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Bowers 3 Internet-Draft Juniper Networks Inc. 4 Intended status: Standards Track February 22, 2021 5 Expires: August 26, 2021 7 Clarification of the Use of the IS-IS Generic Information TLV 8 draft-bowers-lsr-isis-gen-info-clarifications-00 10 Abstract 12 This document clarifies some aspects of [RFC6823], "Advertising 13 Generic Information in IS-IS". 15 Requirements Language 17 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 18 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 19 document are to be interpreted as described in RFC 2119 [RFC2119]. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on August 26, 2021. 38 Copyright Notice 40 Copyright (c) 2021 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (https://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Associating Information Carried in GENINFO TLVs with 57 Information Carried in Other IS-IS Advertisements . . . . . . 2 58 3. Associating Information Carried in GENINFO TLVs with 59 Information Carried in Other IS-IS Instances . . . . . . . . 3 60 4. Congruent and Incongruent Instances . . . . . . . . . . . . . 3 61 5. Leaking the GENINFO TLV . . . . . . . . . . . . . . . . . . . 3 62 6. Security Considerations . . . . . . . . . . . . . . . . . . . 4 63 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 64 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 65 9. Normative References . . . . . . . . . . . . . . . . . . . . 4 66 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4 68 1. Introduction 70 [RFC6823] defines the Generic Information TLV for carrying non- 71 routing information in IS-IS. The current document clarifies some 72 aspects of [RFC6823]. 74 2. Associating Information Carried in GENINFO TLVs with Information 75 Carried in Other IS-IS Advertisements 77 In order to avoid duplicating information sent in IS-IS 78 advertisements, it is useful for an application to be able to 79 associate information carried in application-specific GENINFO APPsub- 80 TLVs with the underlying objects being described by other IS-IS 81 advertisements. This is allowed as long as the requirements of 82 Section 6 of [RFC6823] are met. 84 As an example, an application may need to learn the latency of a 85 particular link using the existing Unidirectional Link Delay sub- 86 TLV(#33) carried in TLV#22, while at the same time using an 87 application-specific GENINFO APPsub-TLV to distribute application- 88 specific information about the same link. If the APPsub-TLV carries 89 the System ID of the neighbor together with an interface identifier, 90 and the TLV#22 that carries the Unidirectional Link Delay sub-TLV 91 also carries an interface identifer, then the application can 92 uniquely identify the underlying link being described by the two 93 advertisements. 95 A document that specifies how an application-specific GENINFO TLV is 96 used should also specify how associations of information in different 97 advertisements should be made. 99 3. Associating Information Carried in GENINFO TLVs with Information 100 Carried in Other IS-IS Instances 102 [RFC8202] specifies a mechanism for multiple IS-IS protocol instances 103 to share the same circuit by including the IID-TLV in the PDUs 104 associated with a particular IS-IS protocol instance. GENINFO TLVs 105 can be carried in different IS-IS instances. When an application 106 associates information carried in GENINFO TLVs with information 107 carried in other IS-IS advertisements, it may be useful for the 108 application to take into account the particular IS-IS instance in 109 which those other IS-IS advertisements appear. 111 As an example, in a particular network some links participate in 112 three different IS-IS instances. PDUs with IID=50 and IID=60 113 correspond to two different IS-IS routing protocol instances, each 114 with an independent IS-IS adjacency establishment, Update process, 115 and Decision process. PDUs with IID=70 correspond to an IS-IS 116 instance dedicated to carrying the GENINFO TLVs for a particular 117 application. This application-specific IS-IS instance has an 118 independent IS-IS adjacency establishment and Update process, but 119 does not implement the IS-IS Decision process. The network operator 120 intends that the application should use the latency advertised using 121 TLV#22/sub-TLV#33 in the IS-IS instance with IID=60. This can be 122 accomplished using configuration or other mechanisms. 124 A document that specifies how an application-specific GENINFO TLV is 125 used should also specify how associations of information in different 126 advertisements should be made when multiple IS-IS instances are used. 128 4. Congruent and Incongruent Instances 130 Neither [RFC8202] nor [RFC6823] places any requirements on the use of 131 congruent or incongruent IS-IS instances when multiple IS-IS 132 instances are used. In the example described in Section 3, the three 133 IS-IS instances may be congruent with one another (that is, use the 134 same set of links on which to form adjacencies) or not. 136 5. Leaking the GENINFO TLV 138 Section 4.1 of [RFC6823] contains the following requirement. 140 In order to prevent the use of stale GENINFO information, a system 141 MUST NOT use a GENINFO TLV present in an LSP of a system that is not 142 currently reachable via Level-x paths, where "x" is the level (1 or 143 2) associated with the LSP in which the GENINFO TLV appears. 145 The above requirement does not provide an unambiguous specification 146 for determining the reachability of a system originating a GENINFO 147 TLV when multiple IS-IS instances are present. 149 The current document clarifies the requirement of Section 4.1 of 150 [RFC6823] in the following manner. A document that specifies how an 151 application-specific GENINFO TLV is to be leaked should also specify 152 the means by which the leaking of stale GENINFO information is to be 153 prevented. 155 6. Security Considerations 157 TBD 159 7. IANA Considerations 161 TBD 163 8. Acknowledgements 165 TBD 167 9. Normative References 169 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 170 Requirement Levels", BCP 14, RFC 2119, 171 DOI 10.17487/RFC2119, March 1997, 172 . 174 [RFC6823] Ginsberg, L., Previdi, S., and M. Shand, "Advertising 175 Generic Information in IS-IS", RFC 6823, 176 DOI 10.17487/RFC6823, December 2012, 177 . 179 [RFC8202] Ginsberg, L., Previdi, S., and W. Henderickx, "IS-IS 180 Multi-Instance", RFC 8202, DOI 10.17487/RFC8202, June 181 2017, . 183 Author's Address 185 Chris Bowers 186 Juniper Networks Inc. 188 Email: cbowers@juniper.net