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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (12 May 2022) is 712 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BIER Z. Zhang 3 Internet-Draft A. Przygienda 4 Updates: 8401, 8444 (if approved) Juniper Networks 5 Intended status: Standards Track A. Dolganow 6 Expires: 13 November 2022 Individual 7 H. Bidgoli 8 Nokia 9 I. Wijnands 10 Individual 11 A. Gulko 12 Edward Jones Wealth Management 13 12 May 2022 15 BIER Underlay Path Calculation Algorithm and Constraints 16 draft-ietf-bier-bar-ipa-13 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 and RFC8444. This document also updates the BIER Algorithm 24 registry established in RFC8401. 26 Requirements Language 28 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 29 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 30 "OPTIONAL" in this document are to be interpreted as described in BCP 31 14 [RFC2119] [RFC8174] when, and only when, they appear in all 32 capitals, as shown here. 34 Status of This Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at https://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on 13 November 2022. 50 Copyright Notice 52 Copyright (c) 2022 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 (https://trustee.ietf.org/ 57 license-info) in effect on the date of publication of this document. 58 Please review these documents carefully, as they describe your rights 59 and restrictions with respect to this document. Code Components 60 extracted from this document must include Revised BSD License text as 61 described in Section 4.e of the Trust Legal Provisions and are 62 provided without warranty as described in the Revised BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 67 2. Updated Definition for BAR and IPA Fields . . . . . . . . . . 3 68 3. General Rules for the BAR and IPA Interaction . . . . . . . . 3 69 3.1. When BAR Is Not Used . . . . . . . . . . . . . . . . . . 4 70 3.2. Exceptions/Extensions to the General Rules . . . . . . . 4 71 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4 72 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 73 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 74 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 75 8. Normative References . . . . . . . . . . . . . . . . . . . . 5 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 78 1. Introduction 80 In the Bit Index Explicit Replication (BIER) architecture [RFC8279], 81 packets with a BIER encapsulation header are forwarded to the 82 neighbors on the underlay paths towards Bit-Forwarding Egress Routers 83 (BFERs) that are represented by bits set in the BIER header's 84 BitString. The paths are calculated in the underlay topology for 85 each sub-domain following a calculation algorithm specific to the 86 sub-domain. The topology or algorithm may or may not be congruent 87 with unicast. The algorithm could be a BIER specific algorithm or 88 could be a generic IGP one, e.g., Shortest Path First (SPF). 90 In [RFC8401] and [RFC8444], an 8-bit BAR (BIER Algorithm) field and 91 8-bit IPA (IGP Algorithm) field are defined to signal the BIER 92 specific algorithm and generic IGP Algorithm respectively and only 93 value 0 is allowed for both fields in those two documents. 95 This document specifies general rules for the interaction between the 96 BIER Algorithm (BAR) and the IGP Algorithm (IPA) used for underlay 97 path calculation when other BAR and/or IPA values are used. The 98 semantics defined in this document update [RFC8401], [RFC8444]. This 99 document also updates the BIER Algorithm registry defined in 100 [RFC8401] by renaming the "Experimental Use" range to "Private or 101 Experimental Use". 103 2. Updated Definition for BAR and IPA Fields 105 The definition for the BAR and IPA fields in Section 6.1 of [RFC8401] 106 and Section 2.1 of [RFC8444] are updated as follows. 108 IPA: IGP Algorithm. Specifies a generic Routing Algorithm (RA) and 109 related Routing Constraints (RC) to calculate underlay paths to reach 110 other Bit-Forwarding Routers (BFRs). Values are from the "IGP 111 Algorithm Types" registry. One Octet. 113 BAR: BIER Algorithm. Specifies a BIER-specific Algorithm (BA) and 114 BIER-specific Constraints (BC) used to either modify, enhance, or 115 replace the calculation of underlay paths to reach other BFRs as 116 defined by the IPA value. Values are allocated from the "BIER 117 Algorithm" registry. One Octet. 119 When a BAR value is defined, the corresponding BA and BC semantics 120 SHOULD be specified. For an IGP Algorithm to be used as a BIER IPA, 121 its RA and RC semantics SHOULD be specified. If any of these 122 semantics is not specified, it MUST be interpreted as "NULL" 123 algorithm or constraint. For example, the IGP Algorithm 0 defined in 124 [RFC8665] is treated as having a NULL RC, i.e., no constraints (see 125 Section 3). 127 If a specification is not available for a specific BAR value, its 128 value MUST be from the Private or Experimental Use range of the 129 registry. 131 3. General Rules for the BAR and IPA Interaction 133 For a particular sub-domain, all BFRs MUST be provisioned with and 134 signal the same BAR and IPA values. If a BFR discovers another BFR 135 advertising different BAR or IPA value for a sub-domain, it MUST 136 treat the advertising router as incapable of supporting BIER for that 137 sub-domain (one way of handling incapable routers is documented in 138 Section 6.9 of [RFC8279] and additional methods may be defined in the 139 future). 141 For a particular topology X that a sub-domain is associated with, a 142 router MUST calculate the underlay paths according to its BAR and IPA 143 values in the following way: 145 1. Apply the BIER constraints, resulting in BC(X). If BC is NULL, 146 then BC(X) is X itself. 148 2. Apply the routing constraints, resulting in RC(BC(X)). If RC is 149 NULL, then RC(BC(X)) is BC(X). 151 3. Select the algorithm AG as following: 153 a. If BA is NULL, AG is set to RA. 155 b. If BA is not NULL, AG is set to BA. 157 4. Run AG on RC(BC(X)). 159 It's possible that the resulting AG is not applicable to BIER, In 160 that case, no BIER paths will be calculated and it is a network 161 design issue that an operator needs to avoid when choosing BAR/IPA. 163 3.1. When BAR Is Not Used 165 BAR value 0 is defined as "No BIER-specific algorithm is used" 166 [RFC8401]. This value indicates NULL BA and BC. Following the rules 167 defined above, the IPA value alone identifies the calculation 168 algorithm and constraints to be used for a particular sub-domain. 170 3.2. Exceptions/Extensions to the General Rules 172 Exceptions or extensions to the above general rules may be specified 173 in the future for specific BAR and/or IPA values. When that happens, 174 compatibility with defined BAR and/or IPA values and semantics need 175 to be specified. 177 4. Examples 179 As an example, one may define a new BAR with a BIER specific 180 constraint of "excluding BIER incapable routers". No BIER specific 181 algorithm is specified, and the BIER specific constraint can go with 182 any IPA - whatever RC defined by the IPA is augmented with "excluding 183 BIER incapable routers", i.e., routers that do not support BIER are 184 not considered when applying the IGP Algorithm. 186 If the BC and RC happen to conflict and lead to an empty topology, 187 then no BIER forwarding path will be found. For example, the BC 188 could be "exclude BIER-incapable routers" and the RC could be 189 "include green links only". If all the green links are associated 190 with BIER-incapable routers, it results in an empty topology. That 191 is a network design issue that an operator needs to avoid when 192 choosing BAR/IPA. 194 In another example, a BAR value can be specified to use Steiner Tree 195 algorithm and used together with IPA 0 (which uses SPF algorithm). 196 According to the general rules, the BIER specific algorithm takes 197 precedence so SPF is not used. 199 5. IANA Considerations 201 This document requests the following changes to the "BIER Algorithm" 202 registry: 204 1. Rename the "Experimental Use" range to "Private or Experimental 205 Use" 207 2. Add this document as a reference 209 6. Security Considerations 211 This document specifies general rules for the interaction between the 212 BIER Algorithm (BAR) and the IGP Algorithm (IPA) used for underlay 213 path calculation. It does not change the security aspects as 214 discussed in [RFC8279], [RFC8401], [RFC8444]. 216 7. Acknowledgements 218 The authors thank Alia Atlas, Eric Rosen, Senthil Dhanaraj and many 219 others for their suggestions and comments. In particular, the 220 BC/BA/RC/RA representation for the interaction rules is based on 221 Alia's write-up. 223 8. Normative References 225 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 226 Requirement Levels", BCP 14, RFC 2119, 227 DOI 10.17487/RFC2119, March 1997, 228 . 230 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 231 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 232 May 2017, . 234 [RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A., 235 Przygienda, T., and S. Aldrin, "Multicast Using Bit Index 236 Explicit Replication (BIER)", RFC 8279, 237 DOI 10.17487/RFC8279, November 2017, 238 . 240 [RFC8401] Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z. 241 Zhang, "Bit Index Explicit Replication (BIER) Support via 242 IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018, 243 . 245 [RFC8444] Psenak, P., Ed., Kumar, N., Wijnands, IJ., Dolganow, A., 246 Przygienda, T., Zhang, J., and S. Aldrin, "OSPFv2 247 Extensions for Bit Index Explicit Replication (BIER)", 248 RFC 8444, DOI 10.17487/RFC8444, November 2018, 249 . 251 [RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, 252 H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 253 Extensions for Segment Routing", RFC 8665, 254 DOI 10.17487/RFC8665, December 2019, 255 . 257 Authors' Addresses 259 Zhaohui Zhang 260 Juniper Networks 261 Email: zzhang@juniper.net 263 Antoni Przygienda 264 Juniper Networks 265 Email: prz@juniper.net 267 Andrew Dolganow 268 Individual 269 Email: adolgano@gmail.com 271 Hooman Bidgoli 272 Nokia 273 Email: hooman.bidgoli@nokia.com 275 IJsbrand Wijnands 276 Individual 277 Email: ice@braindump.be 278 Arkadiy Gulko 279 Edward Jones Wealth Management 280 Email: arkadiy.gulko@edwardjones.com