Internet DRAFT - draft-bowers-lsr-isis-gen-info-clarifications
draft-bowers-lsr-isis-gen-info-clarifications
LSR C. Bowers
Internet-Draft Juniper Networks Inc.
Intended status: Standards Track February 22, 2021
Expires: August 26, 2021
Clarification of the Use of the IS-IS Generic Information TLV
draft-bowers-lsr-isis-gen-info-clarifications-00
Abstract
This document clarifies some aspects of [RFC6823], "Advertising
Generic Information in IS-IS".
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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
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This Internet-Draft will expire on August 26, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Associating Information Carried in GENINFO TLVs with
Information Carried in Other IS-IS Advertisements . . . . . . 2
3. Associating Information Carried in GENINFO TLVs with
Information Carried in Other IS-IS Instances . . . . . . . . 3
4. Congruent and Incongruent Instances . . . . . . . . . . . . . 3
5. Leaking the GENINFO TLV . . . . . . . . . . . . . . . . . . . 3
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
9. Normative References . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
[RFC6823] defines the Generic Information TLV for carrying non-
routing information in IS-IS. The current document clarifies some
aspects of [RFC6823].
2. Associating Information Carried in GENINFO TLVs with Information
Carried in Other IS-IS Advertisements
In order to avoid duplicating information sent in IS-IS
advertisements, it is useful for an application to be able to
associate information carried in application-specific GENINFO APPsub-
TLVs with the underlying objects being described by other IS-IS
advertisements. This is allowed as long as the requirements of
Section 6 of [RFC6823] are met.
As an example, an application may need to learn the latency of a
particular link using the existing Unidirectional Link Delay sub-
TLV(#33) carried in TLV#22, while at the same time using an
application-specific GENINFO APPsub-TLV to distribute application-
specific information about the same link. If the APPsub-TLV carries
the System ID of the neighbor together with an interface identifier,
and the TLV#22 that carries the Unidirectional Link Delay sub-TLV
also carries an interface identifer, then the application can
uniquely identify the underlying link being described by the two
advertisements.
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A document that specifies how an application-specific GENINFO TLV is
used should also specify how associations of information in different
advertisements should be made.
3. Associating Information Carried in GENINFO TLVs with Information
Carried in Other IS-IS Instances
[RFC8202] specifies a mechanism for multiple IS-IS protocol instances
to share the same circuit by including the IID-TLV in the PDUs
associated with a particular IS-IS protocol instance. GENINFO TLVs
can be carried in different IS-IS instances. When an application
associates information carried in GENINFO TLVs with information
carried in other IS-IS advertisements, it may be useful for the
application to take into account the particular IS-IS instance in
which those other IS-IS advertisements appear.
As an example, in a particular network some links participate in
three different IS-IS instances. PDUs with IID=50 and IID=60
correspond to two different IS-IS routing protocol instances, each
with an independent IS-IS adjacency establishment, Update process,
and Decision process. PDUs with IID=70 correspond to an IS-IS
instance dedicated to carrying the GENINFO TLVs for a particular
application. This application-specific IS-IS instance has an
independent IS-IS adjacency establishment and Update process, but
does not implement the IS-IS Decision process. The network operator
intends that the application should use the latency advertised using
TLV#22/sub-TLV#33 in the IS-IS instance with IID=60. This can be
accomplished using configuration or other mechanisms.
A document that specifies how an application-specific GENINFO TLV is
used should also specify how associations of information in different
advertisements should be made when multiple IS-IS instances are used.
4. Congruent and Incongruent Instances
Neither [RFC8202] nor [RFC6823] places any requirements on the use of
congruent or incongruent IS-IS instances when multiple IS-IS
instances are used. In the example described in Section 3, the three
IS-IS instances may be congruent with one another (that is, use the
same set of links on which to form adjacencies) or not.
5. Leaking the GENINFO TLV
Section 4.1 of [RFC6823] contains the following requirement.
In order to prevent the use of stale GENINFO information, a system
MUST NOT use a GENINFO TLV present in an LSP of a system that is not
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currently reachable via Level-x paths, where "x" is the level (1 or
2) associated with the LSP in which the GENINFO TLV appears.
The above requirement does not provide an unambiguous specification
for determining the reachability of a system originating a GENINFO
TLV when multiple IS-IS instances are present.
The current document clarifies the requirement of Section 4.1 of
[RFC6823] in the following manner. A document that specifies how an
application-specific GENINFO TLV is to be leaked should also specify
the means by which the leaking of stale GENINFO information is to be
prevented.
6. Security Considerations
TBD
7. IANA Considerations
TBD
8. Acknowledgements
TBD
9. 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>.
[RFC6823] Ginsberg, L., Previdi, S., and M. Shand, "Advertising
Generic Information in IS-IS", RFC 6823,
DOI 10.17487/RFC6823, December 2012,
<https://www.rfc-editor.org/info/rfc6823>.
[RFC8202] Ginsberg, L., Previdi, S., and W. Henderickx, "IS-IS
Multi-Instance", RFC 8202, DOI 10.17487/RFC8202, June
2017, <https://www.rfc-editor.org/info/rfc8202>.
Author's Address
Chris Bowers
Juniper Networks Inc.
Email: cbowers@juniper.net
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