Internet Engineering Task Force (IETF)
Request for Comments: 8510
Category: Standards Track
ISSN: 2070-1721
P. Psenak, Ed.
K. Talaulikar
Cisco Systems, Inc.
W. Henderickx
P. Pillay-Esnault
Huawei USA
January 2019

OSPF Link-Local Signaling (LLS) Extensions for

Local Interface ID Advertisement


Every OSPF interface is assigned an Interface ID that uniquely identifies the interface on the router. In some cases, it is useful to know the assigned Interface ID on the remote side of the adjacency (Remote Interface ID).

This document describes the extensions to OSPF link-local signaling (LLS) to advertise the Local Interface ID.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at

Copyright Notice

Copyright © 2019 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 ( in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
      1.1. Interface ID Exchange Using Link Local TE Opaque LSA .......4
      1.2. Requirements Language ......................................4
   2. Interface ID Exchange Using OSPF LLS ............................4
      2.1. Local Interface ID TLV .....................................5
   3. Backward Compatibility with RFC 4203 ............................5
   4. IANA Considerations .............................................6
   5. Security Considerations .........................................6
   6. References ......................................................6
      6.1. Normative References .......................................6
      6.2. Informative References .....................................7
   Acknowledgments ....................................................8
   Authors' Addresses .................................................8

1. Introduction

Every OSPF interface is assigned an Interface ID that uniquely identifies the interface on the router. [RFC2328] uses this Interface ID in the Router Link State Advertisement (Router-LSA) Link Data for unnumbered links and uses the value of the MIB-II ifIndex [RFC2863]. [RFC4203] refers to these Interface IDs as the Link Local/Remote Identifiers and defines a way to advertise and use them for GMPLS purposes. [RFC8379] defines a way to advertise Local/ Remote Interface IDs in the OSPFv2 Extended Link Opaque LSA.

There is a known OSPFv2 protocol problem in verifying the bidirectional connectivity with parallel unnumbered links. If there are two parallel unnumbered links between a pair of routers and each link is only advertised from a single direction, such two unidirectional parallel links could be considered as a valid single bidirectional link during the OSPF route computation on some other router. If each link is advertised with both its Local and Remote Interface IDs, the advertisement of each link from both sides of adjacency can be verified by cross-checking the Local and Remote Interface IDs of both advertisements.

From the perspective of the advertising router, the Local Interface ID is a known value. However, the Remote Interface ID needs to be learned before it can be advertised. [RFC4203] suggests using the TE Link Local LSA [RFC3630] to communicate the Local Interface ID to neighbors on the link. Though such a mechanism works, it has some drawbacks.

This document proposes an extension to OSPF link-local signaling (LLS) [RFC5613] to advertise the Local Interface ID.

1.1. Interface ID Exchange Using Link Local TE Opaque LSA

Usage of the Link Local TE Opaque LSA to propagate the Local Interface ID to the neighbors on the link is described in [RFC4203]. This mechanism has the following problems:

  • LSAs can only be flooded over an existing adjacency that is in Exchange state or greater. The adjacency state machine progresses independently on each side of the adjacency and, as such, may reach the Full state on one side before the Link Local TE Opaque LSA arrives. The consequence of this is that the link can be initially advertised without the Remote Interface ID. Later, when the Link Local TE Opaque LSA arrives, the link must be advertised again but this time with the valid Remote Interface ID. Implementations may choose to wait before advertising the link, but there is no guarantee that the neighbor will ever advertise the Link Local TE Opaque LSA with the Interface ID. In summary, the existing mechanism does not guarantee that the Remote Interface ID is known at the time the link is advertised.
  • The Link Local TE Opaque LSA is defined for MPLS Traffic Engineering, but the knowledge of the Remote Interface ID is useful also for cases where MPLS TE is not used. One example is the mentioned lack of a valid 2-way connectivity check for parallel point-to-point links between OSPF routers.

1.2. 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. Interface ID Exchange Using OSPF LLS

To address the problems described earlier and to allow the Interface ID exchange to be part of the neighbor discovery process, we propose to extend OSPF link-local signaling to advertise the Local Interface ID in OSPF Hello and Database Description (DD) packets.

2.1. Local Interface ID TLV

The Local Interface ID TLV is an LLS TLV. It 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            |
   |                   Local Interface ID                          |



  1. octets

Local Interface ID: The value of the Local Interface ID.

Local Interface ID TLV signaling using LLS is applicable to all OSPF interface types other than virtual links.

3. Backward Compatibility with RFC 4203

If the Local Interface ID signaling via the Link Local TE Opaque LSA is supported in addition to the new LLS mechanism, implementations that support Local Interface ID signaling using LLS MUST prefer the Local Interface ID value received through LLS over the value received through the Link Local TE Opaque LSA if both are received from the same OSPF router.

Implementations that support Local Interface ID signaling via the Link Local TE Opaque LSA MAY continue to do so to ensure backward compatibility. If they also support Local Interface ID signaling using LLS as described in the document, they MUST signal the same Local Interface ID via both mechanisms.

During the rare conditions in which the Local Interface ID changes, a timing interval may exist where the received values of the Local Interface ID advertised through LLS and the Link Local TE Opaque LSA may differ. Such a situation is temporary, and received values via both mechanisms should become equal as soon as the next Hello and/or Link Local TE Opaque LSA is regenerated by the originator.

4. IANA Considerations

IANA has allocated the following code point in the "Link Local Signalling TLV Identifiers (LLS Types)" subregistry of the "Open Shortest Path First (OSPF) Link Local Signalling (LLS) - Type/Length/ Value Identifiers (TLV)" registry.

  1. - Local Interface ID TLV

5. Security Considerations

The security considerations for "OSPF Link-Local Signaling" [RFC5613] also apply to the Local Interface ID TLV described in this document. The current usage of a neighbor's Local Interface ID is to disambiguate parallel links between OSPF routers. Hence, modification of the advertised Local Interface ID TLV may result in the wrong neighbor Interface ID being advertised in the OSPFv2 Extended Link Opaque LSA [RFC7684] and could prevent the link from being used. If authentication is being used in the OSPF routing domain [RFC5709][RFC7474], then the Cryptographic Authentication TLV [RFC5613] SHOULD also be used to protect the contents of the LLS block.

Receiving a malformed LLS Local Interface ID TLV MUST NOT result in a hard router or OSPF process failure. The reception of malformed LLS TLVs or sub-TLVs SHOULD be logged, but such logging MUST be rate- limited to prevent denial-of-service (DoS) attacks.

The Interface ID is assigned by the advertising OSPF router as a locally unique identifier and need not be unique in any broader context; it is not expected to contain any information about the device owner or traffic transiting the device, so there are no privacy concerns associated with its advertisement.

6. References

6.1. 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,
   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
   [RFC4203]  Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
              Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
   [RFC5613]  Zinin, A., Roy, A., Nguyen, L., Friedman, B., and
              D. Yeung, "OSPF Link-Local Signaling", RFC 5613,
              DOI 10.17487/RFC5613, August 2009,
   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <>.
   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.
   [RFC8379]  Hegde, S., Sarkar, P., Gredler, H., Nanduri, M., and
              L. Jalil, "OSPF Graceful Link Shutdown", RFC 8379,
              DOI 10.17487/RFC8379, May 2018,

6.2. Informative References

   [RFC2863]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group
              MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,
   [RFC5709]  Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
              Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
              Authentication", RFC 5709, DOI 10.17487/RFC5709, October
              2009, <>.
   [RFC7474]  Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
              "Security Extension for OSPFv2 When Using Manual Key
              Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,


Thanks to Tony Przygienda for his extensive review and useful comments.

Authors' Addresses

   Peter Psenak (editor)
   Cisco Systems, Inc.
   Apollo Business Center
   Mlynske nivy 43
   Bratislava  821 09


   Ketan Talaulikar
   Cisco Systems, Inc.
   S.No. 154/6, Phase I, Hinjawadi
   Pune, Maharashtra  411 057


   Wim Henderickx
   Copernicuslaan 50
   Antwerp  2018
   Padma Pillay-Esnault
   Huawei USA
   2330 Central Expressway
   Santa Clara,  CA 95050
   United States of America