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IETF RFC 8510
Last modified on Friday, January 25th, 2019
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Internet Engineering Task Force (IETF) P. Psenak, Ed.
Request for Comments: 8510 K. Talaulikar
Category: Standards Track Cisco Systems, Inc.
ISSN: 2070-1721 W. Henderickx
Nokia
P. Pillay-Esnault
Huawei USA
January 2019
OSPF Link-Local Signaling (LLS) Extensions for
Local Interface ID Advertisement
 Abstract
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
https://www.rfc-editor.org/info/RFC 8510.
Psenak, et al. Standards Track PAGE 1 
RFC 8510 OSPF LLS Extensions for Interface ID January 2019
Copyright Notice
Copyright (c) 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
(https://trustee.ietf.org/license-info) 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
Psenak, et al. Standards Track PAGE 2
RFC 8510 OSPF LLS Extensions for Interface ID January 2019
1. Introduction
Every OSPF interface is assigned an Interface ID that uniquely
identifies the interface on the router. [RFC 2328] 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
[RFC 2863]. [RFC 4203] refers to these Interface IDs as the Link
Local/Remote Identifiers and defines a way to advertise and use them
for GMPLS purposes. [RFC 8379] 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. [RFC 4203] suggests using the TE
Link Local LSA [RFC 3630] 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) [RFC 5613] to advertise the Local Interface ID.
Psenak, et al. Standards Track PAGE 3
RFC 8510 OSPF LLS Extensions for Interface ID January 2019
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 [RFC 4203].
This mechanism has the following problems:
o 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.
o 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 [RFC 2119] [RFC 8174] 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.
Psenak, et al. Standards Track PAGE 4
RFC 8510 OSPF LLS Extensions for Interface ID January 2019
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 18
Length: 4 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.
Psenak, et al. Standards Track PAGE 5
RFC 8510 OSPF LLS Extensions for Interface ID January 2019
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.
18 - Local Interface ID TLV
5. Security Considerations
The security considerations for "OSPF Link-Local Signaling" [RFC 5613]
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 [RFC 7684] and could prevent the link from
being used. If authentication is being used in the OSPF routing
domain [RFC 5709][RFC 7474], then the Cryptographic Authentication TLV
[RFC 5613] 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
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<https://www.rfc-editor.org/info/RFC 2119>.
[RFC 2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC 2328, April 1998,
<https://www.rfc-editor.org/info/RFC 2328>.
Psenak, et al. Standards Track PAGE 6
RFC 8510 OSPF LLS Extensions for Interface ID January 2019
[RFC 3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC 3630, September 2003,
<https://www.rfc-editor.org/info/RFC 3630>.
[RFC 4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, DOI 10.17487/RFC 4203, October 2005,
<https://www.rfc-editor.org/info/RFC 4203>.
[RFC 5613] Zinin, A., Roy, A., Nguyen, L., Friedman, B., and
D. Yeung, "OSPF Link-Local Signaling", RFC 5613,
DOI 10.17487/RFC 5613, August 2009,
<https://www.rfc-editor.org/info/RFC 5613>.
[RFC 7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC 7684, November
2015, <https://www.rfc-editor.org/info/RFC 7684>.
[RFC 8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC 8174,
May 2017, <https://www.rfc-editor.org/info/RFC 8174>.
[RFC 8379] Hegde, S., Sarkar, P., Gredler, H., Nanduri, M., and
L. Jalil, "OSPF Graceful Link Shutdown", RFC 8379,
DOI 10.17487/RFC 8379, May 2018,
<https://www.rfc-editor.org/info/RFC 8379>.
6.2. Informative References
[RFC 2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, DOI 10.17487/RFC 2863, June 2000,
<https://www.rfc-editor.org/info/RFC 2863>.
[RFC 5709] 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/RFC 5709, October
2009, <https://www.rfc-editor.org/info/RFC 5709>.
[RFC 7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
"Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, DOI 10.17487/RFC 7474, April 2015,
<https://www.rfc-editor.org/info/RFC 7474>.
Psenak, et al. Standards Track PAGE 7
RFC 8510 OSPF LLS Extensions for Interface ID January 2019
Acknowledgments
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
Slovakia
Email: ppsenak@cisco.com
Ketan Talaulikar
Cisco Systems, Inc.
S.No. 154/6, Phase I, Hinjawadi
Pune, Maharashtra 411 057
India
Email: ketant@cisco.com
Wim Henderickx
Nokia
Copernicuslaan 50
Antwerp 2018
Belgium
Email: wim.henderickx@nokia.com
Padma Pillay-Esnault
Huawei USA
2330 Central Expressway
Santa Clara, CA 95050
United States of America
Email: padma@huawei.com
Psenak, et al. Standards Track PAGE 8
RFC TOTAL SIZE: 15304 bytes
PUBLICATION DATE: Friday, January 25th, 2019
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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