGP
draft-lp-idr-bgp-algorithm-00
Abstract
This document proposes extensions to BGP to support algorithm-based
end-to-end path establishment.
Status of This Memo
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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 6 May 2026.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
3. Algorithm Extended Community . . . . . . . . . . . . . . . . 2
4. Algo-based Inter-domain Path . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
[RFC9350] proposes a solution that allows IGPs themselves to compute
constraint-based paths over the SR network. [RFC9502] allows flex-
algo to be deployed in any IP network, even in the absence of SR-MPLS
and SRv6.
However, the algorithm-based path can only be used in the IGP domain.
In the BGP-based inter-domain scenario, end-to-end path based on
algorithms cannot be supported.
This document proposes extensions to BGP to support algorithm-based
end-to-end path establishment.
2. Conventions used in this document
2.1. 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.
3. Algorithm Extended Community
This document defines a new transitive BGP Extended Communities
Attribute[RFC4360]. This new Extended Community has the following
encoding, where:
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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=0x03 | Sub-Type=TBA1 | Flags | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Reserved (4 Octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Algorithm Extended Community
Type: 1 octet. The value is 0x03.
Sub-Type: 1 octet. TBA1
Flags: 1 octet. Unused, MUST be set to 0 and ingored on receipt.
Algorithm: 1 octet specifying IGP Algorithm Types. Value from 0
to 255.
Reserved: 4 Octets. MUST be set to 0, ignored at reception
4. Algo-based Inter-domain Path
+----------------------+ +----------------------+
| | 2 | | | | 6 | |
| +---+ | | +---+ |
| | | |
| Flex-algo 128 | | Flex-algo 128 |
| | | |
|---+ +---+ +---+ +---|
| 1 |----------------| 4 |---------| 5 |----------------| 8 |
|---+ +---+ +---+ +---|
| | | |
| Flex-algo 129 | | Flex-algo 129 |
| | | |
| +---+ | | +---+ |
| | 3 | | | | 7 | |
+----------------------+ +----------------------+
|<-----IGP Domain1---->| |<-----IGP Domain2---->|
Figure 2: Algo-based Inter-domain Path
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As shown in Figure 2, node 8 is configured with two loopback
addresses, loopback-1 and loopback-2, they belong to the flex-algo
128 plane and the flex-algo 129 plane respectively. In IGP domain 2,
the routes to loopback-1 will be generated on the nodes (e.g, node
5,6,8) in the Flex-algo 128 plane and the routes to loopback-2 will
be generated on the nodes (e.g, node 5,7,8) in the Flex-algo 129
plane.
Node 5 can advertise prefix loopback-1 and prefix loopback-2 to node
4 through BGP[RFC2545][RFC4271]. Node 4 can import the BGP routes
into IGP and continue to advertise the routes to its neighbors in IGP
domain1. Or, node 4 directly advertises the routes to node 1 through
BGP.
In both cases, the corresponding algorithm information from IGP
domain2 is lost during the advertisement. As a result, node 4 does
not know which Flex-algo plane to import loopback-1 or loopback-2
into IGP domain 1.
With the Algorithm Extended Community, the algorithm information can
be carried in the BGP route of loopbacks advertised from node 5 to
node 4.
The administrator can configure algorithms in each IGP domain in the
network. A simple configuration method is that algorithms in each
IGP domain are consistent. If the algorithm configurations in each
IGP domain are inconsistent, the ASBR needs to know the mapping
relationship of the algorithms and carry the converted algorithm
information in Algorithm Extended Community when advertising the BGP
route.
A BGP speaker can advertise multiple paths for the same address
prefix, each path is identified by a Path Identifier in addition to
the address prefix [RFC7911]. By leveraging add-path, multiple
loopbacks on the egress node can be avoided.
Same approach is applicable for SRv6 locator which is also advertised
via [RFC2545] , SR-MPLS BGP Prefix SID advertisement[RFC8669] and BGP
Labeled Unicast(BGP-LU)[RFC8227]. If any Router Reflector existed in
the network, it SHOULD support this new Extended Community.
5. Security Considerations
TBD
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6. IANA Considerations
IANA is requested to allocate the sub-type TBA1 for "Algorithm
Extended Community" under the "BGP Transitive Opaque Extended
Community"
Sub-type Value Name Reference
----------------------------------------------------------------
TBA1 Algorithm Extended Community This document
7. References
7.1. Normative References
[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>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.
[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>.
[RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
DOI 10.17487/RFC9350, February 2023,
<https://www.rfc-editor.org/info/rfc9350>.
[RFC9502] Britto, W., Hegde, S., Kaneriya, P., Shetty, R., Bonica,
R., and P. Psenak, "IGP Flexible Algorithm in IP
Networks", RFC 9502, DOI 10.17487/RFC9502, November 2023,
<https://www.rfc-editor.org/info/rfc9502>.
7.2. Informative References
[RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
Extensions for IPv6 Inter-Domain Routing", RFC 2545,
DOI 10.17487/RFC2545, March 1999,
<https://www.rfc-editor.org/info/rfc2545>.
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[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC8227] Cheng, W., Wang, L., Li, H., van Helvoort, H., and J.
Dong, "MPLS-TP Shared-Ring Protection (MSRP) Mechanism for
Ring Topology", RFC 8227, DOI 10.17487/RFC8227, August
2017, <https://www.rfc-editor.org/info/rfc8227>.
[RFC8669] Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah,
A., and H. Gredler, "Segment Routing Prefix Segment
Identifier Extensions for BGP", RFC 8669,
DOI 10.17487/RFC8669, December 2019,
<https://www.rfc-editor.org/info/rfc8669>.
Authors' Addresses
Liu Yao
ZTE Corporation
Email: liu.yao71@zte.com.cn
Peng Shaofu
ZTE Corporation
Email: peng.shaofu@zte.com.cn
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