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Zhang 3 Internet-Draft A. Przygienda 4 Updates: 8401,8444 (if approved) Juniper Networks 5 Intended status: Standards Track A. Dolganow 6 Expires: April 2, 2022 Individual 7 H. Bidgoli 8 Nokia 9 I. Wijnands 10 Individual 11 A. Gulko 12 Edward Jones Wealth Management 13 September 29, 2021 15 BIER Underlay Path Calculation Algorithm and Constraints 16 draft-ietf-bier-bar-ipa-08 18 Abstract 20 This document specifies general rules for the interaction between the 21 BIER Algorithm (BAR) and the IGP Algorithm (IPA) used for underlay 22 path calculation. The semantics defined in this document update 23 RFC8401, RFC8444, and draft-ietf-bier-ospfv3-extensions. 25 Requirements Language 27 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 28 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 29 "OPTIONAL" in this document are to be interpreted as described in BCP 30 14 [RFC2119] [RFC8174] when, and only when, they appear in all 31 capitals, as shown here. 33 Status of This Memo 35 This Internet-Draft is submitted in full conformance with the 36 provisions of BCP 78 and BCP 79. 38 Internet-Drafts are working documents of the Internet Engineering 39 Task Force (IETF). Note that other groups may also distribute 40 working documents as Internet-Drafts. The list of current Internet- 41 Drafts is at https://datatracker.ietf.org/drafts/current/. 43 Internet-Drafts are draft documents valid for a maximum of six months 44 and may be updated, replaced, or obsoleted by other documents at any 45 time. It is inappropriate to use Internet-Drafts as reference 46 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on April 2, 2022. 50 Copyright Notice 52 Copyright (c) 2021 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (https://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 68 2. General Rules for the BAR and IPA fields . . . . . . . . . . 3 69 2.1. When BAR Is Not Used . . . . . . . . . . . . . . . . . . 4 70 2.2. Exceptions/Extensions to the General Rules . . . . . . . 4 71 3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4 72 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 73 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 74 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 75 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 76 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 77 7.2. Informative References . . . . . . . . . . . . . . . . . 5 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 80 1. Introduction 82 In the Bit Index Explicit Replication (BIER) architecture [RFC8279], 83 packets with a BIER encapsulation header are forwarded to the 84 neighbors on the underlay paths towards the BFERs. The paths are 85 calculated in the underlay topology for each sub-domain following a 86 calculation algorithm specific to the sub-domain. The topology or 87 algorithm may be congruent with unicast. The algorithm could be a 88 generic IGP algorithm (e.g. SPF) or could be a BIER specific one 89 defined in the future. 91 This document specifies general rules for the interaction between the 92 BIER Algorithm (BAR) and the IGP Algorithm (IPA) used for underlay 93 path calculation. The semantics defined in this document update 94 [RFC8401], [RFC8444], and [I-D.ietf-bier-ospfv3-extensions]. 96 2. General Rules for the BAR and IPA fields 98 For a particular sub-domain, all BIER Forwarding Routers (BFRs) MUST 99 be provisioned with and signal the same BAR and IPA values. If a BFR 100 discovers another BFR advertising different BAR or IPA value, it MUST 101 treat the advertising router as incapable of supporting BIER (one way 102 of handling incapable routers is documented in Section 6.9 of 103 [RFC8279] and additional methods may be defined in the future). 105 Both BAR and IPA have both algorithm and constraints semantics. To 106 generalize, we introduce the following terms: 108 o BC: BIER-specific Constraints 110 o BA: BIER-specific Algorithm 112 o RC: Generic Routing Constraints 114 o RA: Generic Routing Algorithm 116 o BCBA: BC + BA 118 o RCRA: RC + RA 120 A BAR value corresponds to a BCBA, and an IPA value corresponds to an 121 RCRA. Any of the RC/BC/BA could be "NULL", which means there are no 122 corresponding constraints or algorithm. 124 When a new BAR value is defined, its corresponding BC/BA semantics 125 MUST be specified. For a new IGP Algorithm to be used as a BIER IPA, 126 its RC/RA semantics MUST also be clearly specified. 128 For a particular topology X (which could be a default topology or 129 non-default topology) that a sub-domain is associated with, a router 130 calculates the underlay paths according to its provisioned BCBA and 131 RCRA the following way: 133 1. Apply the BIER constraints, resulting in BC(X). 135 2. Apply the routing constraints, resulting in RC(BC(X)). 137 3. Select the algorithm AG as following: 139 A. If BA is NULL, AG is set to RA. 141 B. If BA is not NULL, AG is set to BA. 143 4. Run AG on RC(BC(X)). 145 2.1. When BAR Is Not Used 147 The BIER Algorithm registry established by [RFC8401] and also used in 148 [RFC8444] has value 0 for "No BIER specific algorithm is used". That 149 translates to NULL BA and NULL BC. Following the rules defined 150 above, the IPA value alone identifies the calculation algorithm and 151 constraints to be used for a particular sub-domain when BAR is 0. 153 2.2. Exceptions/Extensions to the General Rules 155 Exceptions or extensions to the above general rules may be specified 156 in the future for specific BAR and/or IPA values. When that happens, 157 compatibility with defined BAR and/or IPA values and semantics need 158 to be specified. 160 3. Examples 162 As an example, one may define BAR=x with the semantics of "excluding 163 BIER incapable routers". That BIER specific constraint can go with 164 any IPA: whatever RCRA defined by the IPA is augmented with 165 "excluding BIER incapable routers", i.e., BIER incapable routers are 166 not put onto the candidate list during SPF calculation. 168 Note that if the BC and RC happen to conflict and lead to an empty 169 topology, then no native BIER forwarding path will be found. That is 170 a network design issue that an operator need to avoid when choosing 171 BAR/IPA. 173 4. IANA Considerations 175 No IANA Consideration is requested in this document. 177 5. Security Considerations 179 This document does not change the security aspects as discussed in 180 [RFC8279]. 182 6. Acknowledgements 184 The authors thank Alia Atlas, Eric Rosen, Senthil Dhanaraj and many 185 others for their suggestions and comments. In particular, the BCBA/ 186 RCRA representation for the interaction rules is based on Alia's 187 write-up. 189 7. References 191 7.1. Normative References 193 [I-D.ietf-bier-ospfv3-extensions] 194 Psenak, P., Nainar, N. K., and I. Wijnands, "OSPFv3 195 Extensions for BIER", draft-ietf-bier-ospfv3-extensions-04 196 (work in progress), May 2021. 198 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 199 Requirement Levels", BCP 14, RFC 2119, 200 DOI 10.17487/RFC2119, March 1997, 201 . 203 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 204 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 205 May 2017, . 207 [RFC8401] Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z. 208 Zhang, "Bit Index Explicit Replication (BIER) Support via 209 IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018, 210 . 212 [RFC8444] Psenak, P., Ed., Kumar, N., Wijnands, IJ., Dolganow, A., 213 Przygienda, T., Zhang, J., and S. Aldrin, "OSPFv2 214 Extensions for Bit Index Explicit Replication (BIER)", 215 RFC 8444, DOI 10.17487/RFC8444, November 2018, 216 . 218 7.2. Informative References 220 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 221 Topology (MT) Routing in Intermediate System to 222 Intermediate Systems (IS-ISs)", RFC 5120, 223 DOI 10.17487/RFC5120, February 2008, 224 . 226 [RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A., 227 Przygienda, T., and S. Aldrin, "Multicast Using Bit Index 228 Explicit Replication (BIER)", RFC 8279, 229 DOI 10.17487/RFC8279, November 2017, 230 . 232 Authors' Addresses 233 Zhaohui Zhang 234 Juniper Networks 236 EMail: zzhang@juniper.net 238 Antoni Przygienda 239 Juniper Networks 241 EMail: prz@juniper.net 243 Andrew Dolganow 244 Individual 246 EMail: adolgano@gmail.com 248 Hooman Bidgoli 249 Nokia 251 EMail: hooman.bidgoli@nokia.com 253 IJsbrand Wijnands 254 Individual 256 EMail: ice@braindump.be 258 Arkadiy Gulko 259 Edward Jones Wealth Management 261 EMail: arkadiy.gulko@edwardjones.com