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Versions: 00                                                            
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
   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 August 26, 2021.

Copyright Notice

   Copyright (c) 2021 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
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   (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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   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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