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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-04) exists of draft-ietf-bess-mvpn-bidir-ingress-replication-00 == Outdated reference: A later version (-07) exists of draft-ietf-bess-mvpn-extranet-02 Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BESS Working Group E. Rosen, Ed. 3 Internet-Draft Juniper Networks, Inc. 4 Updates: 6513,6514 (if approved) K. Subramanian 5 Intended status: Standards Track Cisco Systems, Inc. 6 Expires: November 12, 2015 Z. Zhang 7 Juniper Networks, Inc. 8 May 11, 2015 10 Ingress Replication Tunnels in Multicast VPN 11 draft-ietf-bess-ir-01 13 Abstract 15 RFCs 6513, 6514, and other RFCs describe procedures by which a 16 Service Provider may offer Multicast VPN service to its customers. 17 These procedures create point-to-multipoint (P2MP) or multipoint-to- 18 multipoint trees across the Service Provider's backbone. One type of 19 P2MP tree that may be used is known as an "Ingress Replication (IR) 20 tunnel". In an IR tunnel, a parent node need not be "directly 21 connected" to its child nodes. When a parent node has to send a 22 multicast data packet to its child nodes, it does not use layer 2 23 multicast, IP multicast, or MPLS multicast to do so. Rather, it 24 makes n individual copies, and then unicasts each copy, through an IP 25 or MPLS unicast tunnel, to exactly one child node. While the prior 26 MVPN specifications allow the use of IR tunnels, those specifications 27 are not always very clear or explicit about how the MVPN protocol 28 elements and procedures are applied to IR tunnels. This document 29 updates RFCs 6513 and 6514 by adding additional details that are 30 specific to the use of IR tunnels. 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 12, 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 67 2. What is an IR P-tunnel? . . . . . . . . . . . . . . . . . . . 5 68 3. How are IR P-tunnels Identified? . . . . . . . . . . . . . . 6 69 4. How to Join an IR P-tunnel . . . . . . . . . . . . . . . . . 8 70 4.1. Advertised P-tunnels . . . . . . . . . . . . . . . . . . 9 71 4.1.1. If the 'Leaf Info Required Bit' is Set . . . . . . . 9 72 4.1.2. If the 'Leaf Info Required Bit' is Not Set . . . . . 10 73 4.2. Unadvertised P-tunnels . . . . . . . . . . . . . . . . . 10 74 5. The PTA's 'Tunnel Identifier' Field . . . . . . . . . . . . . 11 75 6. The PTA's 'MPLS Label' Field . . . . . . . . . . . . . . . . 11 76 6.1. Leaf A-D Route Originated by an Egress PE . . . . . . . . 12 77 6.2. Leaf A-D Route Originated by an Intermediate Node . . . . 14 78 6.3. Intra-AS I-PMSI A-D Route . . . . . . . . . . . . . . . . 15 79 7. How A Child Node Prunes Itself from an IR P-tunnel . . . . . 15 80 8. Parent Node Actions Upon Receiving Leaf A-D Route . . . . . . 16 81 9. Use of Timers when Switching UMH . . . . . . . . . . . . . . 17 82 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 83 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 84 12. Security Considerations . . . . . . . . . . . . . . . . . . . 18 85 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 86 13.1. Normative References . . . . . . . . . . . . . . . . . . 18 87 13.2. Informative References . . . . . . . . . . . . . . . . . 18 88 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 90 1. Introduction 92 RFCs 6513, 6514, and others describe procedures by which a Service 93 Provider (SP) may offer Multicast VPN (MVPN) service to its 94 customers. These procedures create point-to-multipoint (P2MP) or 95 multipoint-to-multipoint (MP2MP) tunnels, called "P-tunnels" 96 (Provider-tunnels), across the SP's backbone network. Customer 97 multicast traffic is carried through the P-tunnels. 99 A number of different P-tunnel technologies are supported. One of 100 the supported P-tunnel technologies is known as "ingress replication" 101 or "unicast replication". We will use the acronym "IR" to refer to 102 this P-tunnel technology. 104 An IR P-tunnel is a P2MP tree, but a given node on the tree is not 105 necessarily "directly attached" to its parent node or to its child 106 nodes. To send a multicast data packet from a parent node to one of 107 its child nodes, the parent node encapsulates the packet and then 108 unicasts it (through a P2P or MP2P MPLS LSP or a unicast IP tunnel) 109 to the child node. If a node on an IR tree has n child nodes, and 110 has a multicast data packet that must be sent along the tree, the 111 parent node makes n individual copies of the data packet, and then 112 sends each copy, through a unicast tunnel, to exactly one child node. 113 No lower layer multicast technology is used when sending traffic from 114 a parent node to a child node; multiple copies of the packet may 115 therefore be sent out a single interface. 117 With the single exception of IR, the P-tunnel technologies supported 118 by the MVPN specifications are pre-existing IP multicast or MPLS 119 multicast technologies. Each such technology has its own set of 120 specifications, its own setup and maintenance protocols, its own 121 syntax for identifying specific multicast trees, and its own 122 procedures for enabling a router to be added to or removed from a 123 particular multicast tree. For IR P-tunnels, on the other hand, 124 there is no prior specification for setting up and maintaining the 125 P2MP trees; the procedures and protocol elements used for setting up 126 and maintaining the P2MP trees are specified in the MVPN 127 specifications themselves, and all the signaling/setup is done by 128 using the BGP A-D (Auto-Discovery) routes that are defined in 129 [RFC6514]. (The unicast tunnels used to transmit multicast data from 130 one node to another in an IR P-tunnel may of course have their own 131 setup and maintenance protocols, e.g., [RFC5036], [RFC3209].) 133 Since the transmission of a multicast data packet along an IR 134 P-tunnel is done by transmitting the packet through a unicast tunnel, 135 previous RFCs sometimes speak of an IR P-tunnel as "consisting of" a 136 set of unicast tunnels. However, that way of speaking is not quite 137 accurate. For one thing, it obscures the fact that an IR P-tunnel is 138 really a P2MP tree, whose nodes must maintain multicast state in both 139 the control and data planes. For another, it obscures the fact the 140 unicast tunnels used by a particular IR P-tunnel need not be specific 141 to that P-tunnel; a single unicast tunnel can carry the multicast 142 traffic of many different IR P-tunnels (and can also carry unicast 143 traffic as well). 145 In this document, we provide a clearer and more explicit conceptual 146 model for IR P-tunnels, clarifying the relationship between an IR 147 P-tunnel and the unicast tunnels that are used for data transmission 148 along the IR P-tunnel. 150 RFC 6514 defines a protocol element called a "tunnel identifier", 151 which for most P-tunnel technologies is used to identify a P-tunnel 152 (i.e., to identify a P2MP or MP2MP tree). However, when IR P-tunnels 153 are used, this protocol element does not identify an IR P-tunnel. In 154 some cases it identifies one of the P-tunnel's constituent unicast 155 tunnels, and in other cases it is not used to identify a tunnel at 156 all. In this document, we provide an explicit specification for how 157 IR P-tunnels are actually identified. 159 Some of the MVPN specifications use phrases like "join the identified 160 P-tunnel", even though there has up to now not been an explicit 161 specification of how to identify an IR P-tunnel, of how a router 162 joins such a P-tunnel, or of how a router prunes itself from such a 163 P-tunnel. In this document, we make these procedures more explicit. 165 RFC 6514 does provide a method for binding an MPLS label to a 166 P-tunnel, but does not discuss the label allocation policies that are 167 needed for correct operation when the P-tunnel is an IR P-tunnel. 168 Those policies are discussed in this document. 170 This document does not provide any new protocol elements or 171 procedures; rather it makes explicit just how a router is to use the 172 protocol elements and procedures of [RFC6513] and [RFC6514] to 173 identify an IR P-tunnel, to join an IR P-tunnel, and to prune itself 174 from an IR P-tunnel. This document also discusses the MPLS label 175 allocation policies that need to be supported when binding MPLS 176 labels to IR P-tunnels, and the timer policies that need to be 177 supported when switching a customer multicast flow from one P-tunnel 178 to another. As the material in this document must be understood in 179 order to properly implement IR P-tunnels, this document is considered 180 to update [RFC6513] and [RFC6514]. This document also discusses the 181 application of "seamless multicast" [RFC7524] and "extranet" 182 [MVPN-XNET] procedures to IR P-tunnels. 184 This draft does not discuss the use of IR P-tunnels to support a VPN 185 customer's use of BIDIR-PIM. [C-BIDIR-IR] explains how to adapt the 186 procedures of [RFC6513], [RFC6514], and [MVPN-BIDIR] so that a 187 customer's use of BIDIR-PIM can be supported by IR P-tunnels. 189 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 190 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 191 "OPTIONAL", when and only when appearing in all capital letters, are 192 to be interpreted as described in [RFC2119]. 194 2. What is an IR P-tunnel? 196 An IR P-tunnel is a P2MP tree. Its nodes are BGP speakers that 197 support the MVPN procedures of [RFC6514] and related RFCs. In 198 general, the nodes of an IR P-tunnel are either PE routers, ASBRs, or 199 (if [RFC7524] is supported) ABRs. (MVPN procedures are sometimes 200 used to support non-MVPN, or "global table" multicast; one way of 201 doing this is defined in [RFC7524]. In such a case, IR P-tunnels can 202 be used outside the context of MVPN.) 204 MVPN P-tunnels may be either "segmented" or "non-segmented" (as these 205 terms are defined in [RFC6513] and [RFC6514]). 207 A "non-segmented" IR P-tunnel is a two-level P2MP tree, consisting 208 only of a root node and a set of nodes that are children of the root 209 node. When used in an MVPN context, the root is an ingress PE, and 210 the child nodes of the root are the egress PEs. 212 In a segmented P-tunnel, IR may be used for some or all of the 213 segments. If a particular segment of a segmented P-tunnel uses IR, 214 then the root of that segment may have child nodes that are ABRs or 215 ASBRs, rather than egress PEs. 217 As with any type of P2MP tree, each node of an IR P-tunnel holds 218 "multicast state" for the P-tunnel. That is, each node knows the 219 identity of its parent node on the tree, and each node knows the 220 identities of its child nodes on the tree. In the MVPN specs, the 221 "parent" node is also known as the "Upstream Multicast Hop" or "UMH". 222 Note that the "UMH" may be a PE, an ASBR, or (if procedures from 223 [RFC7524] are being used) an ABR. (In [RFC7524], the term "upstream 224 node" is used instead of "UMH".) 226 What distinguishes an IR P-tunnel from any other kind of P2MP tree is 227 the method by which a data packet is transmitted from a parent node 228 to a child node. To transmit a multicast data packet from a parent 229 node to a child node along a particular IR P-tunnel, the parent node 230 does the following: 232 o It labels the packet with a label (call it a "P-tunnel label") 233 that the child node has assigned to that P-tunnel, 235 o It then places the packet in a unicast encapsulation and unicasts 236 the packet to the child node. That is, the parent node sends the 237 packet through a "unicast tunnel" to a particular child node. 238 This unicast tunnel need not be specially created to be part of 239 the IR P-tunnel; it can be any P2P or MP2P unicast tunnel that 240 will get the packets from the parent node to the child node. A 241 single such unicast tunnel may be carrying multicast data packets 242 of several different P2MP trees, and may also be carrying unicast 243 data packets. 245 The parent node repeats this process for each child node, creating 246 one copy for each child node, and sending each copy through a unicast 247 tunnel to corresponding child node. It does not use layer 2 248 multicast, IP multicast, or MPLS multicast to transmit packets to its 249 child nodes. As a result, multiple copies of each packet may be sent 250 out a single interface; this may happen, e.g., if that interface is 251 the next hop interface, according to unicast routing, from the parent 252 node to several of the child nodes. 254 Since data traveling along an IR P-tunnel is always unicast from 255 parent node to child node, it can be convenient to think of an IR 256 P-tunnel as a P2MP tree whose arcs are unicast tunnels. However, it 257 is important to understand that the unicast tunnels need not be 258 specific to any particular IR P-tunnel. If R1 is the parent node of 259 R2 on two different IR P-tunnels, a single unicast tunnel from R1 to 260 R2 may be used to carry data along both IR P-tunnels. All that is 261 required is that when the data packets arrive at R2, R2 will see the 262 "P-tunnel label" at the top of the packets' label stack; R2's further 263 processing of the packets will depend upon that label. Note that the 264 same unicast tunnel between R1 and R2 may also be carrying unicast 265 data packets. 267 Typically the unicast tunnels are the Label Switched Paths (LSPs) 268 that already exist to carry unicast traffic; either MP2P LSPs created 269 by LDP [RFC5036] or P2P LSPs created by RSVP-TE [RFC3209]. However, 270 any other kind of unicast tunnel may be used. A unicast tunnel may 271 have an arbitrary number of intermediate routers; those routers do 272 not maintain any multicast state for the IR P-tunnel, and in general 273 are not even aware of its existence. 275 As with all other P-tunnel types, IR P-tunnels may be used as 276 Inclusive P-tunnels or as Selective P-tunnels. 278 3. How are IR P-tunnels Identified? 280 There are four MVPN BGP route types in which P-tunnels can be 281 identified: Intra-AS I-PMSI A-D routes, Inter-AS I-PMSI A-D routes, 282 S-PMSI A-D routes, and Leaf A-D routes. (These route types are all 283 defined in [RFC6514]). 285 Whenever it is necessary to identify a P-tunnel in a route of one of 286 these types, a "PMSI Tunnel Attribute" (PTA) is added to the route. 287 As defined in [RFC6514] section 5, the PTA contains four fields: 288 "Tunnel Type", "MPLS Label", "Tunnel Identifier", and "Flags". 290 [RFC6514] defines only one bit in the "Flags" field, the "Leaf 291 Information Required" bit. 293 If a route identifies an IR P-tunnel, the "Tunnel Type" field of its 294 PTA is set to the value 6, meaning "Ingress Replication". 296 Most types of P-tunnel are associated with specific protocols that 297 are used to set up and maintain tunnels of that type. For example, 298 if the "Tunnel Type" field is set to 2, meaning "mLDP P2MP LSP", the 299 associated setup protocol is mLDP [RFC6388]. The associated setup 300 protocol always has a method of identifying the tunnels that it sets 301 up. For example, mLDP uses a "FEC element" to identify a tree. If 302 the "Tunnel type" field is set to 3, meaning "PIM SSM Tree", the 303 associated setup protocol is PIM, and "(S,G)" is used to identify the 304 tree. In these cases, the "Tunnel Identifier" field of the PTA 305 carries a tree identifier as defined by the setup protocol used for 306 the particular tunnel type. 308 IR P-tunnels, on the other hand, are entirely setup and maintained by 309 the use of BGP A-D routes, and are not associated with any other 310 setup protocol. (The unicast tunnels used to transmit multicast data 311 along an IR P-tunnel may have their own setup and maintenance 312 protocols, of course.) Further, the identifier of an IR P-tunnel 313 does not appear in the PTA at all. Rather, the P-tunnel identifier 314 is in the "Network Layer Reachability Information" (NLRI) field of 315 the A-D routes that are used to advertise and to setup the P-tunnel. 317 When an IR P-tunnel is identified in an S-PMSI A-D route, an Intra-AS 318 I-PMSI A-D route, or an Inter-AS I-PMSI A-D route (we will refer to 319 these three route types as "advertising A-D routes"), its identifier 320 is hereby defined to be the NLRI of that route. See sections 4.1, 321 4.2, and 4.3 of [RFC6514] for the specification of these NLRIs. Note 322 that the P-tunnel identifier includes the "route type" and "length" 323 octets of the NLRI. 325 An advertising A-D route is considered to identify an IR P-tunnel 326 only if it carries a PTA whose "Tunnel Type" field is set to "IR". 328 When an IR P-tunnel is identified in an S-PMSI A-D route or in an 329 Inter-AS I-PMSI A-D route, the "Leaf Info Required" bit of the Flags 330 field of the PTA MUST be set. 332 In an advertising A-D route: 334 o If the "Leaf Info Required" bit of the Flags field of the PTA is 335 set, then the "Tunnel Identifier" field of the PTA has no 336 significance whatsoever, and MUST be ignored upon reception. 338 Note that, per RFC6514, the length of the "Tunnel Identifier" 339 field is variable, and is inferred from the length of the PTA. 340 Even when this field is of no significance, its length MUST be the 341 length of an IP address in the address space of the SP's backbone, 342 as specified in section 4.2 of [RFC6515]. In this case, it is 343 RECOMMENDED that it be set to a routable address of the router 344 that constructed the PTA. (While it might make more sense to 345 allow or even require the field to be omitted entirely, that might 346 raise issues of backwards compatibility with implementations that 347 were designed prior to the publication of this document.) 349 o If the "Leaf Info Required" bit is not set, the "Tunnel 350 Identifier" field of the PTA does have significance, but it does 351 not identify the IR P-tunnel. The use of the PTA's "Tunnel 352 Identifier" field in this case is discussed in Section 5 of this 353 document. 355 Note that according to the above definition, there is no way for two 356 different advertising A-D routes (i.e., two advertising A-D routes 357 with different NLRIs) to advertise the same IR P-tunnel. In the 358 terminology of [RFC6513], an IR P-tunnel can instantiate only a 359 single PMSI. If an ingress PE, for example, wants to bind two 360 customer multicast flows to a single IR P-tunnel, it must advertise 361 that tunnel in an I-PMSI A-D route or in an S-PMSI A-D route whose 362 NLRI contains wildcards ([RFC6625]). 364 When an IR P-tunnel is identified in a Leaf A-D route, its identifier 365 is the "route key" field of the route's NLRI. See section 4.4 of 366 [RFC6514]. 368 A Leaf A-D route is considered to identify an IR P-tunnel only if it 369 carries a PTA whose "Tunnel Type" field is set to "IR". In this type 370 of route, the "Tunnel Identifier" field of the PTA does have 371 significance, but it does not identify the IR P-tunnel. The use of 372 the PTA's "Tunnel Identifier" field in this case is discussed in 373 Section 5. 375 4. How to Join an IR P-tunnel 377 The procedures for joining an IR P-tunnel depend upon whether the 378 P-tunnel has been previously advertised, and if so, upon how the 379 P-tunnel was advertised. Note that joining an unadvertised P-tunnel 380 is only possible when using the "Global Table Multicast" procedures 381 of [RFC7524]. 383 4.1. Advertised P-tunnels 385 The procedures in this section apply when the P-tunnel to be joined 386 has been advertised in an S-PMSI A-D route, an Inter-AS I-PMSI A-D 387 route, or an Intra-AS I-PMSI A-D route. 389 The procedures for joining an advertised IR P-tunnel depend upon 390 whether the A-D route that advertises the P-tunnel has the "Leaf Info 391 Required" bit set in its PTA. 393 4.1.1. If the 'Leaf Info Required Bit' is Set 395 The procedures in this section apply when the P-tunnel to be joined 396 has been advertised in a route whose PTA has the "Leaf Info Required 397 Bit" set. 399 The router joining a particular IR P-tunnel must determine its UMH 400 for that P-tunnel. If the route that advertised the P-tunnel 401 contains a P2MP Segmented Next Hop Extended Community, the UMH is 402 determined from the value of this community (see [RFC7524]). 403 Otherwise the UMH is determined from the route's next hop (see 404 [RFC6514]). 406 Once the UMH is determined, the router joining the IR P-tunnel 407 originates a Leaf A-D route. The NLRI of the Leaf A-D route MUST 408 contain the tunnel identifier (as defined in Section 3 above) as its 409 "route key". The UMH MUST be identified by attaching an "IP Address 410 Specific Route Target" (or an "IPv6 Address Specific Route Target") 411 to the Leaf A-D route. The IP address of the UMH appears in the 412 "global administrator" field of the Route Target (RT). Details can 413 be found in [RFC6514] and [RFC7524]. 415 The Leaf A-D route MUST also contain a PTA whose fields are set as 416 follows: 418 o The "Tunnel Type" field is set to "IR". 420 o The "Tunnel Identifier" field is set as described in Section 5 of 421 this document. 423 o The "MPLS Label" field is set to a non-zero value. This is the 424 "P-tunnel label". The value must be chosen so as to satisfy 425 various constraints, as discussed in Section 6 this document. 427 4.1.2. If the 'Leaf Info Required Bit' is Not Set 429 The procedures in this section apply when the P-tunnel to be joined 430 has been advertised in a route whose PTA does not have the "Leaf Info 431 Required Bit" set. This can only be the case if the P-tunnel was 432 advertised in an Intra-AS I-PMSI A-D route. 434 If an IR P-tunnel is advertised in the Intra-AS I-PMSI A-D routes 435 originated by the PE routers of a given MVPN, the Intra-AS I-PMSI can 436 be thought of as being instantiated by a set of IR P-tunnels. Each 437 PE is the root of one such P-tunnel, and the other PEs are children 438 of the root. A PE simultaneously joins all these P-tunnels by 439 originating (if it hasn't already done so) an Intra-AS I-PMSI A-D 440 route with a PTA whose fields are set as follows: 442 o The "Tunnel Type" field is set to "IR". 444 o The "Tunnel Identifier" field is set as described in Section 5 of 445 this document. 447 o The "MPLS Label" field MUST be set to a non-zero value. This 448 label value will be used by the child node to associate a received 449 packet with the I-PMSI of a particular MVPN. The MPLS label 450 allocation policy must be such as to ensure that the binding from 451 label to I-PMSI is one-to-one. 453 The NLRI and the RTs of the originated I-PMSI A-D route are set as 454 specified in [RFC6514]. 456 Note that if a set of IR P-tunnels is joined in this manner, the 457 "discard from the wrong PE" procedures of [RFC6513] section 9.1.1 458 cannot be applied to that P-tunnel. Thus duplicate prevention on 459 such IR P-tunnels requires the use of either Single Forwarder 460 Selection ([RFC6513] section 9.1.2) or native PIM procedures 461 ([RFC6513] section 9.1.3). 463 4.2. Unadvertised P-tunnels 465 In [RFC7524], a procedure is defined for "Global Table Multicast", in 466 which a P-tunnel can be joined even if the P-tunnel has not been 467 previously advertised. See the sections of that document entitled 468 "Leaf A-D Route for Global Table Multicast" and "Constructing the 469 Rest of the Leaf A-D Route". The route key of the Leaf A-D route has 470 the form of the "S-PMSI Route-Type Specific NLRI" in this case, and 471 that should be considered to be the P-tunnel identifier. Note that 472 the procedure for finding the UMH is different in this case; the UMH 473 is the next hop of the best UMH-eligible route towards the "ingress 474 PE". See the section of that document entitled "Determining the 475 Upstream ABR/PE/ASBR (Upstream Node)". 477 5. The PTA's 'Tunnel Identifier' Field 479 If the "Tunnel Type" field of a PTA is set to "IR", its "Tunnel 480 Identifier" field is significant only when one of the following two 481 conditions holds: 483 o The PTA is carried by a Leaf A-D route, or 485 o The "Leaf Information Required" bit of the "Flags" field of the 486 PTA is not set. 488 If one of these conditions holds, then the "Tunnel Identifier" field 489 must contain a routable IP address of the originator of the route. 490 (See [RFC6514] sections 9.2.3.2.1 and 9.2.3.4.1 for the detailed 491 specification of the contents of this field.) This address is used 492 by the UMH to determine the unicast tunnel that it will use in order 493 to send data, along the IR P-tunnel identified by the route key, to 494 the originator of the Leaf A-D route. 496 The means by which the unicast tunnel is determined from this IP 497 address is outside the scope of this document. The means by which 498 the unicast tunnel is set up and maintained is also outside the scope 499 of this document. 501 Section 4 of [RFC6515] MUST be applied when a PTA is carried in a 502 Leaf A-D route, and describes how to determine whether the "Tunnel 503 Identifier" field carries an IPv4 or an IPv6 address. 505 If neither of the above conditions hold, then the "Tunnel Identifier" 506 field is of no significance, and MUST be ignored upon reception. 508 6. The PTA's 'MPLS Label' Field 510 When the "Tunnel Type" field of a PTA is set to "IR", the "MPLS 511 Label" field is not always significant. It is significant only under 512 the following conditions: 514 1. Either the PTA is being carried in a Leaf A-D route, or 516 2. the "Leaf Information Required" flag of the PTA is NOT set. 518 Note that the "Leaf Information Required" flag of the PTA is always 519 set when a PTA specifying an IR tunnel is carried in an S-PMSI A-D 520 route or in an Inter-AS I-PMSI A-D route; thus the "MPLS Label" field 521 of the PTA is never significant when the PTA is carried by one of 522 these route types. The "MPLS Label" field is significant only when 523 the PTA appears either in a Leaf A-D route or in an Intra-AS I-PMSI 524 A-D route that does not have the "Leaf Information Required" bit set. 525 In these cases, the MPLS label is the label that the originator of 526 the route is assigning to the IR P-tunnel(s) identified by the 527 route's NLRI. (That is, the MPLS label assigned in the PTA is what 528 we have called the "P-tunnel label".) 530 In those cases where the "MPLS Label" field is not significant, it 531 SHOULD be set to zero upon transmission and MUST be ignored upon 532 reception. 534 6.1. Leaf A-D Route Originated by an Egress PE 536 As previously stated, when a Leaf A-D route is used to join an IR 537 P-tunnel, the "route key" of the Leaf A-D route is the P-tunnel 538 identifier. 540 We now define the notion of the "root of an IR P-tunnel". 542 o If the identifier of an IR P-tunnel is of the form of an S-PMSI 543 NLRI, the "root" of the P-tunnel is the router identified in the 544 "Originating Router's IP Address" field of that NLRI. 546 o If the identifier of an IR P-tunnel is of the form specified in 547 Section "Leaf A-D Route for Global Table Multicast" of [RFC7524], 548 the "root" of the P-tunnel is the router identified in the 549 "Ingress PE's IP Address" field of that NLRI. 551 o If the identifier of an IR P-tunnel is of the form of an Intra-AS 552 I-PMSI NLRI, the "root" of the P-tunnel is the router identified 553 in the "Originating Router's IP Address" field of that NLRI. 555 o If the identifier of an IR P-tunnel is of the form of an Inter-AS 556 I-PMSI NLRI, the "root" of the P-tunnel is same as the identifier 557 of the P-tunnel, i.e., the combination of an RD and an AS. 559 Note that if a P-tunnel is segmented, the root of the P-tunnel, by 560 this definition, is actually the root of the entire P-tunnel, not the 561 root of the local segment. In this case, there may be segments 562 upstream that are not themselves IR P-tunnels. However, the egress 563 PE is aware only of the final segment of the P-tunnel, and hence 564 considers the P-tunnel to be an IR P-tunnel. 566 In order to apply the procedures of RFC 6513 Section 9.1.1 567 ("Discarding Packets from Wrong PE"), the following condition MUST be 568 met by the MPLS label allocation policy: 570 Suppose an egress PE originates two Leaf A-D routes, each with a 571 different route key in its NLRI, and each with a PTA specifying a 572 "Tunnel Type" of "IR". Thus each of the Leaf A-D routes 573 identifies a different IR P-tunnel. Suppose further that each of 574 those IR P-tunnels has a different root. Then the egress PE MUST 575 NOT specify the same MPLS label in both PMSI Tunnel attributes. 577 That is, to apply the "Discarding Packets from the Wrong PE" 578 duplicate prevention procedures ([RFC6513] section 9.1.1), the same 579 MPLS label MUST NOT be assigned to two IR P-tunnels that have 580 different roots. 582 If segmented P-tunnels are in use, the above rule is necessary but 583 not sufficient to prevent a PE from forwarding duplicate data to the 584 CEs. For various reasons, a given egress PE or egress ABR or egress 585 ASBR may decide to change its parent node, on a given segmented 586 P-tunnel, from one router to another. It does this by changing the 587 RT of the Leaf A-D route that it originated in order to join that 588 P-tunnel. Once the RT is changed, there may be a period of time 589 during which the old parent node and the new parent node are both 590 sending data of the same multicast flow. To ensure that the egress 591 node not forward duplicate data, whenever the egress node changes the 592 RT that it attaches to a Leaf A-D route, it MUST also change the 593 "MPLS Label" specified in the Leaf A-D route's PTA. This allows the 594 egress router to distinguish between packets arriving on a given 595 P-tunnel from the old parent and packets arriving on that same 596 P-tunnel from the new parent. At any given time, a router MUST 597 consider itself to have only a single parent node on a given 598 P-tunnel, and MUST discard traffic that arrives on that P-tunnel from 599 a different parent node. 601 If extranet functionality [MVPN-XNET] is not implemented in a 602 particular egress PE, or if an egress PE is provisioned with the 603 knowledge that extranet functionality is not needed, the PE may adopt 604 the policy of assigning a label that is unique for the ordered triple 605 . This will enable the egress PE to 606 apply the duplicate prevention procedures discussed above, and to 607 determine the VRF to which an arriving packet must be directed. 609 However, this policy is not sufficient to support the "Discard 610 Packets from the Wrong P-tunnel" procedures that are specified in 611 [MVPN-XNET]. To support those procedures, the labels specified in 612 the PTA of Leaf A-D routes originated by a given egress PE MUST be 613 unique for the ordered triple , where the 614 "root RD" is taken from the RD field of the IR P-tunnel identifier. 615 (All forms of IR P-tunnel identifier contain an embedded "RD" field.) 616 This policy is also sufficient for supporting non-extranet cases, but 617 in some cases may result in the use of more labels than the policy of 618 the previous paragraph. 620 6.2. Leaf A-D Route Originated by an Intermediate Node 622 When a P-tunnel is segmented, there will be "intermediate nodes", 623 i.e., nodes that have a parent and also have children on the 624 P-tunnel. Each intermediate node is a leaf node of an "upstream 625 segment" and a parent node of one or more "downstream segments". The 626 intermediate node needs to set up its forwarding state so that data 627 it receives on the upstream segment gets transmitted on the proper 628 downstream segments. 630 If the upstream segment is instantiated by IR, the intermediate node 631 will need to originate a Leaf A-D route to join that segment, and 632 will need to allocate a downstream-assigned MPLS label to advertise 633 in the MPLS label field of the Leaf A-D route's PTA. Section 6.1 634 specifies constraints on the label allocation policy for egress PEs; 635 this section specifies constraints on the label allocation policy for 636 intermediate nodes. 638 Suppose intermediate node N originates two Leaf A-D routes, one whose 639 route key is K1, and one whose route key is K2, where K1 != K2. The 640 respective PTAs of these Leaf A-D routes MUST specify distinct non- 641 zero MPLS labels, UNLESS the following conditions all hold: 643 1. N's parent node for P-tunnel K1 is the same as N's parent node 644 for P-tunnel K2. 646 2. N's forwarding state is such that any packet it receives from 647 P-tunnel K1 is forwarded to the exact same set of downstream 648 neighbors as any packet it receives from P-tunnel K2. 650 3. For each downstream neighbor D to which N sends the packets it 651 receives from P-tunnels K1 and K2, N's forwarding state is such 652 that it applies the exact same encapsulation to packets it 653 forwards from either tunnel to D. (E.g., if N uses MPLS to 654 forward the packets to D, it pushes the exact same set of labels 655 on packets from P-tunnel K1 as it pushes on packets from P-tunnel 656 K2.) 658 Of course, N MAY always specify distinct non-zero labels in each of 659 the Leaf A-D routes that it originates. 661 Note that the rules of this section apply whenever the upstream 662 P-tunnel segment is an IR P-tunnel. These rules hold whether or not 663 some or all of the downstream segments are other types of P-tunnels. 665 If the P-tunnels from N to a particular downstream neighbor D are IR 666 P-tunnels, then condition 3 above will hold with respect to D only if 667 the following conditions all hold as well: 669 o N has received and installed a Leaf A-D route from D, whose route 670 key is K1, and which carries an IP-address-specific RT identifying 671 N, 673 o N has received and installed a Leaf A-D route from D, whose route 674 key is K2, and which carries an IP-address-specific RT identifying 675 N, 677 o Those two Leaf A-D routes specify the same MPLS label in their 678 respective PTAs. 680 6.3. Intra-AS I-PMSI A-D Route 682 When a router joins a set of IR P-tunnels using the procedures of 683 Section 4.1.2 of this document, the procedures of section 9.1.1 of 684 [RFC6513] cannot be applied, no matter what the label allocation 685 policy is. In this case, the ingress PE is the same as the UMH, but 686 it is not possible to assign a label uniquely to a particular ingress 687 PE or UMH. However, the label in the MPLS label field of the PTA 688 MUST NOT appear in the MPLS label field of the PTA carried by any 689 other route originated by the same router. 691 7. How A Child Node Prunes Itself from an IR P-tunnel 693 If a particular IR P-tunnel was joined via the procedures of 694 Section 4.1.2 of this document, a router can prune itself from the 695 P-tunnel by withdrawing the Intra-AS I-PMSI A-D route it used to join 696 the P-tunnel. This is not usually done unless the router is removing 697 itself entirely from a particular MVPN. 699 The procedures in the remainder of this section apply when a router 700 joined a particular IR P-tunnel by originating a Leaf A-D route (as 701 described in Section 4.1.1 or Section 4.2 of this document). 703 If a router no longer has a need to receive any multicast data from a 704 given IR P-tunnel, it may prune itself from the P-tunnel by 705 withdrawing the Leaf A-D route it used to join the tunnel. This is 706 done, e.g., if the router no longer needs any of the flows traveling 707 over the P-tunnel, or if all the flows the router does need are being 708 received over other P-tunnels. 710 A router that is attached to a particular IR P-tunnel via a 711 particular parent node may determine that it needs to stay joined to 712 that P-tunnel, but via a different parent node. This can happen, for 713 example, if there is a change in the Next Hop or the P2MP Segmented 714 Next Hop Extended Community of the S-PMSI A-D route in which that 715 P-tunnel was advertised. In this case, the router changes the Route 716 Target of the Leaf A-D route it used to join the IR P-tunnel, so that 717 the Route Target now identifies the new parent node. 719 A parent node must notice when a child node has been pruned from a 720 particular tree, as this will affect the parent node's multicast data 721 state. Note that the pruning of a child node may appear to the 722 parent node as the explicit withdrawal of a Leaf A-D route, or it may 723 appear as a change in the Route Target of a Leaf A-D route. If the 724 Route Target of a particular Leaf A-D route previously identified a 725 particular parent node, but changes so that it no longer does so, the 726 effect on the multicast state of the parent node is the same as if 727 the Leaf A-D route had been explicitly withdrawn. 729 8. Parent Node Actions Upon Receiving Leaf A-D Route 731 These actions are detailed in [RFC6514] and [RFC7524]. Two points of 732 clarification are made: 734 o If a router R1 receives and installs a Leaf A-D route originated 735 by router R2, R1's multicast state is affected only if the Leaf 736 A-D route carries an "IP Address Specific RT" (or "IPv6 Address 737 Specific RT") whose "global administrator" field identifies R1. 739 (This is as specified in [RFC6514] and [RFC7524].) If a Leaf A-D 740 route's RT does not identify R1, but then changes so that it does 741 identify R1, R1 must take the same actions it would take if the 742 Leaf A-D route were newly received. 744 o It is possible that router R1 will receive and install a Leaf A-D 745 route originated by router R2, where: 747 * the route's RT identifies R1, 749 * the route's NLRI contains a route key whose first octet 750 indicates that it is identifying a P-tunnel advertised in an 751 S-PMSI A-D route, 753 * R1 has neither originated nor installed any such S-PMSI A-D 754 route. 756 If at some later time, R1 installs the corresponding S-PMSI A-D 757 route, and the Leaf A-D route is still installed, and the Leaf A-D 758 route's RT still identifies R1, then R1 MUST follow the same 759 procedures it would have followed if the S-PMSI A-D route had been 760 installed before the Leaf A-D route was installed. (I.e., 761 implementers must not assume that events occur in the "usual" or 762 "expected" order.) 764 9. Use of Timers when Switching UMH 766 Suppose a child node has joined a particular IR P-tunnel via a 767 particular UMH, and it now determines (for whatever reason) that it 768 needs to change its UMH on that P-tunnel. It does this by modifying 769 the RT of a Leaf A-D route. 771 It is desirable for such a "switch of UMH" to be done using a "make 772 before break" technique, so that the older UMH does not stop 773 transmitting the packets on the given P-tunnel to the child until the 774 newer UMH has a chance to start transmitting the packets on the given 775 P-tunnel to the child. However, the control plane operation 776 (modifying the RT of the Leaf A-D route) does not permit the child 777 node to first join the P-tunnel at the new UMH, and then later prune 778 itself from the old UMH; a single control plane operation has both 779 effects. Therefore, to achieve "make before break", timers must be 780 used as follows: 782 1. The old UMH must continue transmitting to the child node for a 783 period of time after it sees the child's Leaf A-D route being 784 withdrawn (or its RT changing to identify a different UMH). 786 2. The child node must continue to accept packets from the old UMH 787 for a period of time before it starts to accept packets from the 788 new UMH (and discard packets from the old). 790 Further, the timer in 1 should be longer than the timer in 2. This 791 allows the child to switch from one UMH to another without any loss 792 of data. 794 10. IANA Considerations 796 This document contains no actions for IANA. 798 11. Acknowledgments 800 The authors wish to thank Yakov Rekhter for his contributions to this 801 work. We also wish to thank Huajin Jeng and Samir Saad for their 802 contributions, and to thank Thomas Morin for pointing out some of the 803 issues that needed further elaboration. 805 Section 6.1 discusses the importance of having an MPLS label 806 allocation policy that, when ingress replication is used, allows an 807 egress PE to infer the identity of a received packet's ingress PE. 808 This issue was first raised in earlier work by Xu Xiaohu. 810 12. Security Considerations 812 No security considerations are raised by this document beyond those 813 already discussed in [RFC6513] and [RFC6514]. 815 13. References 817 13.1. Normative References 819 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 820 Requirement Levels", BCP 14, RFC 2119, March 1997. 822 [RFC6513] Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP 823 VPNs", RFC 6513, February 2012. 825 [RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP 826 Encodings and Procedures for Multicast in MPLS/BGP IP 827 VPNs", RFC 6514, February 2012. 829 [RFC6515] Aggarwal, R. and E. Rosen, "IPv4 and IPv6 Infrastructure 830 Addresses in BGP Updates for Multicast VPN", RFC 6515, 831 February 2012. 833 13.2. Informative References 835 [C-BIDIR-IR] 836 Zhang, Z., Rekhter, Y., and A. Dolganow, "Simulating 837 'Partial Mesh of MP2MP P-Tunnels' with Ingress 838 Replication", internet-draft draft-ietf-bess-mvpn-bidir- 839 ingress-replication-00, January 2015. 841 [MVPN-BIDIR] 842 Rosen, E., Wijnands, IJ., Cai, Y., and A. Boers, ""MVPN: 843 Using Bidirectional P-Tunnels", internet-draft draft-ietf- 844 bess-mvpn-bidir-04, April 2015. 846 [MVPN-XNET] 847 Rekhter, Y., Rosen, E., Aggarwal, R., Cai, Y., and T. 848 Morin, "Extranet Multicast in BGP/IP MPLS VPNs", internet- 849 draft draft-ietf-bess-mvpn-extranet-02, May 2015. 851 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 852 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 853 Tunnels", RFC 3209, December 2001. 855 [RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP 856 Specification", RFC 5036, October 2007. 858 [RFC6388] Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas, 859 "Label Distribution Protocol Extensions for Point-to- 860 Multipoint and Multipoint-to-Multipoint Label Switched 861 Paths", RFC 6388, November 2011. 863 [RFC6625] Rosen, E., Rekhter, Y., Hendrickx, W., and R. Qiu, 864 "Wildcards in Multicast VPN Auto-Discovery Routes", RFC 865 6625, May 2012. 867 [RFC7524] Rekhter, Y., Rosen, E., Aggarwal, R., Morin, T., 868 Grosclaude, I., Leymann, N., and S. Saad, "Inter-Area P2MP 869 Segmented LSPs", RFC 7524, May 2015. 871 Authors' Addresses 873 Eric C. Rosen (editor) 874 Juniper Networks, Inc. 875 10 Technology Park Drive 876 Westford, Massachusetts 01886 877 United States 879 Email: erosen@juniper.net 881 Karthik Subramanian 882 Cisco Systems, Inc. 883 170 Tasman Drive 884 San Jose, California 95134 885 United States 887 Email: kartsubr@cisco.com 889 Zhaohui Zhang 890 Juniper Networks, Inc. 891 10 Technology Park Drive 892 Westford, Massachusetts 01886 893 United States 895 Email: zzhang@juniper.net