idnits 2.17.1 draft-ietf-bess-mvpn-global-table-mcast-01.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (May 18, 2015) is 3260 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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-15) exists of draft-ietf-idr-add-paths-10 == Outdated reference: A later version (-07) exists of draft-ietf-bess-mvpn-extranet-02 -- Obsolete informational reference (is this intentional?): RFC 4601 (Obsoleted by RFC 7761) Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BESS Working Group Z. Zhang 3 Internet-Draft L. Giuliano 4 Intended status: Standards Track E. Rosen, Ed. 5 Expires: November 19, 2015 Juniper Networks, Inc. 6 K. Subramanian 7 Cisco Systems, Inc. 8 D. Pacella 9 Verizon 10 J. Schiller 11 Google 12 May 18, 2015 14 Global Table Multicast with BGP-MVPN Procedures 15 draft-ietf-bess-mvpn-global-table-mcast-01 17 Abstract 19 RFC6513, RFC6514, and other RFCs describe protocols and procedures 20 which a Service Provider (SP) may deploy in order offer Multicast 21 Virtual Private Network (Multicast VPN or MVPN) service to its 22 customers. Some of these procedures use BGP to distribute VPN- 23 specific multicast routing information across a backbone network. 24 With a small number of relatively minor modifications, the very same 25 BGP procedures can also be used to distribute multicast routing 26 information that is not specific to any VPN. Multicast that is 27 outside the context of a VPN is known as "Global Table Multicast", or 28 sometimes simply as "Internet multicast". In this document, we 29 describe the modifications that are needed to use the MVPN BGP 30 procedures for Global Table Multicast. 32 Status of This Memo 34 This Internet-Draft is submitted in full conformance with the 35 provisions of BCP 78 and BCP 79. 37 Internet-Drafts are working documents of the Internet Engineering 38 Task Force (IETF). Note that other groups may also distribute 39 working documents as Internet-Drafts. The list of current Internet- 40 Drafts is at http://datatracker.ietf.org/drafts/current/. 42 Internet-Drafts are draft documents valid for a maximum of six months 43 and may be updated, replaced, or obsoleted by other documents at any 44 time. It is inappropriate to use Internet-Drafts as reference 45 material or to cite them other than as "work in progress." 47 This Internet-Draft will expire on November 19, 2015. 49 Copyright Notice 51 Copyright (c) 2015 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (http://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the Simplified BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 67 2. Adapting MVPN Procedures to GTM . . . . . . . . . . . . . . . 5 68 2.1. Use of Route Distinguishers . . . . . . . . . . . . . . . 5 69 2.2. Use of Route Targets . . . . . . . . . . . . . . . . . . 6 70 2.3. UMH-eligible Routes . . . . . . . . . . . . . . . . . . . 8 71 2.3.1. Routes of SAFI 1, 2 or 4 with MVPN ECs . . . . . . . 9 72 2.3.2. MVPN ECs on the Route to the Next Hop . . . . . . . . 10 73 2.3.3. Non-BGP Routes as the UMH-eligible Routes . . . . . . 11 74 2.3.4. Why SFS Does Not Apply to GTM . . . . . . . . . . . . 11 75 2.4. Inclusive and Selective Tunnels . . . . . . . . . . . . . 13 76 2.5. I-PMSI A-D Routes . . . . . . . . . . . . . . . . . . . . 13 77 2.5.1. Intra-AS I-PMSI A-D Routes . . . . . . . . . . . . . 13 78 2.5.2. Inter-AS I-PMSI A-D Routes . . . . . . . . . . . . . 13 79 2.6. S-PMSI A-D Routes . . . . . . . . . . . . . . . . . . . . 14 80 2.7. Leaf A-D Routes . . . . . . . . . . . . . . . . . . . . . 14 81 2.8. Source Active A-D Routes . . . . . . . . . . . . . . . . 14 82 2.8.1. Finding the Originator of an SA A-D Route . . . . . . 14 83 2.8.2. Optional Additional Constraints on Distribution . . . 15 84 2.9. C-multicast Source/Shared Tree Joins . . . . . . . . . . 16 85 3. Differences from other MVPN-like GTM Procedures . . . . . . . 16 86 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 87 5. Security Considerations . . . . . . . . . . . . . . . . . . . 17 88 6. Additional Contributors . . . . . . . . . . . . . . . . . . . 18 89 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 90 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 91 8.1. Normative References . . . . . . . . . . . . . . . . . . 19 92 8.2. Informative References . . . . . . . . . . . . . . . . . 19 93 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 95 1. Introduction 97 [RFC4364] specifies architecture, protocols, and procedures that a 98 Service Provider (SP) can use to provide Virtual Private Network 99 (VPN) service to its customers. In that architecture, one or more 100 Customer Edge (CE) routers attach to a Provider Edge (PE) router. 101 Each CE router belongs to a single VPN, but CE routers from several 102 VPNs may attach to the same PE router. In addition, CEs from the 103 same VPN may attach to different PEs. BGP is used to carry VPN- 104 specific information among the PEs. Each PE router maintains a 105 separate Virtual Routing and Forwarding table (VRF) for each VPN to 106 which it is attached. 108 [RFC6513] and [RFC6514] extend the procedures of [RFC4364] to allow 109 the SP to provide multicast service to its VPN customers. The 110 customer's multicast routing protocol (e.g., PIM) is used to exchange 111 multicast routing information between a CE and a PE. The PE stores a 112 given customer's multicast routing information in the VRF for that 113 customer's VPN. BGP is used to distribute certain multicast-related 114 control information among the PEs that attach to a given VPN, and BGP 115 may also be used to exchange the customer multicast routing 116 information itself among the PEs. 118 While this multicast architecture was originally developed for VPNs, 119 it can also be used (with a small number of modifications to the 120 procedures) to distribute multicast routing information that is not 121 specific to VPNs. The purpose of this document is to specify the way 122 in which BGP MVPN procedures can be adapted to support non-VPN 123 multicast. 125 Multicast routing information that is not specific to VPNs is stored 126 in a router's "global table", rather than in a VRF; hence it is known 127 as "Global Table Multicast" (GTM). GTM is sometimes more simply 128 called "Internet multicast". However, we will avoid that term 129 because it suggests that the multicast data streams are available on 130 the "public" Internet. The procedures for GTM can certainly be used 131 to support multicast on the public Internet, but they can also be 132 used to support multicast streams that are not public, e.g., content 133 distribution streams offered by content providers to paid 134 subscribers. For the purposes of this document, all that matters is 135 that the multicast routing information is maintained in a global 136 table rather than in a VRF. 138 This architecture does assume that the network over which the 139 multicast streams travel can be divided into a "core network" and one 140 or more non-core parts of the network, which we shall call 141 "attachment networks". The multicast routing protocol used in the 142 attachment networks may not be the same as the one used in the core, 143 so we consider there to be a "protocol boundary" between the core 144 network and the attachment networks. We will use the term "Protocol 145 Boundary Router" (PBR) to refer to the core routers that are at the 146 boundary. We will use the term "Attachment Router" (AR) to refer to 147 the routers that are not in the core but that attach to the PBRs. 149 This document does not make any particular set of assumptions about 150 the protocols that the ARs and the PBRs use to exchange unicast and 151 multicast routing information with each other. For instance, 152 multicast routing information could be exchanged between an AR and a 153 PBR via PIM, IGMP, or even BGP. Multicast routing also depends on an 154 exchange of routes that are used for looking up the path to the root 155 of a multicast tree. This routing information could be exchanged 156 between an AR and a PBR via IGP, via EBGP, or via IBGP ([RFC6368]). 157 Note that if IBGP is used, the [RFC6368] "push/pop procedures" are 158 not necessary. 160 The PBRs are not necessarily "edge" routers, in the sense of 161 [RFC4364]. For example, they may be both be Autonomous System Border 162 Routers (ASBR). As another example, an AR may be an "access router" 163 attached to a PBR that is an OSPF Area Border Router (ABR). Many 164 other deployment scenarios are possible. However, the PBRs are 165 always considered to be delimiting a "backbone" or "core" network. A 166 multicast data stream from an AR is tunneled over the core network 167 from an Ingress PBR to one or more Egress PBRs. Multicast routing 168 information that a PBR learns from the ARs attached to it is stored 169 in the PBR's global table. The PBRs use BGP to distribute multicast 170 routing and auto-discovery information among themselves. This is 171 done following the procedures of [RFC6513], [RFC6514], and other MVPN 172 specifications, as modified in this document. 174 In general, PBRs follow the same MVPN/BGP procedures that PE routers 175 follow, except that these procedures are adapted to be applicable to 176 the global table rather than to a VRF. Details are provided in 177 subsequent sections of this document. 179 By supporting GTM using the BGP procedures designed for MVPN, one 180 obtains a single control plane that governs the use of both VPN and 181 non-VPN multicast. Most of the features and characteristics of MVPN 182 carry over automatically to GTM. These include scaling, aggregation, 183 flexible choice of tunnel technology in the SP network, support for 184 both segmented and non-segmented tunnels, ability to use wildcards to 185 identify sets of multicast flows, support for the Any Source 186 Multicast (ASM), Single Source Multicast (SSM), and Bidirectional 187 (bidir) multicast paradigms, support for both IPv4 and IPv6 multicast 188 flows over either an IPv4 or IPv6 SP infrastructure, support for 189 unsolicited flooded data (including support for BSR as RP-to-group 190 mapping protocols), etc. 192 This document not only uses MVPN procedures for GTM, but also, 193 insofar as possible, uses the same protocol elements, encodings, and 194 formats. The BGP Updates for GTM thus use the same Subsequent 195 Address Family Identifier (SAFI), and have the same Network Layer 196 Reachability Information (NLRI) format, as the BGP Updates for MVPN. 198 Details for supporting MVPN (either IPv4 or IPv6 MVPN traffic) over 199 an IPv6 backbone network can be found in [RFC6515]. The procedures 200 and encodings described therein are also applicable to GTM. 202 The document [RFC7524] extends [RFC6514] by providing procedures that 203 allow tunnels through the core to be "segmented" at ABRs within the 204 core. The ABR segmentation procedures are also applicable to GTM as 205 defined in the current document. In general, the MVPN procedures of 206 [RFC7524], adapted as specified in the current document, are 207 applicable to GTM. 209 The document [RFC7524] also defines a set of procedures for GTM. 210 Those procedures are different from the procedures defined in the 211 current document, and the two sets of procedures are not 212 interoperable with each other. The two sets of procedures can co- 213 exist in the same network, as long as they are not applied to the 214 same multicast flows or to the same multicast group addresses. See 215 Section 3 for more details. 217 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 218 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 219 document are to be interpreted as described in [RFC2119]. 221 2. Adapting MVPN Procedures to GTM 223 In general, PBRs support Global Table Multicast by using the 224 procedures that PE routers use to support VPN multicast. For GTM, 225 where [RFC6513] and [RFC6514] talk about the "PE-CE interface", one 226 should interpret that to mean the interface between the AR and the 227 PBR. For GTM, where [RFC6513] and [RFC6514] talk about the 228 "backbone" network, one should interpret that to mean the part of the 229 network that is delimited by the PBRs. 231 A few adaptations to the procedures of [RFC6513] and [RFC6514] need 232 to be made. Those adaptations are described in the following sub- 233 sections. 235 2.1. Use of Route Distinguishers 237 The MVPN procedures require the use of BGP routes, defined in 238 [RFC6514], that have a SAFI value of 5 ("MCAST-VPN"). We refer to 239 these simply as "MCAST-VPN routes". [RFC6514] defines the Network 240 Layer Reachability Information (NLRI) format for MCAST-VPN routes. 241 The NLRI field always begins with a "Route Type" octet, and, 242 depending on the route type, may be followed by a "Route 243 Distinguisher" (RD) field. 245 When a PBR originates an MCAST-VPN route in support of GTM, the RD 246 field (for those routes types where it is defined) of that route's 247 NLRI MUST be set to zero (i.e., to 64 bits of zero). Since no VRF 248 may have an RD of zero, this allows "MCAST-VPN" routes that are 249 "about" GTM to be distinguished from MCAST-VPN routes that are about 250 VPNs. 252 2.2. Use of Route Targets 254 The MVPN procedures require all MCAST-VPN routes to carry Route 255 Targets (RTs). When a PE router receives an MCAST-VPN route, it 256 processes the route in the context of a particular VRF if and only if 257 the route is carrying an RT that is configured as one of that VRF's 258 "import RTs". 260 There are two different "kinds" of RT used in MVPN. 262 o One kind of RT is carried only by the following MCAST-VPN route 263 types: C-multicast Shared Tree Joins, C-multicast Source Tree 264 Joins, and Leaf A-D routes. This kind of RT identifies the PE 265 router that has been selected by the route's originator as the 266 "Upstream PE" or as the "Upstream Multicast Hop" (UMH) for a 267 particular (set of) multicast flow(s). Per [RFC6514] and 268 [RFC6515], this RT must be an IPv4-address-specific or IPv6- 269 address-specific Extended Community (EC), whose "Global 270 Administrator" field identifies the Upstream PE or the UMH. If 271 the Global Administrator field identifies the Upstream PE, the 272 "Local Administrator" field identifies a particular VRF in that 273 PE. 275 The GTM procedures of this document require the use of this type 276 of RT, in exactly the same situations where it is used in the MVPN 277 specification. However, one adaptation is necessary: the "Local 278 Administrator" field of this kind of RT MUST always be set to 279 zero, thus implicitly identifying the global table, rather than 280 identifying a VRF. We will refer to this kind of RT as an 281 "upstream-node-identifying RT". 283 o The other kind of RT is the conventional RT first specified in 284 [RFC4364]. It does not necessarily identify a particular router 285 by address, but is used to constrain the distribution of VPN 286 routes, and to ensure that a given VPN route is processed in the 287 context of a given VRF if and only if the route is carrying an RT 288 that has been configured as one of that VRF's "import RTs". 290 Whereas every VRF must be configured with at least one import RT, 291 there is heretofore no requirement to configure any RTs for the 292 global table of any router. As stated above, this document makes 293 the use of upstream-node-identifying RTs mandatory for GTM. This 294 document makes the use of non-upstream-node-identifying RTs 295 OPTIONAL for GTM. 297 The procedures for the use of RTs in GTM are the following: 299 o If the global table of a particular PBR is NOT configured with any 300 import RTs, then a received MCAST-VPN route is processed in the 301 context of the global table only if it is carrying no RTs, or if 302 it is carrying an upstream-node-identifying RT whose Global 303 Administrator field identifies that PBR. 305 o The global table in each PBR MAY be configured with (a) a set of 306 export RTs to be attached to MCAST-VPN routes that are originated 307 to support GTM, and (b) with a set of import RTs for GTM. 309 If the global table of a given PBR has been so configured, the PBR 310 will process a received MCAST-VPN route in the context of the 311 global table if and only if the route carries an RT that is one of 312 the global table's import RTs, or if the route carries an 313 upstream-node-identifying RT whose global administrator field 314 identifies the PBR. 316 If the global tables are configured with RTs, care must be taken 317 to ensure that the RTs configured for the global table are 318 distinct from any RTs used in support of MVPN (except in the case 319 where it is actually intended to create an "extranet" 320 [MVPN-extranet] in which some sources are reachable in global 321 table context while others are reachable in VPN context.) 323 The "RT Constraint" procedures of [RFC4684] MAY be used to constrain 324 the distribution of MCAST-VPN routes (or other routes) that carry RTs 325 that have been configured as import RTs for GTM. (This includes the 326 upstream-node-identifying RTs.) 328 N.B.: If the "RT Constraint" procedures of [RFC4684] are deployed, 329 but the MCAST-VPN routes are not carrying RTs, then proper 330 operation requires the "default behavior" specified for the 331 MCAST-VPN address family in Section 3 ("Default Behavior") of 332 [RTC_without_RTs]. 334 In [RFC6513], the UMH-eligible routes (see section 5.1 of [RFC6513], 335 "Eligible Routes for UMH Selection") are generally routes of SAFI 128 336 (Labeled VPN-IP routes) or 129 (VPN-IP multicast routes), and are 337 required to carry RTs. These RTs determine which VRFs import which 338 such routes. However, for GTM, when the UMH-eligible routes may be 339 routes of SAFI 1, 2, or 4, the routes are not required to carry RTs. 340 This document does NOT specify any new rules for determining whether 341 a SAFI 1, 2, or 4 route is to be imported into the global table of 342 any PBR. 344 2.3. UMH-eligible Routes 346 [RFC6513] section 5.1 defines procedures by which a PE router 347 determines the "C-root", the "Upstream Multicast Hop" (UMH), the 348 "Upstream PE", and the "Upstream RD" of a given multicast flow. (In 349 non-VPN multicast documents, the UMH of a multicast flow at a 350 particular router is generally known as the "RPF neighbor" for that 351 flow.) It also defines procedures for determining the "Source AS" of 352 a particular flow. Note that in GTM, the "Upstream PE" is actually 353 the "Upstream PBR". 355 The definition of the C-root of a flow is the same for GTM as for 356 MVPN. 358 For MVPN, to determine the UMH, Upstream PE, Upstream RD, and Source 359 AS of a flow, one looks up the C-root of the flow in a particular 360 VRF, and finds the "UMH-eligible" routes (see section 5.1.1 of 361 [RFC6513]) that "match" the C-root. From among these, one is chosen 362 as the "selected UMH route". 364 For GTM, the C-root is of course looked up in the global table, 365 rather than in a VRF. For MVPN, the UMH-eligible routes are routes 366 of SAFI 128 or 129. For GTM, the UMH-eligible routes are routes of 367 SAFI 1, SAFI 4, or SAFI 2. If the global table has imported routes 368 of SAFI 2, then these are the UMH-eligible routes. Otherwise, routes 369 of SAFI 1 or SAFI 4 are the UMH-eligible routes. For the purpose of 370 UMH determination, if a SAFI 1 route and a SAFI 4 route contain the 371 same IP prefix in their respective NLRI fields, then the two routes 372 are considered by the BGP bestpath selection process to be 373 comparable. 375 [RFC6513] defines procedures for determining which of the UMH- 376 eligible routes that match a particular C-root is to become the 377 "Selected UMH route". With one exception, these procedures are also 378 applicable to GTM. The one exception is the following. 379 Section 9.1.2 of [RFC6513] defines a particular method of choosing 380 the Upstream PE, known as "Single Forwarder Selection" (SFS). This 381 procedure MUST NOT be used for GTM (see Section 2.3.4 for an 382 explanation of why the SFS procedure cannot be applied to GTM). 384 In GTM, the "Upstream RD" of a multicast flow is always considered to 385 be zero, and is NOT determined from the Selected UMH route. 387 The MVPN specifications require that when BGP is used for 388 distributing multicast routing information, the UMH-eligible routes 389 MUST carry the VRF Route Import EC and the Source AS EC. To 390 determine the Upstream PE and Source AS for a particular multicast 391 flow, the Upstream PE and Source AS are determined, respectively, 392 from the VRF Route Import EC and the Source AS EC of the Selected UMH 393 route for that flow. These ECs are generally attached to the UMH- 394 eligible routes by the PEs that originate the routes. 396 In GTM, there are certain situations in which it is allowable to omit 397 the VRF Route Import EC and/or the Source AS EC from the UMH-eligible 398 routes. The following sub-sections specify the various options for 399 determining the Upstream PBR and the Source AS in GTM. 401 The procedures in Section 2.3.1 MUST be implemented. The procedures 402 in Section 2.3.2 and Section 2.3.3 are OPTIONAL to implement. It 403 should be noted that while the optional procedures may be useful in 404 particular deployment scenarios, there is always the potential for 405 interoperability problems when relying on OPTIONAL procedures. 407 2.3.1. Routes of SAFI 1, 2 or 4 with MVPN ECs 409 If the UMH-eligible routes have a SAFI of 1, 2 or 4, then they MAY 410 carry the VRF Route Import EC and/or the Source AS EC. If the 411 selected UMH route is a route of SAFI 1, 2 or 4 that carries the VRF 412 Route Import EC, then the Upstream PBR is determined from that EC. 413 Similarly, if the selected UMH route is a route of SAFI 1, 2, or 4 414 route that carries the Source AS EC, the Source AS is determined from 415 that EC. 417 When the procedure of this section is used, a PBR that distributes a 418 UMH-eligible route to other PBRs is responsible for ensuring that the 419 VRF Route Import and Source AS ECs are attached to it. 421 If the selected UMH-eligible route has a SAFI of 1, 2 or 4, but is 422 not carrying a VRF Route Import EC, then the Upstream PBR is 423 determined as specified in Section 2.3.2 or Section 2.3.3 below. 425 If the selected UMH-eligible route has a SAFI of 1, 2 or 4, but is 426 not carrying a Source AS EC, then the Source AS is considered to be 427 the local AS. 429 2.3.2. MVPN ECs on the Route to the Next Hop 431 Some service providers may consider it to be undesirable to have the 432 PBRs put the VRF Route Import EC on all the UMH-eligible routes. Or 433 there may be deployment scenarios in which the UMH-eligible routes 434 are not advertised by the PBRs at all. The procedures described in 435 this section provide an alternative that can be used under certain 436 circumstances. 438 The procedures of this section are OPTIONAL. 440 In this alternative procedure, each PBR MUST originate a BGP route of 441 SAFI 1, 2 or 4 to itself. This route MUST carry a VRF Route Import 442 EC that identifies the PBR. The address that appears in the Global 443 Administrator field of that EC MUST be the same address that appears 444 in the NLRI and in the Next Hop field of that route. This route MUST 445 also carry a Source AS EC identifying the AS of the PBR. 447 Whenever the PBR distributes a UMH-eligible route for which it sets 448 itself as next hop, it MUST use this same IP address as the Next Hop 449 of the UMH-eligible route that it used in the route discussed in the 450 prior paragraph. 452 When the procedure of his section is used, then when a PBR is 453 determining the Selected UMH Route for a given multicast flow, it may 454 find that the Selected UMH Route has no VRF Route Import EC. In this 455 case, the PBR will look up (in the global table) the route to the 456 Next Hop of the Selected UMH route. If the route to the Next Hop has 457 a VRF Route Import EC, that EC will be used to determine the Upstream 458 PBR, just as if the EC had been attached to the Selected UMH Route. 460 If recursive route resolution is required in order to resolve the 461 next hop, the Upstream PBR will be determined from the first route 462 with a VRF Route Import EC that is encountered during the recursive 463 route resolution process. (The recursive route resolution process 464 itself is not modified by this document.) 466 The same procedure can be applied to find the Source AS, except that 467 the Source AS EC is used instead of the VRF Route Import EC. 469 Note that this procedure is only applicable in scenarios where it is 470 known that the Next Hop of the UMH-eligible routes is not be changed 471 by any router that participates in the distribution of those routes; 472 this procedure MUST NOT be used in any scenario where the next hop 473 may be changed between the time one PBR distributes the route and 474 another PBR receives it. The PBRs have no way of determining 475 dynamically whether the procedure is applicable in a particular 476 deployment; this must be made known to the PBRs by provisioning. 478 Some scenarios in which this procedure can be used are: 480 o all PBRs are in the same AS, or 482 o the UMH-eligible routes are distributed among the PBRs by a Route 483 Reflector (that does not change the next hop), or 485 o the UMH-eligible routes are distributed from one AS to another 486 through ASBRs that do not change the next hop. 488 If the procedures of this section are used in scenarios where they 489 are not applicable, GTM will not function correctly. 491 2.3.3. Non-BGP Routes as the UMH-eligible Routes 493 In particular deployment scenarios, there may be specific procedures 494 that can be used, in those particular scenarios, to determine the 495 Upstream PBR for a given multicast flow. 497 Suppose the PBRs neither put the VRF Route Import EC on the UMH- 498 eligible routes, nor do they distribute BGP routes to themselves. It 499 may still be possible to determine the Upstream PBR for a given 500 multicast flow, using specific knowledge about the deployment. 502 For example, suppose it is known that all the PBRs are in the same 503 OSPF area. It may be possible to determine the Upstream PBR for a 504 given multicast flow by looking at the link state database to see 505 which router is attached to the flow's C-root. 507 As another example, suppose it is known that the set of PBRs is fully 508 meshed via Traffic Engineering (TE) tunnels. When a PBR looks up, in 509 its global table, the C-root of a particular multicast flow, it may 510 find that the next hop interface is a particular TE tunnel. If it 511 can determine the identify of the router at the other end of that TE 512 tunnel, it can deduce that that router is the Upstream PBR for that 513 flow. 515 This is not an exhaustive set of examples. Any procedure that 516 correctly determines the Upstream PBR in a given deployment scenario 517 MAY be used in that scenario. 519 2.3.4. Why SFS Does Not Apply to GTM 521 To see why the SFS procedure cannot be applied to GTM, consider the 522 following example scenario. Suppose some multicast source S is homed 523 to both PBR1 and PBR2, and suppose that both PBRs export a route (of 524 SAFI 1, 2, or 4) whose NLRI is a prefix matching the address of S. 525 These two routes will be considered comparable by the BGP decision 526 process. A route reflector receiving both routes may thus choose to 527 redistribute just one of the routes to S, the one chosen by the 528 bestpath algorithm. Different route reflectors may even choose 529 different routes to redistribute (i.e., one route reflector may 530 choose the route to S via PBR1 as the bestpath, while another chooses 531 the route to S via PBR2 as the bestpath). As a result, some PBRs may 532 receive only the route to S via PBR1 and some may receive only the 533 route to S via PBR2. In that case, it is impossible to ensure that 534 all PBRs will choose the same route to S. 536 The SFS procedure works in VPN context as along the following 537 assumption holds: if S is homed to VRF-x in PE1 and to VRF-y in PE2, 538 then VRF-x and VRF-y have been configured with different RDs. In VPN 539 context, the route to S is of SAFI 128 or 129, and thus has an RD in 540 its NLRI. So the route to S via PE1 will not have the same NLRI as 541 the route to S via PE2. As a result, all PEs will see both routes, 542 and the PEs can implement a procedure that ensures that they all pick 543 the same route to S. 545 That is, the SFS procedure of [RFC6513] relies on the UMH-eligible 546 routes being of SAFI 128 or 129, and relies on certain VRFs being 547 configured with distinct RDs. Thus the procedure cannot be applied 548 to GTM. 550 One might think that the SFS procedure could be applied to GTM as 551 long as the procedures defined in [ADD-PATH] are applied to the UMH- 552 eligible routes. Using the [ADD-PATH] procedures, the BGP speakers 553 could advertise more than one path to a given prefix. Typically 554 [ADD-PATH] is used to report the n best paths, for some small value 555 of n. However, this is not sufficient to support SFS, as can be seen 556 by examining the following scenario. 558 AS-X | AS-Y | AS-Z 559 | | 560 S--PBR1---ASBR1--|--ASBR2--|---ASBR5 561 | \______/ | | 562 | / \ | | 563 |--PBR2---ASBR3--|--ASBR4--|---ASBR6 564 | | 566 In AS-X, PBR1 reports to both ASBR1 and ASBR3 that it has a route to 567 S. Similarly, PBR2 reports to both ASBR1 and ASBR3 that it has a 568 route to S. Using [ADD-PATH], ASBR1 reports both routes to ASBR2, 569 and ASBR3 reports both routes to ASBR4. Now AS-Y sees 4 paths to S. 570 The AS-Z ASBRs will each see eight paths (four via ASBR2 and four via 571 ASBR4). To avoid this explosion in the number of paths, a BGP 572 speaker that uses [ADD-PATH] is usually considered to report only the 573 n best paths. However, there is then no guarantee that the reported 574 set of paths will contain at least one path via PBR1 and at least one 575 path via PBR2. Without such a guarantee, the SFS procedure will not 576 work. 578 2.4. Inclusive and Selective Tunnels 580 The MVPN specifications allow multicast flows to be carried on either 581 Inclusive Tunnels or on Selective Tunnels. When a flow is sent on an 582 Inclusive Tunnel of a particular VPN, it is sent to all PEs in that 583 VPN. When sent on a Selective Tunnel of a particular VPN, it may be 584 sent to only a subset of the PEs in that VPN. 586 This document allows the use of either Inclusive Tunnels or Selective 587 Tunnels for GTM. However, any service provider electing to use 588 Inclusive Tunnels for GTM should carefully consider whether sending a 589 multicast flow to ALL its PBRs would result in problems of scale. 590 There are potentially many more MBRs for GTM than PEs for a 591 particular VPN. If the set of PBRs is large and growing, but most 592 multicast flows do not need to go to all the PBRs, the exclusive use 593 of Selective Tunnels may be a better option. 595 2.5. I-PMSI A-D Routes 597 2.5.1. Intra-AS I-PMSI A-D Routes 599 Per [MVPN-BGP}, there are certain conditions under which is it NOT 600 required for a PE router implementing MVPN to originate one or more 601 Intra-AS I-PMSI A-D routes. These conditions apply as well to PBRs 602 implementing GTM. 604 In addition, a PBR implementing GTM is NOT required to originate an 605 Intra-AS I-PMSI A-D route if both of the following conditions hold: 607 o The PBR is not using Inclusive Tunnels for GTM, and 609 o The distribution of the C-multicast Shared Tree Join and 610 C-multicast Source Tree Join routes is done in such a manner that 611 the next hop of those routes does not change. 613 Please see also the sections on RD and RT usage. 615 2.5.2. Inter-AS I-PMSI A-D Routes 617 There are no GTM-specific procedures for the origination, 618 distribution, and processing of these routes, other than those 619 specified in the sections on RD and RT usage. 621 2.6. S-PMSI A-D Routes 623 There are no GTM-specific procedures for the origination, 624 distribution, and processing of these routes, other than those 625 specified in the sections on RD and RT usage. 627 2.7. Leaf A-D Routes 629 There are no GTM-specific procedures for the origination, 630 distribution, and processing of these routes, other than those 631 specified in the sections on RD and RT usage. 633 2.8. Source Active A-D Routes 635 Please see the sections on RD and RT usage for information applies to 636 the origination and distribution of Source Active A-D routes. 637 Additional procedures governing the use of Source Active A-D routes 638 are given in the sub-sections of this section. 640 2.8.1. Finding the Originator of an SA A-D Route 642 To carry out the procedures specified in [RFC6514] (e.g., in 643 Section 13.2 of that document), it is sometimes necessary for an 644 egress PE to determine the ingress PE that originated a given Source 645 Active A-D route. The procedure used in [RFC6514] to find the 646 originator of a Source Active A-D route assumes that no two routes 647 have the same RD unless they have been originated by the same PE. 648 However, this assumption is not valid in GTM, because each Source 649 Active A-D route used for GTM will have an RD of 0, and all the UMH- 650 eligible routes also have an RD of 0. So GTM requires a different 651 procedure for determining the originator of a Source Active A-D 652 route. 654 In GTM, the procedure for determining the originating PE of a Source 655 Active A-D route is the following: 657 o When a Source Active A-D route is originated, the originating PE 658 MAY attach a VRF Route Import Extended Community to the route. 660 o When a Source Active A-D route is distributed by one BGP speaker 661 to another, then 663 * if the Source Active A-D route does not carry the VRF Route 664 Import EC, the BGP speaker distributing the route MUST NOT 665 change the route's next hop field; 667 * if the Source Active A-D route does carry the VRF Route Import 668 EC, the BGP speaker distributing the route MAY change the 669 route's next hop field to itself. 671 o When an egress PE needs to determine the originator of a Source 672 Active A-D route, then 674 * if the Source Active A-D route carries the VRF Route Import EC, 675 the originating PE is the PE identified in the Global 676 Administrator field of that EC; 678 * if the Source Active A-D route does not carry the VRF Route 679 Import EC, the originating PE is the PE identified in the 680 route's next hop field. 682 2.8.2. Optional Additional Constraints on Distribution 684 If some site has receivers for a particular ASM group G, then it is 685 possible (by the procedures of [RFC6514]) that every PBR attached to 686 a site with a source for group G will originate a Source Active A-D 687 route whose NLRI identifies that source and group. These Source 688 Active A-D routes may be distributed to every PBR. If only a 689 relatively small number of PBRs are actually interested in traffic 690 from group G, but there are many sources for group G, this could 691 result in a large number of (S,G) Source Active A-D routes being 692 installed in a large number of PBRs that have no need of them. 694 For GTM, it is possible to constrain the distribution of (S,G) Source 695 Active A-D routes to those PBRs that are interested in GTM traffic to 696 group G. This can be done using the following OPTIONAL procedures: 698 o If a PBR originates a C-multicast Shared Tree Join whose NLRI 699 contains (RD=0,*,G), then it dynamically creates an import RT for 700 its global table, where the Global Administrator field of the RT 701 contains the group address G, and the Local Administrator field 702 contains zero. (Note that an IPv6-address-specific RT would need 703 to be used if the group address is an IPv6 address.) 705 o When a PBR creates such an import RT, it uses "RT Constraint" 706 [RFC4684] procedures to advertise its interest in routes that 707 carry this RT. 709 o When a PBR originates a Source Active A-D route from its global 710 table, it attaches the RT described above. 712 o When the C-multicast Shared Tree Join is withdrawn, so is the 713 corresponding RT constrain route, and the corresponding RT is 714 removed as an import RT of its global table. 716 These procedures enable a PBR to automatically filter all Source 717 Active A-D routes that are about multicast groups in which the PBR 718 has no interest. 720 This procedure does introduce the overhead of distributing additional 721 "RT Constraint" routes, and therefore may not be cost-effective in 722 all scenarios, especially if the number of sources per ASM group is 723 small. This procedure may also result in increased join latency. 725 2.9. C-multicast Source/Shared Tree Joins 727 [RFC6514] section 11.1.3 has the following procedure for determining 728 the IP-address-specific RT that is attached to a C-multicast route: 729 (a) determine the upstream PE, RD, AS, (b) find the proper Inter-AS 730 or Intra-AS I-PMSI A-D route based on (a), (c) find the next hop of 731 that A-D route, (d) base the RT on that next hop. 733 However, for GTM, in environments where it is known a priori that 734 that the next hop of the C-multicast Source/Shared Tree Joins does 735 not change during the distribution of those routes, the proper 736 procedure for creating the IP-address-specific RT is to just put the 737 IP Address of the Upstream PBR in the Global Administrator field of 738 the RT. In other scenarios, the procedure of the previous paragraph 739 (as modified by this document's sections on "RD usage" and "RT 740 usage") is applied by the PBRs. 742 3. Differences from other MVPN-like GTM Procedures 744 The document [RFC7524] also defines a procedure for GTM that is based 745 on the BGP procedures that were developed for MVPN. 747 However, the GTM procedures of [RFC7524] are different than and are 748 NOT interoperable with the procedures defined in this document. 750 The two sets of procedures can co-exist in the same network, as long 751 as they are not applied to the same multicast flows or to the same 752 ASM multicast group addresses. 754 Some of the major differences between the two sets of procedures are 755 the following: 757 o The [RFC7524] procedures for GTM do not use C-multicast Shared 758 Tree Joins or C-multicast Source Tree Joins at all. The 759 procedures of this document use these C-multicast routes for GTM, 760 setting the RD field of the NLRI to zero. 762 o The [RFC7524] procedures for GTM use Leaf A-D routes instead of 763 C-multicast Shared/Source Tree Join routes. Leaf A-D routes used 764 in that manner can be distinguished from Leaf A-D routes used as 765 specified in [RFC6514] by means of the NLRI format; [RFC7524] 766 defines a new NLRI format for Leaf A-D routes. Whether a given 767 Leaf A-D route is being used according to the [RFC7524] procedures 768 or not can be determined from its NLRI. (See [RFC7524] section 769 "Leaf A-D Route for Global Table Multicast".) 771 o The Leaf A-D routes used by the current document contain an NLRI 772 that is in the format defined in [RFC6514], NOT in the format as 773 defined in [RFC7524]. The procedures assumed by this document for 774 originating and processing Leaf A-D routes are as specified in 775 [RFC6514], NOT as specified in [RFC7524]. 777 o The current document uses an RD value of zero in the NLRI in order 778 to indicate that a particular route is "about" a Global 779 Table Multicast, rather than a VPN multicast. No other semantics 780 are inferred from the fact that RD is zero. [RFC7524] uses two 781 different RD values in its GTM procedures, with semantic 782 differences that depend upon the RD values. 784 o In order for both sets of procedures to co-exist in the same 785 network, the PBRs MUST be provisioned so that for any given IP 786 group address in the global table, all egress PBRs use the same 787 set of procedures for that group address (i.e., for group G, 788 either all egress PBRs use the GTM procedures of this document or 789 all egress PBRs use the GTM procedures of [RFC7524]. 791 4. IANA Considerations 793 This document has no IANA considerations. 795 5. Security Considerations 797 The security considerations of this document are primarily the 798 security considerations of the base protocols, as discussed in 799 [RFC6514], [RFC4601], and [RFC5294]. 801 This document makes use of a BGP SAFI (MCAST-VPN routes) that was 802 originally designed for use in VPN contexts only. It also makes use 803 of various BGP path attributes and extended communities (VRF Route 804 Import Extended Community, Source AS Extended Community, Route Target 805 Extended Community) that were originally intended for use in VPN 806 contexts. If these routes and/or attributes leak out into "the 807 wild", multicast data flows may be distributed in an unintended and/ 808 or unauthorized manner. 810 Internet providers often make extensive use of BGP communities (ie, 811 adding, deleting, modifying communities throughout a network). As 812 such, care should be taken to avoid deleting or modifying the VRF 813 Route Import Extended Community and Source AS Extended Community. 814 Incorrect manipulation of these ECs may result in multicast streams 815 being lost or misrouted. 817 The procedures of this document require certain BGP routes to carry 818 IP multicast group addresses. Generally such group addresses are 819 only valid within a certain scope. If a BGP route containing a group 820 address is distributed outside the boundaries where the group address 821 is meaningful, unauthorized distribution of multicast data flows may 822 occur. 824 6. Additional Contributors 826 Zhenbin Li 827 Huawei Technologies 828 Huawei Bld., No.156 Beiqing Rd. 829 Beijing 100095 830 China 831 Email: lizhenbin@huawei.com 833 Wei Meng 834 ZTE Corporation 835 No.50 Software Avenue, Yuhuatai District 836 Nanjing 837 China 838 Email: meng.wei2@zte.com.cn,vally.meng@gmail.com 840 Cui Wang 841 ZTE Corporation 842 No.50 Software Avenue, Yuhuatai District 843 Nanjing 844 China 845 Email: wang.cui1@zte.com.cn 847 Shunwan Zhuang 848 Huawei Technologies 849 Huawei Bld., No.156 Beiqing Rd. 850 Beijing 100095 851 China 852 Email: zhuangshunwan@huawei.com 854 7. Acknowledgments 856 The authors and contributors would like to thank Rahul Aggarwal, 857 Huajin Jeng, Hui Ni, Yakov Rekhter, and Samir Saad for their 858 contributions to this work. 860 8. References 862 8.1. Normative References 864 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 865 Requirement Levels", BCP 14, RFC 2119, March 1997. 867 [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private 868 Networks (VPNs)", RFC 4364, February 2006. 870 [RFC6513] Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP 871 VPNs", RFC 6513, February 2012. 873 [RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP 874 Encodings and Procedures for Multicast in MPLS/BGP IP 875 VPNs", RFC 6514, February 2012. 877 [RFC6515] Aggarwal, R. and E. Rosen, "IPv4 and IPv6 Infrastructure 878 Addresses in BGP Updates for Multicast VPN", RFC 6515, 879 February 2012. 881 8.2. Informative References 883 [ADD-PATH] 884 Walton, D., Retana, A., Chen, E., and J. Scudder, 885 "Advertisement of Multiple Paths in BGP", internet-draft 886 draft-ietf-idr-add-paths-10, October 2014. 888 [MVPN-extranet] 889 Rekhter, Y., Rosen, E., Aggarwal, R., Cai, Y., and T. 890 Morin, "Extranet Multicast in BGP/IP MPLS VPNs", internet- 891 draft draft-ietf-bess-mvpn-extranet-02, May 2015. 893 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 894 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 895 Protocol Specification (Revised)", RFC 4601, August 2006. 897 [RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk, 898 R., Patel, K., and J. Guichard, "Constrained Route 899 Distribution for Border Gateway Protocol/MultiProtocol 900 Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual 901 Private Networks (VPNs)", RFC 4684, November 2006. 903 [RFC5294] Savola, P. and J. Lingard, "Host Threats to Protocol 904 Independent Multicast (PIM)", RFC 5294, August 2008. 906 [RFC6368] Marques, P., Raszuk, R., Patel, K., Kumaki, K., and T. 907 Yamagata, "Internal BGP as the Provider/Customer Edge 908 Protocol for BGP/MPLS IP Virtual Private Networks (VPNs)", 909 RFC 6368, September 2011. 911 [RFC7524] Rekhter, Y., Rosen, E., Aggarwal, R., Morin, T., 912 Grosclaude, I., Leymann, N., and S. Saad, "Inter-Area 913 Point-to-Multipoint (P2MP) Segmented Label Switched Paths 914 (LSPs)", RFC 7524, May 2015. 916 [RTC_without_RTs] 917 Rosen, E., Ed., Patel, K., Haas, J., and R. Raszuk, "Route 918 Target Constrained Distribution of Routes with no Route 919 Targets", internet-draft draft-ietf-idr-rtc-no-rt-00, 920 January 2015. 922 Authors' Addresses 924 Zhaohui Zhang 925 Juniper Networks, Inc. 926 10 Technology Park Drive 927 Westford, Massachusetts 01886 928 US 930 Email: zzhang@juniper.net 932 Lenny Giuliano 933 Juniper Networks, Inc. 934 2251 Corporate Park Drive 935 Herndon, Virginia 20171 936 US 938 Email: lenny@juniper.net 940 Eric C. Rosen (editor) 941 Juniper Networks, Inc. 942 10 Technology Park Drive 943 Westford, Massachusetts 01886 944 US 946 Email: erosen@juniper.net 947 Karthik Subramanian 948 Cisco Systems, Inc. 949 170 Tasman Drive 950 San Jose, CA 95134 951 US 953 Email: kartsubr@cisco.com 955 Dante J. Pacella 956 Verizon 957 22001 Loudoun County Parkway 958 Ashburn, Virginia 95134 959 US 961 Email: dante.j.pacella@verizonbusiness.com 963 Jason Schiller 964 Google 965 Suite 400 966 1818 Library Street 967 Reston, Virginia 20190 968 US 970 Email: jschiller@google.com