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Bidgoli, Ed. 3 Internet-Draft Nokia 4 Intended status: Informational F. Xu 5 Expires: January 30, 2021 Verizon 6 J. Kotalwar 7 Nokia 8 I. Wijnands 9 M. Mishra 10 Cisco System 11 Z. Zhang 12 Juniper Networks 13 July 29, 2020 15 PIM Signaling Through BIER Core 16 draft-ietf-bier-pim-signaling-10 18 Abstract 20 Consider large networks deploying traditional PIM multicast service. 21 Typically, each portion of these large networks have their own 22 mandates and requirements. 24 It might be desirable to deploy BIER technology in some part of these 25 networks to replace traditional PIM services. In such cases 26 downstream PIM states need to be signaled over BIER Domain toward the 27 source. 29 This draft explains the procedure to signal PIM joins and prunes 30 through a BIER Domain, as such enable provisioning of traditional PIM 31 services through a BIER Domain. 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 January 30, 2021. 50 Copyright Notice 52 Copyright (c) 2020 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. Conventions used in this document . . . . . . . . . . . . . . 3 69 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3 70 3. PIM Signaling Through BIER domain . . . . . . . . . . . . . . 5 71 3.1. Ingress BBR procedure . . . . . . . . . . . . . . . . . . 5 72 3.1.1. Determining EBBR on IBBR . . . . . . . . . . . . . . 6 73 3.1.2. Considering ECMP in EBBR selection . . . . . . . . . 6 74 3.1.3. PIM Signaling packet construction at IBBR . . . . . . 7 75 3.1.3.1. BIER packet construction at IBBR . . . . . . . . 8 76 3.2. Signaling PIM through the BIER domain procedure . . . . . 8 77 3.3. EBBR procedure . . . . . . . . . . . . . . . . . . . . . 9 78 4. Datapath Forwarding . . . . . . . . . . . . . . . . . . . . . 9 79 4.1. BFIR tracking of (S,G) . . . . . . . . . . . . . . . . . 9 80 4.2. Datapath traffic flow . . . . . . . . . . . . . . . . . . 9 81 5. PIM-SM behavior . . . . . . . . . . . . . . . . . . . . . . . 9 82 6. Applicability to MVPN . . . . . . . . . . . . . . . . . . . . 10 83 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 84 8. Security Considerations . . . . . . . . . . . . . . . . . . . 11 85 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 86 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 87 10.1. Normative References . . . . . . . . . . . . . . . . . . 11 88 10.2. Informative References . . . . . . . . . . . . . . . . . 11 89 Appendix A. . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 90 A.1. SPF . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 91 A.2. Indirect next-hop . . . . . . . . . . . . . . . . . . . . 12 92 A.2.1. Static Route . . . . . . . . . . . . . . . . . . . . 12 93 A.2.2. Interior Border Gateway Protocol (iBGP) . . . . . . . 13 94 A.3. Inter-area support . . . . . . . . . . . . . . . . . . . 13 95 A.3.1. Inter-area Route summarization . . . . . . . . . . . 13 96 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 98 1. Introduction 100 Consider large networks deploying traditional PIM multicast service. 101 Typically, each portion of these large networks have their own 102 mandates and requirements. 104 It might be desirable to deploy BIER technology in some part of these 105 networks to replace traditional PIM services. In such cases 106 downstream PIM states need to be signaled over BIER Domain toward the 107 source. 109 This draft explains the procedure to signal PIM joins and prunes 110 through a BIER Domain, as such enable provisioning of traditional PIM 111 services through a BIER Domain. 113 2. Conventions used in this document 115 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 116 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 117 document are to be interpreted as described in RFC 2119 [RFC2119]. 119 2.1. Definitions 121 Some of the terminology specified in [RFC8279] is replicated here and 122 extended by necessary definitions: 124 BIER: 126 Bit Index Explicit Replication (The overall architecture of 127 forwarding multicast using a Bit Position). 129 BFR: 131 Bit Forwarding Router (A router that participates in Bit Index 132 Multipoint Forwarding).A BFR is identified by a unique BFR-prefix in 133 a BIER domain. 135 BFIR: 137 Bit Forwarding Ingress Router (The ingress border router that 138 performs BIER encapsulation). Each BFIR must have a valid BFR-id 139 assigned. In this draft BIER will be used for forwarding and 140 tunneling of control plane packet (i.e. PIM) and forwarding 141 dataplane packets. BFIR is term used for dataplane packet 142 forwarding. 144 BFER: 146 Bit Forwarding Egress Router. A router that participates in Bit 147 Index Forwarding as leaf. Each BFER must have a valid BFR-id 148 assigned. In this draft BIER will be used for forwarding and 149 tunneling of control plane packet (i.e. PIM) and forwarding 150 dataplane packets. BFIR is term used for dataplane packet 151 forwarding. 153 BBR: 155 BIER Boundary router. A router between the PIM domain and BIER 156 domain. Maintains PIM adjacency for all routers attached to it on 157 the PIM domain and terminates the PIM adjacency toward the BIER 158 domain. 160 IBBR: 162 Ingress BIER Boundary Router. An ingress router from signaling point 163 of view. It maintains PIM adjacency toward the PIM domain and 164 determines if PIM joins and prunes arriving from PIM domain need to 165 be signaled across the BIER domain. If so it terminates the PIM 166 adjacency toward the BIER domain and signals the PIM joins/prunes 167 through the BIER core. 169 EBBR: 171 Egress BIER Boundary Router. An egress router in BIER domain from 172 signaling point of view. It terminates the BIER packet and forwards 173 the signaled joins and prunes into PIM Domain. 175 BFT: 177 Bit Forwarding Tree used to reach all BFERs in a domain. 179 BIFT: 181 Bit Index Forwarding Table. 183 BIER sub-domain: 185 A further distinction within a BIER domain identified by its unique 186 sub-domain identifier. A BIER sub-domain can support multiple 187 BitString Lengths. 189 BFR-id: 191 An optional, unique identifier for a BFR within a BIER sub-domain. 193 3. PIM Signaling Through BIER domain 195 BBR BBR 196 |--PIM Domain--|-----BIER domain-----|--PIM domain--| 197 S--( A )----------( B ) ---- ( C ) ---- ( D )----------( E )--h 199 EBBR IBBR 200 Sig <-----PIM-----|<--BIER Tunneling----|<----PIM------ 201 (new) 202 BFIR BFER 203 ------------->|--------BIER-------->|-------------> Datapath 204 (no change) 206 Figure 1: BIER boundry router 208 As per figure 1, the procedures of PIM signaling is done at the BIER 209 boundary router. The BIER boundary routers (BBR) are connected to 210 PIM capable routers toward the PIM domain and BIER routers toward the 211 BIER domain. PIM routers in PIM domain continue to send PIM state 212 messages to the BBR. The BBR will create PIM adjacency between all 213 the PIM routers attached to it on the PIM domain. That said the BBR 214 does not propagate all PIM packets natively into the BIER domain. 215 Instead when it determines that the PIM join or prune messages needs 216 to be signaled through the BIER domain it will tunnel the PIM packet 217 through the BIER network. This tunneling is only done for signaling 218 purposes and not for creating a PIM adjacency between the two 219 disjoint PIM domains through the BIER domain. 221 The terminology ingress BBR (IBBR) and egress BBR (EBBR) are relative 222 from signaling point of view. 224 The ingress BBR will determine if an arriving PIM join or prune needs 225 to be signaled across the BIER domain. While the egress BBR will 226 determine if the arriving BIER packet is a signaling packet and if so 227 it will generate a PIM join/prune packet toward its attached PIM 228 domain. 230 The BFER and BFIR are BBR from datapath point of view. It should be 231 noted the new procedures in this draft are only applicable to 232 signaling and there are no changes from datapath point of view. 234 3.1. Ingress BBR procedure 236 IBBR will create PIM adjacency to all PIM routers attached to it 237 toward the PIM domain. 239 When a PIM join or prune for certain (S,G) arrives, the IBBR first 240 determines whether the join or prune is meant for a source that is 241 reachable through the BIER domain. As an example, this source is 242 located in a disjoint PIM domain that is reachable through the BIER 243 domain. If so the IBBR will try to resolve the source via an EBBR 244 closest to the source. 246 The procedure to find the EBBR (BFIR from datapath point of view) can 247 be via many mechanisms explained in more detail in upcoming section. 249 After discovering the EBBR and its BFR-ID, the IBBR will include a 250 new PIM Join Attribute in the join/prune message as per [RFC5384]. 251 Two new "BIER IBBR" attributes are defined and explained in upcoming 252 section. The PIM Join Attribute is used on EBBR to obtain necessary 253 BIER information to build its multicast states. In addition the IBBR 254 will change the PIM signaling packet source IP address to its BIER 255 prefix address (standard PIM procedure). It will also keep the 256 destination address as the well known multicast IP address. It then 257 will construct the BIER header. The signaling packet, in this case 258 the PIM join/prune packet, is encapsulated in the BIER header and 259 transported through BIER domain to EBBR. 261 The IBBR will track all the PIM interfaces on the attached PIM domain 262 which are interested in a certain (S,G). It creates multicast states 263 for arriving (S,G)s from PIM domain, with incoming interface as BIER 264 "tunnel" interface and outgoing interface as the PIM domain 265 interface(s) on which PIM Join(s) were received on. 267 3.1.1. Determining EBBR on IBBR 269 As it was explained in previous section, IBBR needs to determine the 270 EBBR closest to the source. This is needed to encode the BIER header 271 BitString field to forward the signaling packet through the BIER 272 domain. 274 It should be noted, the PIM domains can be either part of the same 275 IGP area as BIER domain(single area) or are stitched to the BIER 276 domain via an ABR or ASBR routers. As such on IBBR, there can be 277 many different procedures to determine the EBBR. Some examples of 278 these procedures have been provided in Appendix A. 280 3.1.2. Considering ECMP in EBBR selection 282 If the lookup for source results into multiple EBBRs, then the EBBR 283 selection algorithm should ensure that all signaling for a particular 284 (C-S, C-G) is forward to a single EBBR. How the this selection is 285 done is vendor specific and beyond this draft. As an example it can 286 be round robin per (C-S, C-G) or smallest EBBR IP for all (C-S, 287 C-G)s. 289 3.1.3. PIM Signaling packet construction at IBBR 291 To ensure all necessary BIER information needed by EBBR is present in 292 the BIER signaling message, a new PIM Join Attribute [RFC5384] is 293 used. EBBR can use this attribute to build its multicast states, as 294 described in EBBR procedure section. This new PIM join Attribute is 295 added to PIM signaling message on the IBBR. Its format is as follow: 297 0 1 2 3 298 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 300 |F|E| Type=tbd | Length | Addr Family | BIER info 301 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-... 303 Figure 2: PIM Join Attribute 305 F bit: The Transitive bit. Specifies whether this attribute is 306 transitive or non-transitive. MUST be set to zero. This attribute 307 is ALWAYS non-transitive. 309 E bit: End-of-Attributes bit. Specifies whether this attribute is 310 the last. Set to zero if there are more attributes. Set to 1 if 311 this is the last attribute. 313 Type: TBD assign by IANA 315 Length: The length in octets of the attribute value. MUST be set to 316 the length in octets of the BIER info +1 octet to account for the 317 Address Family field. For IPv4 AF Length = 7+1 For IPv6 AF Length = 318 19+1 320 Addr Family: Signaled PIM Join/Prune address family as defined in 321 [RFC7761] 323 BIER Info: IBBR Prefix (IPv4 or IPv6), SD, bfr-id as per below figure 325 0 1 2 3 326 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 327 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 328 ~ IBBR Prefix IPv4 or IPv6 ~ 329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 330 | subdomain-id | BFR-ID | 331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 Figure 3: PIM Join Attribute detail 335 3.1.3.1. BIER packet construction at IBBR 337 The BIER header will be encoded with the BFR-id of the IBBR(with 338 appropriate bit set in the bitstring) and the PIM signaling packet is 339 then encapsulated in the packet. 341 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 343 | BIFT-id | TC |S| TTL | 344 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 345 |Nibble | Ver | BSL | Entropy | 346 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 347 |OAM|Rsv| DSCP | Proto | BFIR-id | 348 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 349 | BitString (first 32 bits) ~ 350 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 351 ~ ~ 352 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 353 ~ BitString (last 32 bits) | 354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 356 Figure 4: BIER header 358 BIERHeader.Proto = IPv4 or IPv6 360 BIERHeader.BitString= Bit corresponding to the BFR-ID of the EBBR 362 BIERHeader.BFIR-id = BFR-Id of the BER originating the encapsulated 363 PIM packet, i.e. the IBBR. 365 Rest of the values in the BIER header are determined based on the 366 network (MPLS/non-MPLS), capabilities (BSL), and network 367 configuration. 369 3.2. Signaling PIM through the BIER domain procedure 371 Throughout the BIER domain the BIER forwarding procedure is on par 372 with [RFC8279]. No BIER router will examine the BIER packet 373 encapsulating the PIM signaling packet. As such there is no 374 multicast state built in the BIER domain. 376 The packet will be forwarded through the BIER domain until it reaches 377 the BER with matching BFR-ID as in the BIERHeader.Bitstring. EBBR 378 will remove the BIER header and examine the PIM IPv4 or IPv6 379 signaling packet farther as per EBBR Procedure section. 381 3.3. EBBR procedure 383 EBBR will remove the BIER header and determine this is a signaling 384 packet. The Received PIM join/prune Signaling packet is processed as 385 if it were received from neighbors on a virtual interface, (i.e. as 386 if the pim adjacency was presents, regardless of the fact there is no 387 adjacency) 389 The EBBR will build a forwarding table for the arriving (S,G) using 390 the obtained BFIR-id and the Sub-Domain information from BIER Header 391 and/or the PIM join Attributes added to the PIM Signaling packet. In 392 short it tracks all IBBRs interested in this (S,G). This is 393 explained in section 4.1. 395 The multicast state on EBBR will contain PIM domain incoming 396 interfaces, according to PIM specification and outgoing interfaces 397 based on the above build forwarding table. 399 It should be noted EBBR will maintain PIM adjacency toward the PIM 400 domain and all PIM routers which are connected to it. At this point 401 the end-to-end multicast traffic flow setup is complete. 403 4. Datapath Forwarding 405 4.1. BFIR tracking of (S,G) 407 For a specific Source and Group, BFIR (EBBR)should track all the 408 interested BFERs (IBBRs) via arriving PIM signaling from BIER Domain. 409 BFIR builds its (s,g)forwarding state with incoming interface (IIF) 410 as the RPF interface (in PIM domain) towards the source and one of 411 the outgoing interfaces as for sending to tracked BFERs in the SD. 413 4.2. Datapath traffic flow 415 When the multicast data traffic arrives on the BFIR (EBBR) the router 416 will find all the interested BFERs for that specific (S,G). The 417 router then constructs the BIERHeader.BitString with all the BFER 418 interested in the group and will forward the packet to the BIER 419 domain. The BFER(s) will accept the packets and remove the BIER 420 header and forward the multicast packet as per pre-build multicast 421 state for (S,G) and its outgoing interfaces. 423 5. PIM-SM behavior 425 The procedures described in this document can work with ASM as long 426 as static RP or embedded RP for IPv6 is used. Future drafts would 427 cover BSR and more complicated SM discovery mechanisms. 429 It should be noted that this draft only signals PIM Joins and Prunes 430 through the BIER domain and not any other PIM message types including 431 PIM Hellos or Asserts. As such functionality related to these other 432 type of massages will not be possible through a BIER domain with this 433 draft and future drafts might cover these scenarios. As an example 434 DR selection should be done in the PIM domain or if the PIM routers 435 attached to IBBRs are performing DR selection there needs to be a 436 dedicated PIM interface between these routers. 438 In case of PIM ASM Static RP or embedded RP for IPv6 the procedure 439 for leaves joining RP is same as above. It should be noted that for 440 ASM, the EBBRs are determined with respect to the RP instead of the 441 source. 443 6. Applicability to MVPN 445 With just minor changes, the above procedures apply to MVPN as well, 446 with BFIR/BFER/EBBR/IBBR being VPN PEs. All the PIM related 447 procedures, and the determination of EBBR happens in the context of a 448 VRF, following procedures for PIM-MVPN. 450 When a PIM packet arrives from PIM domain attached to the VRF (IBBR), 451 and it is determined that the source is reachable via the VRF through 452 the BIER domain, a PIM signaling message is sent via BIER to the 453 EBBR. In this case usually the PE terminating the PIM-MVPN is the 454 EBBR. A label is imposed before the BIER header is imposed, and the 455 "proto" field in the BIER header is set to 1 (for "MPLS packet with 456 downstream-assigned label at top of stack"). The label is advertised 457 by the EBBR/BFIR to associate incoming packets to its correct VRF. 458 In many scenarios a label is already bound to the VRF loopback 459 address on the EBBR/BFIR and it can be used. 461 When a multicast data packet is sent via BIER by an EBBR/BFIR, a 462 label is imposed before the BIER packet is imposed, and the "proto" 463 field in the BIER header is set to 1 (for "MPLS packet with 464 downstream-assigned label at top of stack"). The label is assigned 465 to the VPN consistently on all VRFs 466 [draft-zzhang-bess-mvpn-evpn-aggregation-label-01]. 468 If the more complicated label allocation scheme is needed for the 469 data packets as specified in 470 [draft-zzhang-bess-mvpn-evpn-aggregation-label-01], then additional 471 PMSI signaling is needed as specified in [RFC6513]. 473 To support per-area subdomain in this case, the ABRs would need to 474 become VPN PEs and maintain per-VPN state so it is unlikely 475 practical. 477 7. IANA Considerations 479 In the "PIM Join Attribute Types" registry, IANA to assigned a new 480 value [TBD] to the BIER Info Vector. 482 8. Security Considerations 484 The procedures of this document do not, in themselves, provide 485 privacy, integrity, or authentication for the control plane or the 486 data plane. For a discussion of the security considerations 487 regarding the use of BIER, please see [RFC8279] and [RFC8296]. 488 Security considerations regarding PIM protocol is based on [RFC7761]. 490 9. Acknowledgments 492 The authors would like to thank Eric Rosen, Stig Venaas for thier 493 reviews and comments. 495 10. References 497 10.1. Normative References 499 [RFC4607] "H. Holbrook, B. Cain, "Source-Specific multicast for 500 IP"", October 2016. 502 [RFC8279] "Wijnands, IJ., Rosen, E., Dolganow, A., Przygienda, T. 503 and S. Aldrin, "Multicast using Bit Index Explicit 504 Replication"", October 2016. 506 10.2. Informative References 508 [draft-zzhang-bess-mvpn-evpn-aggregation-label-01] 509 "Z. Zhang, E. Rosen, W. Lin, Z. Li, I.Wijnands, "MVPN/EVPN 510 Tunnel Aggregation with Common labels"", April 2018. 512 [RFC5384] "A. Boers, I. Wijnands, E. Rosen, "PIM Join Attribute 513 Format"", November 2008. 515 [RFC6513] "E. Rosen, R. Aggarwal, "Multicast in MPLS/BGP IP VPNs"", 516 November 2008. 518 [RFC6826] "IJ. Wijnands, T. Echert, N. Leymann, M. Napierala, 519 "Multipoint LDP In-Band Singnaling for PtP MPtMP LSP"", 520 January 2013. 522 [RFC7761] "B.Fenner, M.Handley, H. Holbrook, I. Kouvelas, R. Parekh, 523 Z.Zhang "PIM Sparse Mode"", March 2016. 525 [RFC8296] "IJ. Wijnands, E. Rosen, A. Dolganow, J. Yantsura, S. 526 Aldrin, I. Meilik, "Encapsulation for BIER"", January 527 2018. 529 [RFC8401] "Ginsberg, L., Przygienda, T., Aldrin, S., and Z. Zhang, 530 "BIER Support via ISIS"", June 2018. 532 [RFC8444] "Psenak, P., Kumar, N., Wijnands, IJ., Dolganow, A., 533 Przygienda, T., Zhang, Z., and S. Aldrin, "OSPF Extensions 534 for Bit Index Explicit Replication"", June 2018. 536 [RFC8556] "Rosen, E., Ed., Sivakumar, M., Wijnands, IJ., Aldrin, 537 S.,Dolganow, A., and T. Przygienda, "Multicast VPN Using 538 BIER"", March 2018. 540 Appendix A. 542 This appendix provides some examples and routing procedures that can 543 be used to determine the EBBR on IBBR. It should be noted, the PIM 544 domains can be either part of the same IGP area as BIER domain(single 545 area) or are stitched to the BIER domain via an ABR or ASBR routers. 546 As such on IBBR, there can be many different procedures to determine 547 the EBBR. Not all procedures are listed below. 549 A.1. SPF 551 On IBBR SPF procedures can be used to find the EBBR closest to the 552 source. 554 Assuming the BIER domain consists of all BIER forwarding routers, SPF 555 calculation can identify the router advertising the prefix for the 556 source. A post process can find the EBBR by walking from the 557 advertising router back to the IBBR in the reverse direction of 558 shortest path tree branch until the first BFR is encountered. 560 A.2. Indirect next-hop 562 Alternatively, the route to the source could have an indirect next- 563 hop that identifies the EBBR. These methods are explained in the 564 following sections. 566 A.2.1. Static Route 568 On IBBR there can be a static route configured for the source, with 569 source next-hop set as EBBR BIER prefix. 571 A.2.2. Interior Border Gateway Protocol (iBGP) 573 Consider the following topology: 575 BBR BBR 576 EBBR IBBR 577 |--PIM Domain--|-----BIER domain-----|--PIM domain--| 578 S--( A )----------( B ) ---- ( C ) ---- ( D )----------( E )--h 580 Figure 2 582 Figure 5: Static Route 584 Suppose BGP is enable between EBBR (B) and IBBR (D) and the PIM 585 Domain routes are redistributed to the BIER domain via BGP. This 586 would include the Multicast Source IP address (S), which resides in 587 the PIM Domain. In such case BGP should use the same loopback 588 interface as its next-hop as the BBR prefix. This will ensure that 589 all PIM domain routes, including the Multicast Source IP address (S) 590 are resolve via BBR's BIER prefix id as their next-hop. When the 591 host (h) triggers a PIM join message to IBBR (D), IBBR tries to 592 resolve (S). It resolves (S) via BGP installed route and realizes 593 its next-hop is EBBR (B). IBBR will use this next-hop (B) to find 594 its corresponding BIER bit index. 596 This procedure is inline with [RFC6826] mLDP in-band signaling 597 section 599 A.3. Inter-area support 601 If each area has its own BIER sub-domain, the above procedure for 602 post-SPF could identify one of the ABRs and the EBBR. If a sub- 603 domain spans multiple areas, then additional procedures as described 604 in A.2 is needed. 606 A.3.1. Inter-area Route summarization 608 In a multi-area topology, a BIER sub-domain can span a single area. 609 Suppose this single area is constructed entirely of BIER capable 610 routers and the ABRs are the BIER Boundary Routers attaching the BIER 611 sub-domain in this area to PIM domains in adjacent areas. These BBRs 612 can summarize the PIM domain routes via summary routes, as an example 613 for OSPF, a type 3 summary LSAs can be used to advertise summary 614 routes from a PIM domain area to the BIER area. In such scenarios 615 the IBBR can be configured to look up the Source via IGP database and 616 use the summary routes and its Advertising Router field to resolve 617 the EBBR. The IBBR needs to ensure that the IGP summary route is 618 generated by a BFR. This can be achieved by ensuring that BIER Sub- 619 TLV exists for this route. If multiple BBRs (ABRs) have generated 620 the same summary route the lowest Advertising Router IP can be 621 selected or a vendor specific hashing algorithm can select the 622 summary route from one of the BBRs. 624 Authors' Addresses 626 Hooman Bidgoli (editor) 627 Nokia 628 Ottawa 629 Canada 631 Email: hooman.bidgoli@nokia.com 633 Fengman Xu 634 Verizon 635 Richardson 636 US 638 Email: fengman.xu@verizon.com 640 Jayant Kotalwar 641 Nokia 642 Montain View 643 US 645 Email: jayant.kotalwar@nokia.com 647 IJsbrand Wijnands 648 Cisco System 649 Diegem 650 Belgium 652 Email: ice@cisco.com 654 Mankamana Mishra 655 Cisco System 656 Milpitas 657 USA 659 Email: mankamis@cisco.com 660 Zhaohui Zhang 661 Juniper Networks 662 Boston 663 USA 665 Email: zzhang@juniper.com