LSVR L. Zhang
Internet-Draft J. Dong
Intended status: Standards Track Huawei Technologies
Expires: 4 September 2025 3 March 2025
Applying BGP-LS Segment Routing over IPv6(SRv6) Extensions to BGP-LS-SPF
draft-li-lsvr-bgp-spf-srv6-01
Abstract
For network scenarios such as Massively Scaled Data Centers (MSDCs),
BGP is extended for Link-State (LS) distribution and the Shortest
Path First (SPF) algorithm based calculation. BGP-LS-SPF leverages
the mechanisms of both BGP protocol and BGP-LS protocol extensions.
Segment Routing over IPv6 (SRv6) provides a source routing mechanism
that allows a flow to be restricted to a specific topological path,
while maintaining per-flow state only at the ingress node(s) to the
SRv6 domain. In some networks, it may be useful to enable SRv6 based
source routing mechanism together with BGP-LS-SPF. This document
proposes to introduce the BGP Link-State (BGP-LS) extensions for SRv6
to the BGP-LS-SPF SAFI.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 4 September 2025.
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/
license-info) in effect on the date of publication of this document.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. SRv6 Node Attribute TLVs . . . . . . . . . . . . . . . . . . 3
2.1. SRv6 Capabilities TLV . . . . . . . . . . . . . . . . . . 3
2.2. SRv6 Node MSD Types . . . . . . . . . . . . . . . . . . . 4
2.3. SR-Algorithm TLV . . . . . . . . . . . . . . . . . . . . 4
3. SRv6 Link Attribute TLVs . . . . . . . . . . . . . . . . . . 4
3.1. SRv6 End.X SID TLV . . . . . . . . . . . . . . . . . . . 5
3.2. L2 Bundele Member Attributes TLV . . . . . . . . . . . . 5
3.3. SRv6 Link MSD Types . . . . . . . . . . . . . . . . . . . 5
4. SRv6 Prefix Attribute TLVs . . . . . . . . . . . . . . . . . 5
4.1. SRv6 Locator TLV . . . . . . . . . . . . . . . . . . . . 6
5. SRv6 SID NLRI . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. SRv6 SID Information TLV . . . . . . . . . . . . . . . . 7
5.2. SRv6 Endpoint Behavior TLV . . . . . . . . . . . . . . . 7
5.3. SRv6 SID Structure TLV . . . . . . . . . . . . . . . . . 7
6. Operational Considerations . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
[I-D.ietf-lsvr-bgp-spf] extends BGP for Link-State (LS) distribution
and the Shortest Path First (SPF) algorithm based calculation. BGP-
LS-SPF leverages the mechanisms of both BGP protocol [RFC4271] and
BGP-LS protocol extensions [RFC9552], with the extensions to BGP-LS
attribute and new NLRI selection rules.
Segment Routing over IPv6 (SRv6) allows for a flexible definition of
end-to-end paths within various topologies by encoding paths as
sequences of topological or functional sub-paths called "segments".
SRv6 provides a mechanism that allows a flow to be restricted to a
specific topological path, while maintaining per-flow state only at
the ingress node(s) to the SRv6 domain.
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In network scenarios such as Data Center networks, WAN networks or
other networks where BGP-LS-SPF can be used as the underlay routing
protocol, it may be useful to enable SRv6 based source routing
mechanism for traffic engineering and optimization. This document
proposes to introduce the BGP Link-State (BGP-LS) extensions for SRv6
to the BGP-LS-SPF SAFI, and discusses which SRv6 extensions can be
applied to BGP-LS-SPF SAFI.
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.
2. SRv6 Node Attribute TLVs
Based on [RFC9514], the following SRv6 Node Attributes TLV SHOULD be
supported in BGP-LS-SPF.
+======+=======================+===========+
| Type | Description | Reference |
+======+=======================+===========+
| 1138 | SRv6 Capabilities TLV | RFC 9514 |
+------+-----------------------+-----------+
| 266 | Node MSD TLV | RFC 8814 |
+------+-----------------------+-----------+
| 1035 | SR Algorithm TLV | RFC 9085 |
+------+-----------------------+-----------+
Table 1: Node Attribute TLVs for SRv6
with BGP-LS-SPF
2.1. SRv6 Capabilities TLV
The SRv6 Capabilities TLV defined in [RFC9514] is used to announce
the SRv6 capabilities of the node along with the BGP-LS Node NLRI and
indicates the SRv6 support by the node.
For BGP-LS-SPF, it SHOULD support this TLV to announce the SRv6
capabilities of BGP-LS-SPF nodes. A single instance of this TLV MUST
be included in the BGP-SPF Node Attribute for each SRv6-capable node.
[RFC9514] defines the value of this TLV is copied from the ISIS SRv6
Capabilities sub-TLV or from the OSPFv3 SRv6 Capabilities TLV, but
both of them have the same flag definition, therefore, the flags
format of SRv6 Capabilities TLV of BGP-LS-SPF is consistent with that
in ISIS SRv6 Capabilities sub-TLV and OSPFv3 SRv6 Capabilities TLV.
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2.2. SRv6 Node MSD Types
The Node MSD TLV defined in [RFC8814] is used to advertise the limits
and the Segment Routing Header (SRH) operations supported by the
SRv6-capable node.
For BGP-LS-SPF, it SHOULD support this TLV to advertise the limits
and operations supported by BGP-LS-SPF node to enable segment
routing. The SRv6 MSD types specified in Section 4 of [RFC9352] are
also used with the BGP-LS-SPF Node MSD TLV.
The SRv6 Node MSD TLV is an optional TLV, for a specific MSD type, if
the advertised value is zero or no value is advertised, then the
headend can apply an SR Policy that only contains one segment without
inserting any SRH header.
2.3. SR-Algorithm TLV
[RFC9514] specifies that the algorithm support for SRv6 is advertised
via the SR-Algorithm TLV specified in [RFC9085]. The SR-Algorithm is
used to advertise the SR algorithms supported by the node.
This TLV is a basic TLV of SR and SHOULD be supported in BGP-LS-SPF.
The format of Algorithm fields in this TLV is consistent with that in
ISIS, as defined in Section 3.2 of [RFC8667].
The SR-Algorithm TLV is an optional TLV, when the originating router
does not advertise the SR-Algorithm TLV, it implies that algorithm 0
is the only algorithm supported by the router.
3. SRv6 Link Attribute TLVs
Based on [RFC9514] and [RFC9085], the following Link Attributes
SHOULD be supported in BGP-LS-SPF.
+======+=================================+===========+
| Type | Description | Reference |
+======+=================================+===========+
| 1106 | SRv6 End.X SID TLV | RFC 9514 |
+------+---------------------------------+-----------+
| 1106 | L2 Bundle Member Attributes TLV | RFC 9085 |
+------+---------------------------------+-----------+
| 267 | SRv6 Link MSD TLV | RFC 8814 |
+------+---------------------------------+-----------+
Table 2: Link Attribute TLVs for SRv6 with BGP-LS-SPF
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3.1. SRv6 End.X SID TLV
The SRv6 End.X SID TLV defined in [RFC9514] is used to advertise the
SRv6 SIDs associated with an IGP Adjacency SID behavior that
correspond to a point-to-point or point-to-multipoint link or
adjacency of the node running the IS-IS or OSPFv3 protocols. It is
also used by BGP-LS to advertise the BGP EPE Peer Adjacency SID for
SRv6 on the same lines as specified for SR-MPLS in [RFC9086].
BGP-LS-SPF SHOULD support this TLV to advertise the SRv6 SIDs
correspond to a point-to-point or adjacency of the node running the
BGP-LS-SPF.
3.2. L2 Bundele Member Attributes TLV
The L2 Bundle Member Attributes TLV is defined in [RFC9085], it
identifies an L2 Bundle Member link, which in turn is associated with
a parent L3 link. The TLV MAY include sub-TLVs that describe
attributes associated with the bundle member.
The network deployed BGP-LS-SPF may include trunk links. Therefore,
BGP-LS-SPF MAY support this TLV to advertise L2 bundle member link
attributes.
3.3. SRv6 Link MSD Types
The Link MSD TLV defined in [RFC8814] is used to advertise the limits
and the SRH operations supported on the specific link by the
SRv6-capable node. BGP-LS-SPF SHOULD support this TLV to advertise
the limits and operations supported on the specific link to enable
segment routing. The SRv6 MSD types specified in Section 4 of
[RFC9352] are also used with the BGP-LS-SPF Link MSD TLV.
The SRv6 Link MSD TLV is an optional TLV, for a specific MSD type, if
the advertised value is zero or no value is advertised, then the
headend can apply an SR Policy that only contains one segment without
inserting any SRH header.
4. SRv6 Prefix Attribute TLVs
Based on [RFC9514], the BGP-LS SRv6 Prefix Attributes only includes
the SRv6 Locator TLV. This TLV SHOULD be supported by BGP-LS-SPF.
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+======+==================+===========+
| Type | Description | Reference |
+======+==================+===========+
| 1162 | SRv6 Locator TLV | RFC 9514 |
+------+------------------+-----------+
Table 3: Prefix Attribute TLVs for
SRv6 with BGP-LS-SPF
4.1. SRv6 Locator TLV
The SRv6 Locator TLV defined in [RFC9514] is used to advertise the
locators supported by each node. Each locator is advertised in a
SRv6 Locator TLV. Locator is the key component of SRv6 SID, BGP-LS-
SPF SHOULD support this TLV to enable segment routing.
The flags fields of this TLV in BGP-LS-SPF is not used and MUST be
set to zero on transmission and MUST be ignored on receipt.
5. SRv6 SID NLRI
The SRv6 SID NLRI defined in [RFC9514] is used to carry the SRv6 SID
information. When SRv6 SIDs need to be advertised in BGP-SPF, the
following NLRI type and attributes TLV for SRv6 SID SHOULD be
supported in BGP-LS-SPF SAFI:
+======+============================+===========+
| Type | NLRI Type | Reference |
+======+============================+===========+
| 6 | SRv6 SID NLRI | RFC 9514 |
+------+----------------------------+-----------+
| 518 | SRv6 SID Information TLV | RFC 9514 |
+------+----------------------------+-----------+
| 1250 | SRv6 Endpoint Behavior TLV | RFC 9514 |
+------+----------------------------+-----------+
| 1252 | SRv6 SID Structure TLV | RFC 9514 |
+------+----------------------------+-----------+
Table 4: SRv6 SID NLRI with BGP-LS-SPF
The format of local node descriptors in this NLRI is consistent with
BGP-LS local node descriptors Section 5.2.1.2 of [RFC9552], which MAY
contain the Autonomous System and BGP-LS Identifier sub-TLV.
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5.1. SRv6 SID Information TLV
The SRv6 SID Information TLV is used to carry the SRv6 SID associated
with a node in a SRv6 SID NLRI. This TLV SHOULD be supported in BGP-
LS-SPF to advertise SRv6 SIDs.
5.2. SRv6 Endpoint Behavior TLV
The Endpoint Behavior TLV defined in [RFC9514] is a mandatory TLV
included in the BGP-LS Attribute, used to advertise the behaviors
associated with a SID. The BGP-LS-SPF SHOULD support this TLV to
enable advertisement of behaviors associated with a SRv6 SID.
5.3. SRv6 SID Structure TLV
The SRv6 SID Structure TLV defined in [RFC9514] is used to advertise
the length of each individual part of the SRv6 SID as defined in
[RFC8986]. It is an optional TLV in the BGP-LS Attribute for SRv6
SID NLRI and a sub-TLV of the SRv6 End.X SID. BGP-LS-SPF MAY support
this TLV to indicate the length of each individual part of the SRv6
SID of BGP-LS-SPF especially in some scenarios using compressed SID.
6. Operational Considerations
TBD
7. Security Considerations
This document introduces no additional security vulnerabilities in
addition to the ones as described in [RFC9552].
8. IANA Considerations
9. Acknowledgements
TBD
10. References
10.1. Normative References
[I-D.ietf-lsvr-bgp-spf]
Patel, K., Lindem, A., Zandi, S., and W. Henderickx, "BGP
Link-State Shortest Path First (SPF) Routing", Work in
Progress, Internet-Draft, draft-ietf-lsvr-bgp-spf-51, 23
January 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-lsvr-bgp-spf-51>.
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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>.
[RFC9552] Talaulikar, K., Ed., "Distribution of Link-State and
Traffic Engineering Information Using BGP", RFC 9552,
DOI 10.17487/RFC9552, December 2023,
<https://www.rfc-editor.org/info/rfc9552>.
[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>.
[RFC9514] Dawra, G., Filsfils, C., Talaulikar, K., Ed., Chen, M.,
Bernier, D., and B. Decraene, "Border Gateway Protocol -
Link State (BGP-LS) Extensions for Segment Routing over
IPv6 (SRv6)", RFC 9514, DOI 10.17487/RFC9514, December
2023, <https://www.rfc-editor.org/info/rfc9514>.
[RFC8814] Tantsura, J., Chunduri, U., Talaulikar, K., Mirsky, G.,
and N. Triantafillis, "Signaling Maximum SID Depth (MSD)
Using the Border Gateway Protocol - Link State", RFC 8814,
DOI 10.17487/RFC8814, August 2020,
<https://www.rfc-editor.org/info/rfc8814>.
[RFC9352] Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
and Z. Hu, "IS-IS Extensions to Support Segment Routing
over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
February 2023, <https://www.rfc-editor.org/info/rfc9352>.
[RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
H., and M. Chen, "Border Gateway Protocol - Link State
(BGP-LS) Extensions for Segment Routing", RFC 9085,
DOI 10.17487/RFC9085, August 2021,
<https://www.rfc-editor.org/info/rfc9085>.
10.2. Informative References
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[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
[RFC9086] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K.,
Ray, S., and J. Dong, "Border Gateway Protocol - Link
State (BGP-LS) Extensions for Segment Routing BGP Egress
Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August
2021, <https://www.rfc-editor.org/info/rfc9086>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
Authors' Addresses
Li Zhang
Huawei Technologies
No. 156 Beiqing Road
Beijing
China
Email: zhangli344@huawei.com
Jie Dong
Huawei Technologies
No. 156 Beiqing Road
Beijing
China
Email: jie.dong@huawei.com
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