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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) == Missing Reference: 'AII-TYPES' is mentioned on line 259, but not defined == Missing Reference: 'DTLS' is mentioned on line 800, but not defined == Missing Reference: 'LPE' is mentioned on line 800, but not defined == Missing Reference: '2547bis' is mentioned on line 1200, but not defined == Missing Reference: 'L2VPN-REQS' is mentioned on line 1196, but not defined == Unused Reference: 'BRADNER' is defined on line 1231, but no explicit reference was found in the text == Unused Reference: 'MP-BGP' is defined on line 1234, but no explicit reference was found in the text == Unused Reference: 'EXT-COMM' is defined on line 1237, but no explicit reference was found in the text == Unused Reference: 'RFC2685' is defined on line 1280, but no explicit reference was found in the text ** Obsolete normative reference: RFC 2858 (ref. 'MP-BGP') (Obsoleted by RFC 4760) ** Obsolete normative reference: RFC 3036 (ref. 'LDP') (Obsoleted by RFC 5036) == Outdated reference: A later version (-09) exists of draft-ietf-l3vpn-bgpvpn-auto-05 == Outdated reference: A later version (-07) exists of draft-ietf-l2tpext-l2vpn-05 == Outdated reference: A later version (-07) exists of draft-ietf-l2vpn-requirements-04 == Outdated reference: A later version (-15) exists of draft-ietf-pwe3-iana-allocation-11 == Outdated reference: A later version (-09) exists of draft-ietf-l2vpn-vpls-ldp-06 == Outdated reference: A later version (-08) exists of draft-ietf-l2vpn-vpls-bgp-05 Summary: 5 errors (**), 0 flaws (~~), 18 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group E. Rosen 3 Internet-Draft W. Luo 4 Expires: February 19, 2006 B. Davie 5 Cisco Systems, Inc. 6 V. Radoaca 7 August 18, 2005 9 Provisioning, Autodiscovery, and Signaling in L2VPNs 10 draft-ietf-l2vpn-signaling-05.txt 12 Status of this Memo 14 By submitting this Internet-Draft, each author represents that any 15 applicable patent or other IPR claims of which he or she is aware 16 have been or will be disclosed, and any of which he or she becomes 17 aware will be disclosed, in accordance with Section 6 of BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on February 19, 2006. 37 Copyright Notice 39 Copyright (C) The Internet Society (2005). 41 Abstract 43 There are a number of different kinds of "Provider Provisioned Layer 44 2 VPNs" (L2VPNs). The different kinds of L2VPN may have different 45 "provisioning models", i.e., different models for what information 46 needs to be configured in what entities. Once configured, the 47 provisioning information is distributed by a "discovery process". 48 When the discovery process is complete, a signaling protocol is 49 automatically invoked. The signaling protocol sets up the mesh of 50 Pseudowires (PWs) that form the (virtual) backbone of the L2VPN. Any 51 PW signaling protocol needs to have a method which allows each PW 52 endpoint to identify the other; thus a PW signaling protocol will 53 have the notion of an endpoint identifier. The semantics of the 54 endpoint identifiers which the signaling protocol uses for a 55 particular type of L2VPN are determined by the provisioning model. 56 This document specifies a number of L2VPN provisioning models, and 57 further specifies the semantic structure of the endpoint identifiers 58 required by each provisioning model. It discusses the way in which 59 the endpoint identifiers are distributed by the discovery process, 60 especially when the discovery process is based upon the Border 61 Gateway Protocol (BGP). It then specifies how the endpoint 62 identifiers are carried in the two signaling protocols that are used 63 to set up PWs, the Label Distribution Protocol (LDP) and the Layer 2 64 Tunneling Protocol (L2TPv3). 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 70 2. Signaling Protocol Framework . . . . . . . . . . . . . . . . . 7 71 2.1. Endpoint Identification . . . . . . . . . . . . . . . . . 7 72 2.2. Creating a Single Bidirectional Pseudowire . . . . . . . . 8 73 2.3. Attachment Identifiers and Forwarders . . . . . . . . . . 9 75 3. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 11 76 3.1. Individual Point-to-Point Pseudowires . . . . . . . . . . 11 77 3.1.1. Provisioning Models . . . . . . . . . . . . . . . . . 11 78 3.1.1.1. Double Sided Provisioning . . . . . . . . . . . . 11 79 3.1.1.2. Single Sided Provisioning with Discovery . . . . . 11 80 3.1.2. Signaling . . . . . . . . . . . . . . . . . . . . . . 12 81 3.2. Virtual Private LAN Service . . . . . . . . . . . . . . . 13 82 3.2.1. Provisioning . . . . . . . . . . . . . . . . . . . . . 13 83 3.2.2. Auto-Discovery . . . . . . . . . . . . . . . . . . . . 14 84 3.2.2.1. BGP-based auto-discovery . . . . . . . . . . . . . 14 85 3.2.3. Signaling . . . . . . . . . . . . . . . . . . . . . . 15 86 3.2.4. Pseudowires as VPLS Attachment Circuits . . . . . . . 16 87 3.3. Colored Pools: Full Mesh of Point-to-Point Pseudowires . . 16 88 3.3.1. Provisioning . . . . . . . . . . . . . . . . . . . . . 16 89 3.3.2. Auto-Discovery . . . . . . . . . . . . . . . . . . . . 17 90 3.3.2.1. BGP-based auto-discovery . . . . . . . . . . . . . 17 91 3.3.3. Signaling . . . . . . . . . . . . . . . . . . . . . . 18 92 3.4. Colored Pools: Partial Mesh . . . . . . . . . . . . . . . 19 93 3.5. Distributed VPLS . . . . . . . . . . . . . . . . . . . . . 20 94 3.5.1. Signaling . . . . . . . . . . . . . . . . . . . . . . 22 95 3.5.2. Provisioning and Discovery . . . . . . . . . . . . . . 23 96 3.5.3. Non-distributed VPLS as a sub-case . . . . . . . . . . 24 97 3.5.4. Splicing and the Data Plane . . . . . . . . . . . . . 24 99 4. Inter-AS Operation . . . . . . . . . . . . . . . . . . . . . . 25 100 4.1. Multihop EBGP redistribution of L2VPN NLRIs . . . . . . . 25 101 4.2. EBGP redistribution of L2VPN NLRIs with Pseudowire 102 Switching . . . . . . . . . . . . . . . . . . . . . . . . 26 103 4.3. Inter-Provider Application of Dist. VPLS Signaling . . . . 27 104 4.4. RT and RD Assignment Considerations . . . . . . . . . . . 28 106 5. Security Considerations . . . . . . . . . . . . . . . . . . . 29 108 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 110 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 31 112 8. Normative References . . . . . . . . . . . . . . . . . . . . . 32 113 9. Informative References . . . . . . . . . . . . . . . . . . . . 33 115 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34 116 Intellectual Property and Copyright Statements . . . . . . . . . . 35 118 1. Introduction 120 [L2VPN-FW] describes a number of different ways in which sets of 121 pseudowires may be combined together into "Provider Provisioned Layer 122 2 VPNs" (L2 PPVPNs, or L2VPNs), resulting in a number of different 123 kinds of L2VPN. Different kinds of L2VPN may have different 124 "provisioning models", i.e., different models for what information 125 needs to be configured in what entities. Once configured, the 126 provisioning information is distributed by a "discovery process", and 127 once the information is discovered, the signaling protocol is 128 automatically invoked to set up the required pseudowires. The 129 semantics of the endpoint identifiers which the signaling protocol 130 uses for a particular type of L2VPN are determined by the 131 provisioning model. That is, different kinds of L2VPN, with 132 different provisioning models, require different kinds of endpoint 133 identifiers. This document specifies a number of PPVPN provisioning 134 models, and specifies the semantic structure of the endpoint 135 identifiers required for each provisioning model. 137 Either LDP (as specified in [LDP] and extended in [PWE3-CONTROL]) or 138 L2TP version 3 (as specified in [L2TP-BASE] and extended in [L2TP- 139 L2VPN]) can be used as signaling protocols to set up and maintain 140 pseudowires (PWs) [PWE3-ARCH]. Any protocol which sets up 141 connections must provide a way for each endpoint of the connection to 142 identify the other; each PW signaling protocol thus provides a way to 143 identify the PW endpoints. Since each signaling protocol needs to 144 support all the different kinds of L2VPN and provisioning models, the 145 signaling protocol must have a very general way of representing 146 endpoint identifiers, and it is necessary to specify rules for 147 encoding each particular kind of endpoint identifier into the 148 relevant fields of each signaling protocol. This document specifies 149 how to encode the endpoint identifiers of each provisioning model 150 into the LDP and L2TPv3 signaling protocols. 152 We make free use of terminology from [L2VPN-FW], [L2VPN-TERM], and 153 [PWE3-ARCH], in particular the terms "Attachment Circuit", 154 "pseudowire", "PE", "CE". 156 Section 2 provides an overview of the relevant aspects of [PWE3- 157 CONTROL] and [L2TP-L2VPN]. 159 Section 3 details various provisioning models and relates them to the 160 signaling process and to the discovery process. The way in which the 161 signaling mechanisms can be integrated with BGP-based auto-discovery 162 is covered in some detail. 164 Section 4 explains how the procedures for discovery and signaling can 165 be applied in a multi-AS environment and outlines several options for 166 the establishment of multi-AS L2VPNs. 168 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 169 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 170 document are to be interpreted as described in RFC 2119 172 2. Signaling Protocol Framework 174 2.1. Endpoint Identification 176 Per [L2VPN-FW], a pseudowire can be thought of as a relationship 177 between a pair of "Forwarders". In simple instances of VPWS, a 178 Forwarder binds a pseudowire to a single Attachment Circuit, such 179 that frames received on the one are sent on the other, and vice 180 versa. In VPLS, a Forwarder binds a set of pseudowires to a set of 181 Attachment Circuits; when a frame is received from any member of that 182 set, a MAC address table is consulted (and various 802.1d procedures 183 executed) to determine the member or members of that set on which the 184 frame is to be transmitted. In more complex scenarios, Forwarders 185 may bind PWs to PWs, thereby "splicing" two PWs together; this is 186 needed, e.g., to support distributed VPLS and some inter-AS 187 scenarios. 189 In simple VPWS, where a Forwarder binds exactly one PW to exactly one 190 Attachment Circuit, a Forwarder can be identified by identifying its 191 Attachment Circuit. In simple VPLS, a Forwarder can be identified by 192 identifying its PE device and its VPN. 194 To set up a PW between a pair of Forwarders, the signaling protocol 195 must allow the Forwarder at one endpoint to identify the Forwarder at 196 the other. In [PWE3-CONTROL], the term "Attachment Identifier", or 197 "AI", is used to refer to a quantity whose purpose is to identify a 198 Forwarder. In [L2TP-L2VPN], the term "Forwarder Identifier" is used 199 for the same purpose. In the context of this document, "Attachment 200 Identifier" and "Forwarder Identifier" are used interchangeably. 202 [PWE3-CONTROL] specifies two FEC elements that can be used when 203 setting up pseudowires, the PWid FEC element, and the Generalized Id 204 FEC element. The PWid FEC element carries only one Forwarder 205 identifier; it can be thus be used only when both forwarders have the 206 same identifier, and when that identifier can be coded as a 32-bit 207 quantity. The Generalized Id FEC element carries two Forwarder 208 identifiers, one for each of the two Forwarders being connected. 209 Each identifier is known as an Attachment Identifier, and a signaling 210 message carries both a "Source Attachment Identifier" (SAI) and a 211 "Target Attachment Identifier" (TAI). 213 The Generalized ID FEC element also provides some additional 214 structuring of the identifiers. It is assumed that the SAI and TAI 215 will sometimes have a common part, called the "Attachment Group 216 Identifier" (AGI), such that the SAI and TAI can each be thought of 217 as the concatenation of the AGI with an "Attachment Individual 218 Identifier" (AII). So the pair of identifiers is encoded into three 219 fields: AGI, Source AII (SAII), and Target AII (TAII). The SAI is 220 the concatenation of the AGI and the SAII, while the TAI is the 221 concatenation of the AGI and the TAII. 223 Similarly, [L2TP-L2VPN] allows using one or two Forwarder Identifiers 224 to set up pseudowires. If only the target Forwarder Identifier is 225 used in L2TP signaling messages, both the source and target 226 Forwarders are assumed to have the same value. If both the source 227 and target Forwarder Identifiers are carried in L2TP signaling 228 messages, each Forwarder uses a locally significant identifier value. 230 The Forwarder Identifier in [L2TP-L2VPN] is an equivalent term as 231 Attachment Identifier in [PWE3-CONTROL]. A Forwarder Identifier also 232 consists of an Attachment Group Identifier and an Attachment 233 Individual Identifier. Unlike the Generalized ID FEC element, the 234 AGI and AII are carried in distinct L2TP Attribute-Value-Pairs 235 (AVPs). The AGI is encoded in the AGI AVP, and the SAII and TAII are 236 encoded in the Local End ID AVP and the Remote End ID AVP 237 respectively. The source Forwarder Identifier is the concatenation 238 of the AGI and SAII, while the target Forwarder Identifier is the 239 concatenation of the AGI and TAII. 241 In applications that group sets of PWs into "Layer 2 Virtual Private 242 Networks", the AGI can be thought of as a "VPN Identifier". 244 It should be noted that while different forwarders support different 245 applications, the type of application (e.g., VPLS vs. VPWS) cannot 246 necessarily be inferred from the forwarders' identifiers. A router 247 receiving a signaling message with a particular TAI will have to be 248 able to determine which of its local forwarders is identified by that 249 TAI, and to determine the application provided by that forwarder. 250 But other nodes may not be able to infer the application simply by 251 inspection of the signaling messages. 253 In this document some further structure of the AGI and AII is 254 proposed for certain L2VPN applications. We note that [PWE3-CONTROL] 255 defines a TLV structure for AGI and AII fields. Thus, an operator 256 who chooses to use the AII structure defined here could also make use 257 of different AGI or AII types if he also wanted to use a different 258 structure for these identifiers for some other application. For 259 example, the long prefix type of [AII-TYPES] could be used to enable 260 the communication of administrative information, perhaps combined 261 with information learned during autodiscovery. 263 2.2. Creating a Single Bidirectional Pseudowire 265 In any form of LDP-based signaling, each PW endpoint must initiate 266 the creation of a unidirectional LSP. A PW is a pair of such LSPs. 267 In most of the PPVPN provisioning models, the two endpoints of a 268 given PW can simultaneously initiate the signaling for it. They must 269 therefore have some way of determining when a given pair of LSPs are 270 intended to be associated together as a single PW. 272 The way in which this association is done is different for the 273 various different L2VPN services and provisioning models. The 274 details appear in later sections. 276 L2TP signaling inherently establishes a bidirectional session that 277 carries a PW between two PW endpoints. The two endpoints can also 278 simultaneously initiate the signaling for a given PW. It is possible 279 that two PWs can be established for a pair of Forwarders. 281 In order to avoid setting up duplicated pseudowires between two 282 Forwarders, each PE must be able to independently detect such a 283 pseudowire tie. The procedures of detecting a pseudowire tie is 284 described in [L2TP-L2VPN] 286 2.3. Attachment Identifiers and Forwarders 288 Every Forwarder in a PE must be associated with an Attachment 289 Identifier (AI), either through configuration or through some 290 algorithm. The Attachment Identifier must be unique in the context 291 of the PE router in which the Forwarder resides. The combination must be globally unique. 294 As specified in [PWE3-CONTROL], the Attachment Identifier may consist 295 of an Attachment Group Identifier (AGI) plus an Attachment Individual 296 Identifier (AII). In the context of this document, an AGI may be 297 thought of as a VPN-id, or a VLAN identifier, some attribute which is 298 shared by all the Attachment Circuits which are allowed to be 299 connected. 301 It is sometimes helpful to consider a set of attachment circuits at a 302 single PE to belong to a common "pool". For example a set of 303 attachment circuits that connect a single CE to a given PE may be 304 considered a pool. The use of pools is described in detail in 305 Section 3.3. 307 The details for how to construct the AGI and AII fields identifying 308 the pseudowire endpoints in particular provisioning models are 309 discussed later in this paper. 311 We can now consider an LSP for one direction of a pseudowire to be 312 identified by: 314 o , PE2, > 316 and the LSP in the opposite direction of the pseudowire will be 317 identified by: 319 o , PE1, > 321 A pseudowire is a pair of such LSPs. In the case of using L2TP 322 signaling, these refer to the two directions of an L2TP session. 324 When a signaling message is sent from PE1 to PE2, and PE1 needs to 325 refer to an Attachment Identifier which has been configured on one of 326 its own Attachment Circuits (or pools), the Attachment Identifier is 327 called a "Source Attachment Identifier". If PE1 needs to refer to an 328 Attachment Identifier which has been configured on one of PE2's 329 Attachment Circuits (or pools), the Attachment Identifier is called a 330 "Target Attachment Identifier". (So an SAI at one endpoint is a TAI 331 at the remote endpoint, and vice versa.) 333 In the signaling protocol, we define encodings for the following 334 three fields: 336 o Attachment Group Identifier (AGI) 338 o Source Attachment Individual Identifier (SAII) 340 o Target Attachment Individual Identifier (TAII) 342 If the AGI is non-null, then the SAI consists of the AGI together 343 with the SAII, and the TAI consists of the TAII together with the 344 AGI. If the AGI is null, then the SAII and TAII are the SAI and TAI 345 respectively. 347 The intention is that the PE which receives an LDP Label Mapping 348 message or an L2TP Incoming Call Request (ICRQ) message containing a 349 TAI will be able to map that TAI uniquely to one of its Attachment 350 Circuits (or pools). The way in which a PE maps a TAI to an 351 Attachment Circuit (or pool) should be a local matter (including the 352 choice of whether to use some or all of the bytes in the TAI for the 353 mapping). So as far as the signaling procedures are concerned, the 354 TAI is really just an arbitrary string of bytes, a "cookie". 356 3. Applications 358 In this section, we specify the way in which the pseudowire signaling 359 using the notion of source and target Forwarder is applied for a 360 number of different applications. For some of the applications, we 361 specify the way in which different provisioning models can be used. 362 However, this is not meant to be an exhaustive list of the 363 applications, or an exhaustive list of the provisioning models that 364 can be applied to each application. 366 3.1. Individual Point-to-Point Pseudowires 368 The signaling specified in this document can be used to set up 369 individually provisioned point-to-point pseudowires. In this 370 application, each Forwarder binds a single PW to a single Attachment 371 Circuit. Each PE must be provisioned with the necessary set of 372 Attachment Circuits, and then certain parameters must be provisioned 373 for each Attachment Circuit. 375 3.1.1. Provisioning Models 377 3.1.1.1. Double Sided Provisioning 379 In this model, the Attachment Circuit must be provisioned with a 380 local name, a remote PE address, and a remote name. During 381 signaling, the local name is sent as the SAII, the remote name as the 382 TAII, and the AGI is null. If two Attachment Circuits are to be 383 connected by a PW, the local name of each must be the remote name of 384 the other. 386 Note that if the local name and the remote name are the same, the 387 PWid FEC element can be used instead of the Generalized ID FEC 388 element in the LDP based signaling. 390 With L2TP signaling, the local name is sent in Local End ID AVP, the 391 remote name in Remote End ID AVP. The AGI AVP is optional. If 392 present, it contains a zero-length AGI value. If the local name and 393 the remote name are the same, Local End ID AVP can be omitted from 394 L2TP signaling messages. 396 3.1.1.2. Single Sided Provisioning with Discovery 398 In this model, each Attachment Circuit must be provisioned with a 399 local name. The local name consists of a VPN-id (signaled as the 400 AGI) and an Attachment Individual Identifier which is unique relative 401 to the AGI. If two Attachment circuits are to be connected by a PW, 402 only one of them needs to be provisioned with a remote name (which of 403 course is the local name of the other Attachment Circuit). Neither 404 needs to be provisioned with the address of the remote PE, but both 405 must have the same VPN-id. 407 As part of an auto-discovery procedure, each PE advertises its 408 pairs. Each PE compares its local pairs with the pairs advertised by 410 the other PEs. If PE1 has a local pair with 411 value , and PE2 has a local pair with 412 value , PE1 will thus be able to discover that it needs to 413 connect to PE2. When signaling, it will use "fred" as the TAII, and 414 will use V as the AGI. PE1's local name for the Attachment Circuit 415 is sent as the SAII. 417 The primary benefit of this provisioning model when compared to 418 Double Sided Provisioning is that it enables one to move an 419 Attachment Circuit from one PE to another without having to 420 reconfigure the remote endpoint. However, compared to the approach 421 described in Section 3.3 below, it imposes a greater burden on the 422 discovery mechanism, because each attachment circuit's name must be 423 advertised individually (i.e. there is no aggregation of AC names in 424 this simple scheme). 426 3.1.2. Signaling 428 The LDP-based signaling follows the procedures specified in [PWE3- 429 CONTROL]. That is, one PE (PE1) sends a Label Mapping Message to 430 another PE (PE2) to establish an LSP in one direction. If that 431 message is processed successfully, and there is not yet an LSP for 432 the pseudowire in the opposite (PE1->PE2) direction, then PE2 sends a 433 Label Mapping Message to PE1. 435 In addition to the procedures of [PWE3-CONTROL], when a PE receives a 436 Label Mapping Message, and the TAI identifies a particular Attachment 437 Circuit which is configured to be bound to a point-to-point PW, then 438 the following checks must be made. 440 If the Attachment Circuit is already bound to a pseudowire (including 441 the case where only one of the two LSPs currently exists), and the 442 remote endpoint is not PE1, then PE2 sends a Label Release message to 443 PE1, with a Status Code meaning "Attachment Circuit bound to 444 different PE", and the processing of the Mapping message is complete. 446 If the Attachment Circuit is already bound to a pseudowire (including 447 the case where only one of the two LSPs currently exists), but the AI 448 at PE1 is different than that specified in the AGI/SAII fields of the 449 Mapping message then PE2 sends a Label Release message to PE1, with a 450 Status Code meaning "Attachment Circuit bound to different remote 451 Attachment Circuit", and the processing of the Mapping message is 452 complete. 454 Similarly with the L2TP-based signaling, when a PE receives an ICRQ 455 message, and the TAI identifies a particular Attachment Circuit which 456 is configured to be bound to a point-to-point PW, it performs the 457 following checks. 459 If the Attachment Circuit is already bound to a pseudowire, and the 460 remote endpoint is not PE1, then PE2 sends a Call Disconnect Notify 461 (CDN) message to PE1, with a Status Code meaning "Attachment Circuit 462 bound to different PE", and the processing of the ICRQ message is 463 complete. 465 If the Attachment Circuit is already bound to a pseudowire, but the 466 pseudowire is bound to a Forwarder on PE1 with the AI different than 467 that specified in the SAI fields of the ICRQ message, then PE2 sends 468 a CDN message to PE1, with a Status Code meaning "Attachment Circuit 469 bound to different remote Attachment Circuit", and the processing of 470 the ICRQ message is complete. 472 These errors could occur as the result of misconfigurations. 474 3.2. Virtual Private LAN Service 476 In the VPLS application [L2VPN-REQ, VPLS], the Attachment Circuits 477 can be though of as LAN interfaces which attach to "virtual LAN 478 switches", or, in the terminology of [L2VPN-FW], "Virtual Switching 479 Instances" (VSIs). Each Forwarder is a VSI that attaches to a number 480 of PWs and a number of Attachment Circuits. The VPLS service [L2VPN- 481 REQ, VPLS] requires that a single pseudowire be created between each 482 pair of VSIs that are in the same VPLS. Each PE device may have a 483 multiple VSIs, where each VSI belongs to a different VPLS. 485 3.2.1. Provisioning 487 Each VPLS must have a globally unique identifier, which we call a 488 VPN-id. Every VSI must be configured with the VPN-id of the VPLS to 489 which it belongs. 491 Each VSI must also have a unique identifier, which we call a VSI-ID. 492 This can be formed automatically by concatenating its VPN-id with an 493 IP address of its PE router. (Note that the PE address here is used 494 only as a form of unique identifier; a service provider could choose 495 to use some other numbering scheme if that was desired. See 496 Section 4 for a discussion of VSI-ID assignment in the case of 497 multiple providers.) 499 3.2.2. Auto-Discovery 501 3.2.2.1. BGP-based auto-discovery 503 The framework for BGP-based auto-discovery for a generic L2VPN 504 service is as described in [BGP-AUTO], section 3.2. 506 The AFI/SAFI used would be: 508 o An AFI specified by IANA for L2VPN. (This is the same for all 509 L2VPN schemes.) 511 o A SAFI specified by IANA specifically for an L2VPN service whose 512 pseudowires are set up using the procedures described in the 513 current document. 515 See Section 6 for further discussion of AFI/SAFI assignment. 517 In order to use BGP-based auto-discovery as specified in [BGP-AUTO], 518 the globally unique identifier associated with a VPLS must be 519 encodable as an 8-byte Route Distinguisher (RD). If the globally 520 unique identifier for a VPLS is an RFC2685 VPN-id, it can be encoded 521 as an RD as specified in [BGP-AUTO]. However, any other method of 522 assigning a unique identifier to a VPLS and encoding it as an RD 523 (using the encoding techniques of [RFC2547bis]) will do. 525 Each VSI needs to have a unique identifier, which can be encoded as a 526 BGP NLRI. This is formed by prepending the RD (from the previous 527 paragraph) to an IP address of the PE containing the VSI. Note that 528 the role of this address is simply as a readily available unique 529 identifier for the VSIs within a VPN; it does not need to be globally 530 routable. An alternate numbering scheme (e.g. numbering the VSIs of 531 a single VPN from 1 to n) could be used if desired. 533 (Note also that it is not strictly necessary for all the VSIs in the 534 same VPLS to have the same RD, all that is really necessary is that 535 the NLRI uniquely identify a VSI.) 537 Each VSI needs to be associated with one or more Route Target (RT) 538 Extended Communities, as discussed in [BGP-AUTO]. These control the 539 distribution of the NLRI, and hence will control the formation of the 540 overlay topology of pseudowires that constitutes a particular VPLS. 542 Auto-discovery proceeds by having each PE distribute, via BGP, the 543 NLRI for each of its VSIs, with itself as the BGP next hop, and with 544 the appropriate RT for each such NLRI. Typically, each PE would be a 545 client of a small set of BGP route reflectors, which would 546 redistribute this information to the other clients. 548 If a PE has a VSI with a particular RT, it can then import all the 549 NLRI which have that same RT, and from the BGP next hop attribute of 550 these NLRI it will learn the IP addresses of the other PE routers 551 which have VSIs with the same RT. The considerations of [RFC2547bis] 552 section 4.3.3 on the use of route reflectors apply. 554 If a particular VPLS is meant to be a single fully connected LAN, all 555 its VSIs will have the same RT, in which case the RT could be (though 556 it need not be) an encoding of the VPN-id. If a particular VPLS 557 consists of multiple VLANs, each VLAN must have its own unique RT. A 558 VSI can be placed in multiple VLANS (or even in multiple VPLSes) by 559 assigning it multiple RTs. 561 Note that hierarchical VPLS can be set up by assigning multiple RTs 562 to some of the VSIs; the RT mechanism allows one to have complete 563 control over the pseudowire overlay which constitutes the VPLS 564 topology. 566 If Distributed VPLS (described in Section 3.5) is deployed, only the 567 N-PEs participate in BGP-based autodiscovery. This means that an 568 N-PE would need to advertise reachability to each of the VSIs that it 569 supports, including those located in U-PEs to which it is connected. 570 To create a unique identifier for each such VSI, an IP address of 571 each U-PE combined with the RD for the VPLS instance could be used. 573 In summary, the BGP advertisement for a particular VSI at a given PE 574 will contain: 576 o an NLRI of AFI = L2VPN, SAFI = TBD, encoded as RD:PE_addr 578 o a BGP next hop equal to the loopback address of the PE 580 o an extended community attribute containing one or more RTs. 582 Note that this advertisement is quite similar to the NLRI format 583 defined in [BGP-VPLS], the main difference being that [BGP-VPLS] also 584 includes a label block in the NLRI. Interoperability between the 585 VPLS scheme defined here and that defined in [BGP-VPLS] is beyond the 586 scope of this document. 588 3.2.3. Signaling 590 It is necessary to create Attachment Identifiers which identify the 591 VSIs. In the preceding section, a VSI-ID was encoded as RD:PE_addr 592 for the purposes of autodiscovery. For signaling purposes, the same 593 information is carried but is encoded slightly differently. Noting 594 that the RD is effectively a VPN identifier, we therefore encode the 595 RD in the AGI field, and place the PE_addr (or, more generally, the 596 VSI-ID that was advertised in BGP, minus the RD) in the TAII field. 597 The combination of AGI and TAII is sufficient to fully specify the 598 VSI to which this pseudowire is to be connected, in both single AS 599 and inter-AS environments. The SAII SHOULD be null. 601 The structure of the AGI and AII fields for the Generalized ID FEC in 602 LDP is defined in [PWE3-CONTROL]. The AGI field in this case 603 consists of a Type of 1, a length field of value 8, and the 8 bytes 604 of the RD. The TAII consists of a Type of 1, a length field of value 605 4, followed by the 4-byte PE address (or other 4-byte identifier). 606 See Section 6 for discussion of the AGI and AII Type assignment. 608 The encoding of the AGI and AII in L2TP is specified in [L2TP-L2VPN]. 610 Note that it is not possible using this technique to set up more than 611 one PW per pair of VSIs. 613 3.2.4. Pseudowires as VPLS Attachment Circuits 615 It is also possible using this technique to set up a PW which 616 attaches at one endpoint to a VSI, but at the other endpoint only to 617 an Attachment Circuit. However, in this case there may be more than 618 one PW terminating on a given VSI, which must somehow be 619 distinguished, so that the SAIIs cannot be null in this case. 620 Rather, each such PW must have an SAII which is unique relative to 621 the VSI-ID. 623 3.3. Colored Pools: Full Mesh of Point-to-Point Pseudowires 625 The "Colored Pools" model of operation provides an automated way to 626 deliver Virtual Private Wire Service (VPWS). In this model, each PE 627 may contain several pools of Attachment Circuits, each pool 628 associated with a particular VPN. A PE may contain multiple pools 629 per VPN, as each pool may correspond to a particular CE device. It 630 may be desired to create one pseudowire between each pair of pools 631 that are in the same VPN; the result would be to create a full mesh 632 of CE-CE VCs for each VPN. 634 3.3.1. Provisioning 636 Each pool is configured, and associated with: 638 o a set of Attachment Circuits; 640 o a "color", which can be thought of as a VPN-id of some sort; 642 o a relative pool identifier, which is unique relative to the color. 644 [Note: depending on the technology used for Attachment Circuits, it 645 may or may not be necessary to provision these circuits as well. For 646 example, if the ACs are frame relay circuits, there may be some 647 separate provisioning system to set up such circuits. Alternatively, 648 "provisioning" an AC may be as simple as allocating an unused VLAN ID 649 on an interface, and communicating the choice to the customer. These 650 issues are independent of the procedures described in this document.] 652 The pool identifier, and color, taken together, constitute a globally 653 unique identifier for the pool. Thus if there are n pools of a given 654 color, their pool identifiers can be (though they do not need to be) 655 the numbers 1-n. 657 The semantics are that a pseudowire will be created between every 658 pair of pools that have the same color, where each such pseudowire 659 will be bound to one Attachment Circuit from each of the two pools. 661 If each pool is a set of Attachment Circuits leading to a single CE 662 device, then the layer 2 connectivity among the CEs is controlled by 663 the way the colors are assigned to the pools. To create a full mesh, 664 the "color" would just be a VPN-id. 666 Optionally, a particular Attachment Circuit may be configured with 667 the relative pool identifier of a remote pool. Then that Attachment 668 Circuit would be bound to a particular pseudowire only if that 669 pseudowire's remote endpoint is the pool with that relative pool 670 identifier. With this option, the same pairs of Attachment Circuits 671 will always be bound via pseudowires. 673 3.3.2. Auto-Discovery 675 3.3.2.1. BGP-based auto-discovery 677 The framework for BGP-based auto-discovery for a generic L2VPN 678 service is described in [BGP-AUTO], section 3.2. 680 The AFI/SAFI used would be: 682 o An AFI specified by IANA for L2VPN. (This is the same for all 683 L2VPN schemes.) 685 o A SAFI specified by IANA specifically for an L2VPN service whose 686 pseudowires are set up using the procedures described in the 687 current document. 689 See Section 6 for further discussion of AFI/SAFI assignment. 691 In order to use BGP-based auto-discovery, the color associated with a 692 colored pool must be encodable as both an RT (Route Target) and an RD 693 (Route Distinguisher). The globally unique identifier of a pool must 694 be encodable as NLRI; the color would be encoded as the RD and the 695 pool identifier as a four-byte quantity which is appended to the RD 696 to create the NLRI. 698 Auto-discovery procedures by having each PE distribute, via BGP, the 699 NLRI for each of its pools, with itself as the BGP next hop, and with 700 the RT that encodes the pool's color. If a given PE has a pool with 701 a particular color (RT), it must receive, via BGP, all NLRI with that 702 same color (RT). Typically, each PE would be a client of a small set 703 of BGP route reflectors, which would redistribute this information to 704 the other clients. 706 If a PE has a pool with a particular color, it can then receive all 707 the NLRI which have that same color, and from the BGP next hop 708 attribute of these NLRI will learn the IP addresses of the other PE 709 routers which have pools switches with the same color. It also 710 learns the unique identifier of each such remote pool, as this is 711 encoded in the NLRI. The remote pool's relative identifier can be 712 extracted from the NLRI and used in the signaling, as specified 713 below. 715 In summary, the BGP advertisement for a particular pool of attachment 716 circuits at a given PE will contain: 718 o an NLRI of AFI = L2VPN, SAFI = TBD, encoded as RD:pool_num; 720 o a BGP next hop equal to the loopback address of the PE; 722 o an extended community attribute containing one or more RTs. 724 3.3.3. Signaling 726 The LDP-based signaling follows the procedures specified in [PWE3- 727 CONTROL]. That is, one PE (PE1) sends a Label Mapping Message to 728 another PE (PE2) to establish an LSP in one direction. The address 729 of PE2 is the next-hop address learned via BGP as described above. 730 If the message is processed successfully, and there is not yet an LSP 731 for the pseudowire in the opposite (PE1->PE2) direction, then PE2 732 sends a Label Mapping Message to PE1. Similarly, the L2TPv3-based 733 signaling follows the procedures of [L2TP-BASE]. Additional details 734 on the use of these signaling protocols follow. 736 When a PE sends a Label Mapping message or an ICRQ message to set up 737 a PW between two pools, it encodes the color as the AGI, the local 738 pool's relative identifier as the SAII, and the remote pool's 739 relative identifier as the TAII. 741 The structure of the AGI and AII fields for the Generalized ID FEC in 742 LDP is defined in [PWE3-CONTROL]. The AGI field in this case 743 consists of a Type of 1, a length field of value 8, and the 8 bytes 744 of the RD. The TAII consists of a Type of 1, a length field of value 745 4, followed by the 4-byte remote pool number. The SAII consists of a 746 Type of 1, a length field of value 4, followed by the 4-byte local 747 pool number. See Section 6 for discussion of the AGI and AII Type 748 assignment. Note that the VPLS and VPWS procedures defined in this 749 document can make use of the same AGI Type (1) and the same AII Type 750 (1). 752 The encoding of the AGI and AII in L2TP is specified in [L2TP-L2VPN]. 754 When PE2 receives a Label Mapping message or an ICRQ message from 755 PE1, and the TAI identifies to a pool, and there is already an 756 pseudowire connecting an Attachment Circuit in that pool to an 757 Attachment Circuit at PE1, and the AI at PE1 of that pseudowire is 758 the same as the SAI of the Label Mapping or ICRQ message, then PE2 759 sends a Label Release or CDN message to PE1, with a Status Code 760 meaning "Attachment Circuit already bound to remote Attachment 761 Circuit". This prevents the creation of multiple pseudowires between 762 a given pair of pools. 764 Note that the signaling itself only identifies the remote pool to 765 which the pseudowire is to lead, not the remote Attachment Circuit 766 which is to be bound to the the pseudowire. However, the remote PE 767 may examine the SAII field to determine which Attachment Circuit 768 should be bound to the pseudowire. 770 3.4. Colored Pools: Partial Mesh 772 The procedures for creating a partial mesh of pseudowires among a set 773 of colored pools are substantially the same as those for creating a 774 full mesh, with the following exceptions: 776 o Each pool is optionally configured with a set of "import RTs" and 777 "export RTs"; 779 o During BGP-based auto-discovery, the pool color is still encoded 780 in the RD, but if the pool is configured with a set of "export 781 RTs", these are are encoded in the RTs of the BGP Update messages, 782 INSTEAD of the color; 784 o If a pool has a particular "import RT" value X, it will create a 785 PW to every other pool which has X as one of its "export RTs". 786 The signaling messages and procedures themselves are as in section 787 3.3.3. 789 As a simple example, consider the task of building a hub-and-spoke 790 topology with a single hub. One pool, the "hub" pool, is configured 791 with an export RT of RT_hub and an import RT of RT_spoke. All other 792 pools (the spokes) are configured with an export RT of RT_spoke and 793 an import RT of RT_hub. Thus the Hub pool will connect to the 794 spokes, and vice-versa, but the spoke pools will not connect to each 795 other. More complex examples are presented in section 4.2.2 of [BGP- 796 AUTO]. 798 3.5. Distributed VPLS 800 In Distributed VPLS ([L2VPN-FW], [DTLS], [LPE]), the VPLS 801 functionality of a PE router is divided among two systems: a U-PE and 802 an N-PE. The U-PE sits between the user and the N-PE. VSI 803 functionality (e.g., MAC address learning and bridging) is performed 804 on the U-PE. A number of U-PEs attach to an N-PE. For each VPLS 805 supported by a U-PE, the U-PE maintains a pseudowire to each other 806 U-PE in the same VPLS. However, the U-PEs do not maintain signaling 807 control connections with each other. Rather, each U-PE has only a 808 single signaling connection, to its N-PE. In essence, each U-PE-to- 809 U-PE pseudowire is composed of three pseudowires spliced together: 810 one from U-PE to N-PE, one from N-PE to N-PE, and one from N-PE to 811 U-PE. 813 Consider for example the following topology: 815 U-PE A-----| |----U-PE C 816 | | 817 | | 818 N-PE E--------N-PE F 819 | | 820 | | 821 U-PE B-----| |-----U-PE D 823 where the four U-PEs are in a common VPLS. We now illustrate how PWs 824 get spliced together in the above topology in order to establish the 825 necessary PWs from U-PE A to the other U-PEs. 827 There are three PWs from A to E. Call these A-E/1, A-E/2, and A-E/3. 828 In order to connect A properly to the other U-PEs, there must be two 829 PWs from E to F (call these E-F/1 and E-F/2), one PW from E to B 830 (E-B/1), one from F to C (F-C/1), and one from F to D (F-D/1). 832 The N-PEs must then splice these pseudowires together to get the 833 equivalent of what the non-distributed VPLS signaling mechanism would 834 provide: 836 o PW from A to B: A-E/1 gets spliced to E-B/1. 838 o PW from A to C: A-E/2 gets spliced to E-F/1 gets spliced to F-C/1. 840 o PW from A to D: A-E/3 gets spliced to E-F/2 gets spliced to F-D/1. 842 It doesn't matter which PWs get spliced together, as long as the 843 result is one from A to each of B, C, and D. 845 Similarly, there are additional PWs which must get spliced together 846 to properly interconnect U-PE B with U-PEs C and D, and to 847 interconnect U-PE C with U-PE D. 849 The following figure illustrates the PWs from A to C and from B to D. 850 For clarity of the figure, the other four PWs are not shown. 852 splicing points 853 | | 854 V V 855 A-C PW <-----><-----------><------> 857 U-PE A-----| |----U-PE C 858 | | 859 | | 860 N-PE E--------N-PE F 861 | | 862 | | 863 U-PE B-----| |-----U-PE D 865 B-D PW <-----><-----------><------> 866 ^ ^ 867 | | 868 splicing points 870 One can see that distributed VPLS does not reduce the number of 871 pseudowires per U-PE, but it does reduce the number of control 872 connections per U-PE. Whether this is worthwhile depends, of course, 873 on what the bottleneck is. 875 3.5.1. Signaling 877 The signaling to support Distributed VPLS can be done with the 878 mechanisms described in this paper. However, the procedures for VPLS 879 (section 3.2.3) need some additional machinery to ensure that the 880 appropriate number of PWs are established between the various N-PEs 881 and U-PEs, and among the N-PEs. 883 At a given N-PE, the directly attached U-PEs in a given VPLS can be 884 numbered from 1 to n. This number identifies the U-PE relative to a 885 particular VPN-id and a particular N-PE. (That is, to uniquely 886 identify the U-PE, the N-PE, the VPN-id, and the U-PE number must be 887 known.) 889 As a result of configuration/discovery, each U-PE must be given a 890 list of pairs. Each element in this list tells the 891 U-PE to set up j PWs to the specified IP address. When the U-PE 892 signals to the N-PE, it sets the AGI to the proper-VPN-id, and sets 893 the SAII to the PW number, and sets the TAII to null. 895 In the above example, U-PE A would be told <3, E>, telling it to set 896 up 3 PWs to E. When signaling, A would set the AGI to the proper 897 VPN-id, and would set the SAII to 1, 2, or 3, depending on which of 898 the three PWs it is signaling. 900 As a result of configuration/discovery, each N-PE must be given the 901 following information for each VPLS: 903 o A "Local" list: {}, where each element tells it to 904 set up j PWs to the locally attached U-PE at the specified 905 address. The number of elements in this list will be n, the 906 number of locally attached U-PEs in this VPLS. In the above 907 example, E would be given the local list: {<3, A>, <3, B>}, 908 telling it to set up 3 PWs to A and 3 to B. 910 o A local numbering, relative to the particular VPLS and the 911 particular N-PE, of its U-PEs. In the above example, E could be 912 told that U-PE A is 1, and U-PE B is 2. 914 o A "Remote" list: {}, telling it to set up k PWs, 915 for each U-PE, to the specified IP address. Each of these IP 916 addresses identifies a N-PE, and k specifies the number of U-PEs 917 at that N-PE which are in the VPLS. In the above example, E would 918 be given the remote list: {<2, F>}. Since N-PE E has two U-PEs, 919 this tells it to set up 4 PWs to N-PE F, 2 for each of its E's 920 U-PEs. 922 The signaling of a PW from N-PE to U-PE is based on the local list 923 and the local numbering of U-PEs. When signaling a particular PW 924 from an N-PE to a U-PE, the AGI is set to the proper VPN-id, and SAII 925 is set to null, and the TAII is set to the PW number (relative to 926 that particular VPLS and U-PE). In the above example, when E signals 927 to A, it would set the TAII to be 1, 2, or 3, respectively, for the 928 three PWs it must set up to A. It would similarly signal three PWs to 929 B. 931 The LSP signaled from U-PE to N-PE is associated with an LSP from 932 N-PE to U-PE in the usual manner. A PW between a U-PE and an N-PE is 933 known as a "U-PW". 935 The signaling of the appropriate set of PWs from N-PE to N-PE is 936 based on the remote list. The PWs between the N-PEs can all be 937 considered equivalent. As long as the correct total number of PWs 938 are established, the N-PEs can splice these PWs to appropriate U-PWs. 939 The signaling of the correct number of PWs from N-PE to N-PE is based 940 on the remote list. The remote list specifies the number of PWs to 941 set up, per local U-PE, to a particular remote N-PE. 943 When signaling a particular PW from an N-PE to an N-PE, the AGI is 944 set to the appropriate VPN-id. The TAII identifies the remote N-PE, 945 as in the non-distributed case, i.e. it contains an IP address of the 946 remote N-PE. If there are n such PWs, they are distinguished by the 947 setting of the SAII, which will be a number from 1 to n inclusive. A 948 PW between two N-PEs is known as an "N-PW". 950 Each U-PW must be "spliced" to an N-PW. This is based on the remote 951 list. If the remote list contains an element , then i U-PWs 952 from each local U-PE must be spliced to i N-PWs from the remote N-PE 953 F. It does not matter which U-PWs are spliced to which N-PWs, as long 954 as this constraint is met. 956 If an N-PE has more than one local U-PE for a given VPLS, it must 957 also ensure that a U-PW from each such U-PE is spliced to a U-PW from 958 each of the other U-PEs. 960 3.5.2. Provisioning and Discovery 962 Every N-PE must be provisioned with the set of VPLS instances it 963 supports, a VPN-id for each one, and a list of local U-PEs for each 964 such VPLS. As part of the discovery procedure, the N-PE advertises 965 the number of U-PEs for each VPLS. See Section 3.2.2 for details. 967 Auto-discovery (e.g., BGP-based) can be used to discover all the 968 other N-PEs in the VPLS, and for each, the number of U-PEs local to 969 that N-PE. From this, one can compute the total number of U-PEs in 970 the VPLS. This information is sufficient to enable one to compute 971 the local list and the remote list for each N-PE. 973 3.5.3. Non-distributed VPLS as a sub-case 975 A PE which is providing "non-distributed VPLS" (i.e., a PE which 976 performs both the U-PE and N-PE functions) can interoperate with 977 N-PE/U-PE pairs that are providing distributed VPLS. The "non- 978 distributed PE" simply advertises, in the discovery procedure, that 979 it has one local U-PE per VPLS. And of course, the non-distributed 980 PE does no splicing. 982 If every PE in a VPLS is providing non-distributed VPLS, and thus 983 every PE advertises itself as an N-PE with one local U-PE, the 984 resultant signaling is exactly the same as that specified in 985 Section 3.2.3 above, except that an SAII value of 1 is used instead 986 of null. (A PE providing non-distributed VPLS should therefore treat 987 SAII values of 1 the same as it treats SAII values of null.) 989 3.5.4. Splicing and the Data Plane 991 Splicing two PWs together is quite straightforward in the MPLS data 992 plane, as moving a packet from one PW directly to another is just a 993 label replace operation on the PW label. When a PW consists of two 994 or more PWs spliced together, it is assumed that the data will go to 995 the node where the splicing is being done, i.e., that the data path 996 will pass through the nodes that participate in PW signaling. 998 Further details on splicing are discussed in [PW-SWITCH]. 1000 4. Inter-AS Operation 1002 The provisioning, autodiscovery and signaling mechanisms described 1003 above can all be applied in an inter-AS environment. As in [2547bis] 1004 there are a number of options for inter-AS operation. 1006 4.1. Multihop EBGP redistribution of L2VPN NLRIs 1008 This option is most like option (c) in [2547bis]. That is, we use 1009 multihop EBGP redistribution of L2VPN NLRIs between source and 1010 destination ASes, with EBGP redistribution of labeled IPv4 routes 1011 from AS to neighboring AS. 1013 An ASBR must maintain labeled IPv4 /32 routes to the PE routers 1014 within its AS. It uses EBGP to distribute these routes to other 1015 ASes, and sets itself as the BGP next hop for these routes. ASBRs in 1016 any transit ASes will also have to use EBGP to pass along the labeled 1017 /32 routes. This results in the creation of a set of label switched 1018 paths from all ingress PE routers to all egress PE routers. Now PE 1019 routers in different ASes can establish multi-hop EBGP connections to 1020 each other, and can exchange L2VPN NLRIs over those connections. 1021 Following such exchanges a pair of PEs in different ASes could 1022 establish an LDP session to signal PWs between each other. 1024 For VPLS, the BGP advertisement and PW signaling are exactly as 1025 described in Section 3.2. As a result of the multihop EBGP session 1026 that exists between source and destination AS, the PEs in one AS that 1027 have VSIs of a certain VPLS will discover the PEs in another AS that 1028 have VSIs of the same VPLS. These PEs will then be able to establish 1029 the appropriate PW signaling protocol session and establish the full 1030 mesh of VSI-VSI pseudowires to build the VPLS as described in Section 1031 3.2.3. 1033 For VPWS, the BGP advertisement and PW signaling are exactly as 1034 described in Section 3.3. As a result of the multihop EBGP session 1035 that exists between source and destination AS, the PEs in one AS that 1036 have pools of a certain color (VPN) will discover PEs in another AS 1037 that have pools of the same color. These PEs will then be able to 1038 establish the appropriate PW signaling protocol session and establish 1039 the full mesh of pseudowires as described in Section 3.2.3. A 1040 partial mesh can similarly be established using the procedures of 1041 Section 3.4. 1043 As in layer 3 VPNs, building an L2VPN that spans the networks of more 1044 than one provider requires some co-ordination in the use of RTs and 1045 RDs. This subject is discussed in more detail in Section 4.4. 1047 4.2. EBGP redistribution of L2VPN NLRIs with Pseudowire Switching 1049 A possible drawback of the approach of the previous section is that 1050 it creates PW signaling sessions among all the PEs of a given L2VPN 1051 (VPLS or VPWS). This means a potentially large number of LDP or 1052 L2TPv3 sessions will cross the AS boundary and that these session 1053 connect to many devices within an AS. In the case were the ASes 1054 belong to different providers, one might imagine that providers would 1055 like to have fewer signaling sessions crossing the AS boundary and 1056 that the entities that terminate the sessions could be restricted to 1057 a smaller set of devices. Furthermore, by forcing the LDP or L2TPv3 1058 signaling sessions to terminate on a small set of ASBRs, a provider 1059 could use standard authentication procedures on a small set of inter- 1060 provider sessions. These concerns motivate the approach described 1061 here. 1063 [PW-SWITCH] describes an approach to "switching" packets from one 1064 pseudowire to another at a particular node. This approach allows an 1065 end-to-end pseudowire to be constructed out of several pseudowire 1066 segments, without maintaining an end-to-end control connection. We 1067 can use this approach to produce an inter-AS solution that more 1068 closely resembles option (b) in [2547bis]. 1070 In this model, we use EBGP redistribution of L2VPN NLRI from AS to 1071 neighboring AS. First, the PE routers use IBGP to redistribute L2VPN 1072 NLRI either to an Autonomous System Border Router (ASBR), or to a 1073 route reflector of which an ASBR is a client. The ASBR then uses 1074 EBGP to redistribute those L2VPN NLRI to an ASBR in another AS, which 1075 in turn distributes them to the PE routers in that AS, or perhaps to 1076 another ASBR which in turn distributes them, and so on. 1078 In this case, a PE can learn the address of an ASBR through which it 1079 could reach another PE to which it wishes to establish a PW. That 1080 is, a local PE will receive a BGP advertisement containing L2VPN NLRI 1081 corresponding to an L2VPN instance in which the local PE has some 1082 attached members. The BGP next-hop for that L2VPN NLRI will be an 1083 ASBR of the local AS. Then, rather than building a control 1084 connection all the way to the remote PE, it builds one only to the 1085 ASBR. A pseudowire segment can now be established from the PE to the 1086 ASBR. The ASBR in turn can establish a PW to the ASBR of the next 1087 AS, and splice that PW to the PW from the PE as described in 1088 Section 3.5.4 and [PW-SWITCH]. Repeating the process at each ASBR 1089 leads to a sequence of PW segments that, when spliced together, 1090 connect the two PEs. 1092 Note that in the approach just described, the local PE may never 1093 learn the IP address of the remote PE. It learns the L2VPN NLRI 1094 advertised by the remote PE, which need not contain the remote PE 1095 address, and it learns the IP address of the ASBR that is the BGP 1096 next hop for that NLRI. 1098 When this approach is used for VPLS, or for full-mesh VPWS, it leads 1099 to a full mesh of pseudowires among the PEs, just as in the previous 1100 section, but it does not require a full mesh of control connections 1101 (LDP or L2TPv3 sessions). Instead the control connections within a 1102 single AS run among all the PEs of that AS and the ASBRs of the AS. 1103 A single control connection between the ASBRs of adjacent ASes can be 1104 used to support however many AS-to-AS pseudowire segments are needed. 1106 Note that the procedures described here will result in the splicing 1107 points being co-located with the ASBRs. It is of course possible to 1108 have multiple ASBR-ASBR connections between a given pair of ASes. In 1109 this case a given PE could choose among the available ASBRs based on 1110 a range of criteria, such as IGP metric, local configuration, etc., 1111 analogous to choosing an exit point in normal IP routing. The use of 1112 multiple ASBRs would lead to greater resiliency (at the timescale of 1113 BGP routing convergence) since a PE could select a new ASBR in the 1114 event of the failure of the one currently in use. 1116 As in layer 3 VPNs, building an L2VPN that spans the networks of more 1117 than one provider requires some co-ordination in the use of RTs and 1118 RDs. This subject is discussed in more detail in Section 4.4. 1120 4.3. Inter-Provider Application of Dist. VPLS Signaling 1122 An alternative approach to inter-provider VPLS can be derived from 1123 the Distributed VPLS approach described above. Consider the 1124 following topology: 1126 PE A --- Network 1 ----- Border ----- Border ----- Network 2 --- PE B 1127 Router 12 Router 21 | 1128 | 1129 PE C 1131 where A, B, and C are PEs in a common VPLS, but Networks 1 and 2 are 1132 networks of different Service Providers. Border Router 12 is Network 1133 1's border router to network 2, and Border Router 21 is Network 2's 1134 border router to Network 1. We suppose further that the PEs are not 1135 "distributed", i.e, that each provides both the U-PE and N-PE 1136 functions. 1138 In this topology, one needs two inter-provider pseudowires: A-B and 1139 A-C. 1141 Suppose a Service Provider decides, for whatever reason, that it does 1142 not want each of its PEs to have a control connection to any PEs in 1143 the other network. Rather, it wants the inter-provider control 1144 connections to run only between the two border routers. 1146 This can be achieved using the techniques of section 3.5, where the 1147 PEs behave like U-PEs, and the BRs behave like N-PEs. In the example 1148 topology, PE A would behave like a U-PE which is locally attached to 1149 BR12; PEs B and C would be have like U-PEs which are locally attached 1150 to BR21; and the two BRs would behave like N-PEs. 1152 As a result, the PW from A to B would consist of three segments: 1153 A-BR12, BR12-BR21, and BR21-B. The border routers would have to 1154 splice the corresponding segments together. 1156 This requires the PEs within a VPLS to be numbered from 1-n (relative 1157 to that VPLS) within a given network. 1159 4.4. RT and RD Assignment Considerations 1161 We note that, in order for any of the inter-AS procedures described 1162 above to work correctly, the two ASes must use RTs and RDs 1163 consistently, just as in layer 3 VPNs [RFC2547bis]. The structure of 1164 RTs and RDs is such that there is not a great risk of accidental 1165 collisions. The main challenge is that it is necessary for the 1166 operator of one AS to know what RT or RTs have been chosen in another 1167 AS for any VPN that has sites in both ASes. As in layer 3 VPNs, 1168 there are many ways to make this work, but all require some co- 1169 operation among the providers. For example, provider A may tag all 1170 the NLRI for a given VPN with a single RT, say RT_A, and provider B 1171 can then configure the PEs that connect to sites of that VPN to 1172 import NLRI that contains that RT. Provider B can choose a different 1173 RT, RT_B, tag all NLRI for this VPN with that RT, and then provider A 1174 can import NLRI with that RT at the appropriate PEs. However this 1175 does require both providers to communicate their choice of RTs for 1176 each VPN. Alternatively both providers could agree to use a common 1177 RT for a given VPN. In any case communication of RTs between the 1178 providers is essential. As in layer 3 VPNs, providers may configure 1179 RT filtering to ensure that only coordinated RT values are allowed 1180 across the AS boundary. 1182 5. Security Considerations 1184 This document describes a number of different L2VPN provisioning 1185 models, and specifies the endpoint identifiers that are required to 1186 support each of the provisioning models. It also specifies how those 1187 endpoint identifiers are mapped into fields of auto-discovery 1188 protocols and signaling protocols. 1190 The security considerations related to the signaling and auto- 1191 discovery protocols are discussed in the relevant protocol 1192 specifications ([BGP-AUTO], [L2TP-BASE], [L2TP-L2VPN], [LDP], [PWE3- 1193 CONTROL]). 1195 The security considerations related to the particular kind of L2VPN 1196 service being supported are discussed in [L2VPN-REQS], [L2VPN-FW], 1197 and [VPLS]. 1199 The security consideration of inter-AS operation are similar to those 1200 for inter-AS L3VPNs [2547bis]. 1202 The way in which endpoint identifiers are mapped into protocol fields 1203 does not create any additional security issues. 1205 6. IANA Considerations 1207 This document requires the assignment of an AFI and a SAFI for L2VPN 1208 NLRI. Both AFI and SAFI may be the same as the values assigned for 1209 [BGP-VPLS]. 1211 [PWE3-IANA] defines registries for AGI types and AII types. This 1212 document defines a specific format for the AGI and the AII, and 1213 proposes the assignment of one value in each registry. The value 1 1214 is assigned in each case, representing the first available value in 1215 the IETF Consensus Range. 1217 7. Acknowledgments 1219 Thanks to Dan Tappan, Ted Qian, Ali Sajassi, Skip Booth, Luca 1220 Martini, Dave McDysan and Francois LeFaucheur for their comments, 1221 criticisms, and helpful suggestions. 1223 Thanks to Tissa Senevirathne, Hamid Ould-Brahim and Yakov Rekhter for 1224 discussing the auto-discovery issues. 1226 Thanks to Vach Kompella for a continuing discussion of the proper 1227 semantics of the generalized identifiers. 1229 8. Normative References 1231 [BRADNER] Bradner, S., "Key words for use in RFCs to Indicate 1232 Requirement Levels", BCP 14, RFC 2119, March 1997. 1234 [MP-BGP] Bates, T., Rekhter, Y., Chandra, R. and D. Katz, 1235 "Multiprotocol Extensions for BGP-4", RFC 2858, June 2000. 1237 [EXT-COMM] Sangli, S., Tappan, D. and Y. Rekhter, "BGP Extended 1238 Communities Attribute", Internet-Draft 1239 draft-ietf-idr-bgp-ext-communities-09, July 2005. 1241 [L2TP-BASE] Lau et. al., "Layer Two Tunneling Protocol (Version 3)", 1242 RFC 3931, March 2005. 1244 [LDP] Anderson et al., "LDP Specification", RFC 3036, Jan 2001. 1246 [PWE3-CONTROL] "Pseudowire Setup and Maintenance using LDP", Martini, 1247 et. al., draft-ietf-pwe3-control-protocol-17.txt, June 2005. 1249 9. Informative References 1251 [BGP-AUTO] "Using BGP as an Auto-Discovery Mechanism for Network- 1252 based VPNs", Ould-Brahim et. al., 1253 draft-ietf-l3vpn-bgpvpn-auto-05.txt, February 2005 1255 [L2TP-L2VPN] "L2VPN Extensions for L2TP", Luo, 1256 draft-ietf-l2tpext-l2vpn-05.txt, June 2005 1258 [L2VPN-FW] "L2VPN Framework", Andersson et. al., 1259 draft-ietf-l2vpn-l2-framework-05.txt, June 2004 1261 [L2VPN-REQ] "Service Requirements for Layer 2 Provider Provisioned 1262 Virtual Private Network Services", Augustyn, Serbest, et. al., 1263 draft-ietf-l2vpn-requirements-04.txt, February 2005 1265 [L2VPN-TERM] Andersson, Madsen, "PPVPN Terminology", RFC 4026, March 1266 2005. 1268 [PWE3-ARCH] Bryant, Pate, et. al., "PWE3 Architecture", RFC 3985, 1269 March 2005. 1271 [PW-SWITCH] "Pseudo Wire Switching", Martini, et. al., 1272 draft-martini-pwe3-pw-switching-03.txt, April 2005 1274 [PWE3-IANA] "IANA Allocations for pseudo Wire Edge to Edge Emulation 1275 (PWE3)", Martini, draft-ietf-pwe3-iana-allocation-11.txt, June 2005 1277 [RFC2547bis], "BGP/MPLS IP VPNs", Rosen, Rekhter, et. al., 1278 draft-ietf-l3vpn-rfc2547bis-03.txt, October 2004 1280 [RFC2685] "Virtual Private Networks Identifier", Fox, Gleeson, 1281 September 1999 1283 [VPLS] "Virtual Private LAN Services over MPLS", Laserre, et. al., 1284 draft-ietf-l2vpn-vpls-ldp-06.txt, February 2005 1286 [BGP-VPLS] "Virtual Private LAN Service", Kompella et al., 1287 draft-ietf-l2vpn-vpls-bgp-05.txt, April 2005 1289 Authors' Addresses 1291 Eric Rosen 1292 Cisco Systems, Inc. 1293 1414 Mass. Ave. 1294 Boxborough, MA 01719 1295 USA 1297 Email: erosen@cisco.com 1299 Wei Luo 1300 Cisco Systems, Inc. 1301 170 W Tasman Dr. 1302 San Jose, CA 95134 1303 USA 1305 Email: luo@cisco.com 1307 Bruce Davie 1308 Cisco Systems, Inc. 1309 1414 Mass. Ave. 1310 Boxborough, MA 01719 1311 USA 1313 Email: bsd@cisco.com 1315 Vasile Radoaca 1317 Email: radoaca@hotmail.com 1319 Intellectual Property Statement 1321 The IETF takes no position regarding the validity or scope of any 1322 Intellectual Property Rights or other rights that might be claimed to 1323 pertain to the implementation or use of the technology described in 1324 this document or the extent to which any license under such rights 1325 might or might not be available; nor does it represent that it has 1326 made any independent effort to identify any such rights. 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