Internet-Draft BGP-LS Extensions for IS-IS FR February 2024
Head & Przygienda Expires 12 August 2024 [Page]
Inter-Domain Routing
Intended Status:
J. Head, Ed.
Juniper Networks
T. Przygienda
Juniper Networks

BGP-LS Extensions for IS-IS Flood Reflection


IS-IS Flood Reflection is a mechanism that allows flat, single-area IS-IS topologies to scale beyond their traditional limitations.

This document defines new BGP-LS (BGP Link-State) TLVs in order to carry IS-IS Flood Reflection information.

Status of This Memo

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This Internet-Draft will expire on 12 August 2024.

Table of Contents

1. Introduction

IS-IS Flood Reflection [RFC9377] is a mechanism that allows flat, single-area IS-IS topologies to scale beyond their existing limitations.

Flood Reflection topologies are broken into clusters. The participating nodes must convey their unique Cluster ID signifying their membership in a particular topology as well as their role (e.g. Flood Reflector or Client).

BGP Link-State RFC9552 [RFC9552] defines mechanisms to advertise information about the underlying IGP in BGP NLRI to an external entity (e.g. a controller). A new BGP-LS TLV is required in order to describe IS-IS Flood Reflection node and link details. This document defines that TLV.

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. BGP-LS Extensions for IS-IS Flood Reflection

Controllers may need to compute traffic engineered paths across Flood Reflection clusters. This requires that they be aware of Flood Reflection information (be it operational or configured), such as Cluster ID, C-bit (which indicates Flood Reflector or Client), and any applicable sub-TLVs.

The IS-IS Flood Reflection TLV can be advertised in BGP-LS as either a Node attribute or a Link attribute. When describing a node, values are derived from the IS-IS Flood Reflection Discovery Sub-TLV. When describing a link, values are derived from the IS-IS Adjacency Sub-TLV. The semantics of any fields within the TLV/sub-TLVs are described in [RFC9377].

This document defines the following BGP-LS TLVs for use with IS-IS Flood Reflection.

 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            |
|                  Flood Reflection Cluster ID                  |
|                          Sub-TLVs ...                         |
Figure 1: IS-IS Flood Reflection TLV

2.1. IS-IS Flood Reflection TLV

This section defines a BGP-LS Attribute that corresponds to IS-IS Flood Reflection TLVs/sub-TLVs as described in [RFC9377]


3. Design Considerations

It is typical that a BGP-LS extension mirror all of the corresponding IGP components (i.e. TLVs, sub-TLVs, and sub-sub-TLVs) in order to carry the necessary IGP information. IS-IS Flood Reflection [RFC9377] describes "Tunnel-Based" deployments where an optional "Flood Reflection Discovery Tunnel Type Sub-Sub-TLV" is used to facilitate the creation of "L1 Shortcuts" (i.e. tunnels) between nodes in a Flood Reflection cluster. In this document, it is RECOMMENDED that this sub-sub-TLV be excluded from the BGP-LS extension for the following reasons.

For example, shortcuts could be point-to-point IS-IS tunnels or be encapsulated by other means. In deployments where the tunnels are IS-IS based, no additional BGP-LS extension is required as the existing BGP-LS extensions for IS-IS will suffice.

However, for deployments where tunnels are encapsulated by other means it is not desirable for BGP-LS to carry that information as it is tunnel information and not IGP information. Other existing or new BGP-LS extensions that correspond to the particular tunnel type SHOULD be used to fulfill any BGP-LS requirements.

An implementation MAY still choose to include the "Flood Reflection Discovery Tunnel Type Sub-Sub-TLV" for the sake of completeness. For example, it might be beneficial for cases where BGP-LS is the only way this information can be obtained.

4. IANA Considerations

This section requests the following values from the "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" registry for the following TLVs:

4.1. Requested TLV Entries

Table 1: Requested TLV Entries
TLV Code Point Description IS-IS TLV/Sub-TLV Reference
1160 IS-IS Flood Reflection (22|23|25|141|222|223|242)/161 This document.

5. Security Considerations

Procedures and protocol extensions defined in this document do not affect the BGP security model. See the "Security Considerations" section of [RFC4271] for a discussion of BGP security. Also, refer to [RFC4272] and [RFC6952] for analyses of BGP security issues. Security considerations for acquiring and distributing BGP-LS information are discussed in [RFC9552].

The TLVs introduced in this document are used to propagate IS-IS Flood Reflection TLVs defined in [RFC9377]. These TLVs represent IS-IS Flood Reflection state and are therefore assumed to support any/all of the required security and authentication mechanisms as described in [RFC9377] to prevent any security issues when propagating the TLVs into BGP-LS.

6. Acknowledgements

The authors would like to thank Ketan Talaulikar for several iterations of review and practical suggestions.

7. References

7.1. Normative References

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", , <>.
Murphy, S., "BGP Security Vulnerabilities Analysis", , <>.
Jethanandani, M., Patel, K., and L. Zheng, "Analysis of BGP, LDP, PCEP, and MSDP Issues According to the Keying and Authentication for Routing Protocols (KARP) Design Guide", , <>.
Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Przygienda, T., Ed., Bowers, C., Lee, Y., Sharma, A., and R. White, "IS-IS Flood Reflection", RFC 9377, DOI 10.17487/RFC9377, , <>.
Talaulikar, K., "Distribution of Link-State and Traffic Engineering Information Using BGP", , <>.

Authors' Addresses

Jordan Head (editor)
Juniper Networks
1137 Innovation Way
Sunnyvale, CA
United States of America
Tony Przygienda
Juniper Networks
1137 Innovation Way
Sunnyvale, CA
United States of America