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Przygienda 4 Updates: 8401,8444 (if approved) Juniper Networks 5 Intended status: Standards Track A. Dolganow 6 Expires: November 30, 2019 H. Bidgoli 7 Nokia 8 I. Wijnands 9 Cisco Systems 10 A. Gulko 11 Thomson Reuters 12 May 29, 2019 14 BIER Underlay Path Calculation Algorithm and Constraints 15 draft-ietf-bier-bar-ipa-04 17 Abstract 19 This document specifies general rules for interaction between the BAR 20 (BIER Algorithm) and IPA (IGP Algorithm) fields defined in ISIS/ 21 OSPFv2 Extensions for BIER. The semantics for the BAR and IPA fields 22 (when both or any of them is non-zero) defined in this document 23 updates the semantics defined in RFC8444/RFC8401. 25 Requirements Language 27 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 28 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 29 document are to be interpreted as described in RFC2119. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at https://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on November 30, 2019. 48 Copyright Notice 50 Copyright (c) 2019 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (https://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 66 2. General Rules for the BAR and IPA fields . . . . . . . . . . 3 67 2.1. When BAR Is Not Used . . . . . . . . . . . . . . . . . . 4 68 2.2. Exceptions/Extensions to the General Rules . . . . . . . 4 69 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 70 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 71 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 72 5.1. Normative References . . . . . . . . . . . . . . . . . . 4 73 5.2. Informative References . . . . . . . . . . . . . . . . . 5 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 76 1. Introduction 78 In Bit Index Explicit Replication (BIER) architecture [RFC8279], 79 packets with a BIER encapsulation header are forwarded to the 80 neighbors on the underlay paths towards the BFERs. For each sub- 81 domain, the paths are calculated in the underlay topology for the 82 sub-domain, following a calculation algorithm specific to the sub- 83 domain. The could be congruent or incongruent 84 with unicast. The topology could be a default topology, a multi- 85 topology [RFC5120] topology. The algorithm could be a generic IGP 86 algorithm (e.g. SPF) or could be a BIER specific one defined in the 87 future. 89 In [RFC8401] and [RFC8444], an 8-bit BAR (BIER Algorithm) field and 90 8-bit IPA (IGP Algorithm) field are defined to signal the BIER 91 specific algorithm and generic IGP Algorithm respectively and only 92 value 0 is allowed for both fields in those two documents. This 93 document specifies the general rules for the two fields and their 94 interaction when either or both fields are not 0, and updates their 95 semantics defined in [RFC8444] and [RFC8401]. 97 2. General Rules for the BAR and IPA fields 99 For a particular sub-domain, all routers SHOULD be provisioned with 100 and signal the same BAR and IPA values. When a BFR discovers another 101 BFR advertising different BAR or IPA value from its own provisioned, 102 it MUST treat the advertising BFR as incapable of supporting BIER for 103 the sub-domain. How incapable routers are handled is outside the 104 scope of this document. 106 It is expected that both the BAR and IPA values could have both 107 algorithm and constraints semantics. To generalize, we introduce the 108 following terms: 110 o BC: BIER-specific Constraints 112 o BA: BIER-specific Algorithm 114 o RC: Generic Routing Constraints 116 o RA: Generic Routing Algorithm 118 o BCBA: BC + BA 120 o RCRA: RC + RA 122 A BAR value corresponds to a BCBA, and a IPA value corresponds to a 123 RCRA. Any of the RC/BC/BA could be "NULL", which means there are no 124 corresponding constraints or algorithm. 126 When a new BAR value is defined, its corresponding BC/BA semantics 127 MUST be specified. For a new IGP Algorithm to be used as a BIER IPA, 128 its RC/RA semantics MUST also be clear. 130 For a particular topology X (which could be a default topology or 131 multi-topolgy topology) that a sub-domain is associated with, a 132 router calculates the underlay paths according to its provisioned 133 BCBA and RCRA the following way: 135 1. Apply the BIER constraints, resulting in BC(X). 137 2. Apply the routing constraints, resulting in RC(BC(X)). 139 3. Select the algorithm AG as following: 141 A. If BA is NULL, AG is set to RA. 143 B. If BA is not NULL, AG is set to BA. 145 4. Run AG on RC(BC(X)). 147 2.1. When BAR Is Not Used 149 The BIER Algorithm registry established by [RFC8401] and also used in 150 [RFC8444] has value 0 for "No BIER specific algorithm is used". That 151 translates to NULL BA and NULL BC. Following the rules defined 152 above, the IPA value alone identifies the calculation algorithm and 153 constraints to be used for a particular sub-domain when BAR is 0. 155 2.2. Exceptions/Extensions to the General Rules 157 Exceptions or extensions to the above general rules may be specified 158 in the future for specific BAR and/or IPA values. When that happens, 159 compatibility with defined BAR and/or IPA values and semantics need 160 to be specified. 162 3. IANA Considerations 164 No IANA Consideration is requested in this document. 166 4. Acknowledgements 168 The authors thanks Alia Atlas, Eric Rosen, Senthil Dhanaraj and many 169 others for their suggestions and comments. In particular, the BCBA/ 170 RCRA representation for the interaction rules is based on Alia's 171 write-up. 173 5. References 175 5.1. Normative References 177 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 178 Requirement Levels", BCP 14, RFC 2119, 179 DOI 10.17487/RFC2119, March 1997, 180 . 182 [RFC8401] Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z. 183 Zhang, "Bit Index Explicit Replication (BIER) Support via 184 IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018, 185 . 187 [RFC8444] Psenak, P., Ed., Kumar, N., Wijnands, IJ., Dolganow, A., 188 Przygienda, T., Zhang, J., and S. Aldrin, "OSPFv2 189 Extensions for Bit Index Explicit Replication (BIER)", 190 RFC 8444, DOI 10.17487/RFC8444, November 2018, 191 . 193 5.2. Informative References 195 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 196 Topology (MT) Routing in Intermediate System to 197 Intermediate Systems (IS-ISs)", RFC 5120, 198 DOI 10.17487/RFC5120, February 2008, 199 . 201 [RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A., 202 Przygienda, T., and S. Aldrin, "Multicast Using Bit Index 203 Explicit Replication (BIER)", RFC 8279, 204 DOI 10.17487/RFC8279, November 2017, 205 . 207 Authors' Addresses 209 Zhaohui Zhang 210 Juniper Networks 212 EMail: zzhang@juniper.net 214 Antoni Przygienda 215 Juniper Networks 217 EMail: prz@juniper.net 219 Andrew Dolganow 220 Nokia 222 EMail: andrew.dolganow@nokia.com 224 Hooman Bidgoli 225 Nokia 227 EMail: hooman.bidgoli@nokia.com 229 IJsbrand Wijnands 230 Cisco Systems 232 EMail: ice@cisco.com 233 Arkadiy Gulko 234 Thomson Reuters 236 EMail: arkadiy.gulko@thomsonreuters.com