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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force Luca Martini Ed. 3 Internet Draft Giles Heron Ed. 4 Intended status: Standards Track 5 Expires: December 19, 2015 Cisco 7 June 19, 2015 9 Pseudowire Setup and Maintenance using the Label Distribution Protocol 11 draft-ietf-pals-rfc4447bis-01.txt 13 Status of this Memo 15 This Internet-Draft is submitted to IETF in full conformance with the 16 provisions of BCP 78 and BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on December 19, 2015 36 Abstract 38 Layer 2 services (such as Frame Relay, Asynchronous Transfer Mode, 39 and Ethernet) can be "emulated" over an MPLS backbone by 40 encapsulating the Layer 2 Protocol Data Units (PDU) and then 41 transmitting them over "pseudowires". It is also possible to use 42 pseudowires to provide low-rate Time Division Multiplexed and 43 Synchronous Optical NETworking circuit emulation over an MPLS-enabled 44 network. This document specifies a protocol for establishing and 45 maintaining the pseudowires, using extensions to the Label 46 Distribution Protocol (LDP). Procedures for encapsulating Layer 2 47 PDUs are specified in a set of companion documents. 49 This document has been written to address errata in a previous 50 version of this standard. 52 Table of Contents 54 1 Introduction ......................................... 4 55 2 Specification of Requirements ........................ 6 56 3 The Pseudowire Label ................................. 6 57 4 Details Specific to Particular Emulated Services ..... 8 58 4.1 IP Layer 2 Transport ................................. 8 59 5 LDP .................................................. 8 60 5.1 The PWid FEC Element ................................. 9 61 5.2 The Generalized PWid FEC Element ..................... 11 62 5.2.1 Attachment Identifiers ............................... 11 63 5.2.2 Encoding the Generalized PWid FEC Element ............ 13 64 5.2.2.1 Interface Parameters TLV ............................. 14 65 5.2.2.2 PW Grouping ID TLV ................................... 14 66 5.2.3 Signaling Procedures ................................. 15 67 5.3 Signaling of Pseudowire Status ....................... 16 68 5.3.1 Use of Label Mapping Messages ........................ 16 69 5.3.2 Signaling PW Status .................................. 17 70 5.3.3 Pseudowire Status Negotiation Procedures ............. 18 71 5.4 Interface Parameters Sub-TLV ......................... 20 72 5.5 LDP label Withdrawal procedures ...................... 21 73 6 Control Word ......................................... 21 74 6.1 PW Types for which the Control Word is REQUIRED ...... 21 75 6.2 PW Types for which the Control Word is NOT mandatory . 21 76 6.3 Control-Word Renegotiation by Label Request Message .. 23 77 6.4 Sequencing Considerations ............................ 24 78 6.4.1 Label Advertisements ................................. 24 79 6.4.2 Label Release ........................................ 24 80 7 IANA Considerations .................................. 25 81 7.1 LDP TLV TYPE ......................................... 25 82 7.2 LDP Status Codes ..................................... 25 83 7.3 FEC Type Name Space .................................. 25 84 8 Security Considerations .............................. 25 85 8.1 Data-Plane Security .................................. 25 86 8.2 Control-Plane Security ............................... 27 87 9 Changes from RFC4447 ................................. 28 88 10 Acknowledgments ...................................... 28 89 11 Normative References ................................. 28 90 12 Informative References ............................... 28 91 13 Author Information ................................... 29 92 14 Additional Historical Contributing Authors ........... 30 94 1. Introduction 96 [RFC4619], [RFC4717], [RFC4618], and [RFC4448] explain how to 97 encapsulate a Layer 2 Protocol Data Unit (PDU) for transmission over 98 an MPLS-enabled network. Those documents specify that a "pseudowire 99 header", consisting of a demultiplexor field, will be prepended to 100 the encapsulated PDU. The pseudowire demultiplexor field is 101 prepended before transmitting a packet on a pseudowire. When the 102 packet arrives at the remote endpoint of the pseudowire, the 103 demultiplexor is what enables the receiver to identify the particular 104 pseudowire on which the packet has arrived. To transmit the packet 105 from one pseudowire endpoint to another, the packet may need to 106 travel through a "Packet Switched Network (PSN) tunnel"; this will 107 require that an additional header be prepended to the packet. 109 Accompanying documents [RFC4842], [RFC4553] specify methods for 110 transporting time-division multiplexing (TDM) digital signals (TDM 111 circuit emulation) over a packet-oriented MPLS-enabled network. The 112 transmission system for circuit-oriented TDM signals is the 113 Synchronous Optical Network [ANSI] (SONET)/Synchronous Digital 114 Hierarchy (SDH) [ITUG]. To support TDM traffic, which includes 115 voice, data, and private leased-line service, the pseudowires must 116 emulate the circuit characteristics of SONET/SDH payloads. The TDM 117 signals and payloads are encapsulated for transmission over 118 pseudowires. A pseudowire demultiplexor and a PSN tunnel header is 119 prepended to this encapsulation. 121 [RFC4553] describes methods for transporting low-rate time-division 122 multiplexing (TDM) digital signals (TDM circuit emulation) over PSNs, 123 while [RFC4842] similarly describes transport of high-rate TDM 124 (SONET/SDH). To support TDM traffic, the pseudowires must emulate 125 the circuit characteristics of the original T1, E1, T3, E3, SONET, or 126 SDH signals. [RFC4553] does this by encapsulating an arbitrary but 127 constant amount of the TDM data in each packet, and the other methods 128 encapsulate TDM structures. 130 In this document, we specify the use of the MPLS Label Distribution 131 Protocol, LDP [RFC5036], as a protocol for setting up and maintaining 132 the pseudowires. In particular, we define new TLVs, FEC elements, 133 parameters, and codes for LDP, which enable LDP to identify 134 pseudowires and to signal attributes of pseudowires. We specify how 135 a pseudowire endpoint uses these TLVs in LDP to bind a demultiplexor 136 field value to a pseudowire, and how it informs the remote endpoint 137 of the binding. We also specify procedures for reporting pseudowire 138 status changes, for passing additional information about the 139 pseudowire as needed, and for releasing the bindings. These 140 procedures are intended to be independent of the underlying version 141 of IP used for LDP signaling. 143 In the protocol specified herein, the pseudowire demultiplexor field 144 is an MPLS label. Thus, the packets that are transmitted from one 145 end of the pseudowire to the other are MPLS packets, which must be 146 transmitted through an MPLS tunnel. However, if the pseudowire 147 endpoints are immediately adjacent and penultimate hop popping 148 behavior is in use, the MPLS tunnel may not be necessary. Any sort 149 of PSN tunnel can be used, as long as it is possible to transmit MPLS 150 packets through it. The PSN tunnel can itself be an MPLS LSP, or any 151 other sort of tunnel that can carry MPLS packets. Procedures for 152 setting up and maintaining the MPLS tunnels are outside the scope of 153 this document. 155 This document deals only with the setup and maintenance of point-to- 156 point pseudowires. Neither point-to-multipoint nor multipoint-to- 157 point pseudowires are discussed. 159 QoS-related issues are not discussed in this document. 161 The following two figures describe the reference models that are 162 derived from [RFC3985] to support the PW emulated services. 164 |<-------------- Emulated Service ---------------->| 165 | | 166 | |<------- Pseudowire ------->| | 167 | | | | 168 |Attachment| |<-- PSN Tunnel -->| |Attachment| 169 | Circuit V V V V Circuit | 170 V (AC) +----+ +----+ (AC) V 171 +-----+ | | PE1|==================| PE2| | +-----+ 172 | |----------|............PW1.............|----------| | 173 | CE1 | | | | | | | | CE2 | 174 | |----------|............PW2.............|----------| | 175 +-----+ ^ | | |==================| | | ^ +-----+ 176 ^ | +----+ +----+ | | ^ 177 | | Provider Edge 1 Provider Edge 2 | | 178 | | | | 179 Customer | | Customer 180 Edge 1 | | Edge 2 181 | | 182 native service native service 184 Figure 1: PWE3 Reference Model 186 +-----------------+ +-----------------+ 187 |Emulated Service | |Emulated Service | 188 |(e.g., TDM, ATM) |<==== Emulated Service ===>|(e.g., TDM, ATM) | 189 +-----------------+ +-----------------+ 190 | Payload | | Payload | 191 | Encapsulation |<====== Pseudowire =======>| Encapsulation | 192 +-----------------+ +-----------------+ 193 |PW Demultiplexer | |PW Demultiplexer | 194 | PSN Tunnel, |<======= PSN Tunnel ======>| PSN Tunnel, | 195 | PSN & Physical | | PSN & Physical | 196 | Layers | | Layers | 197 +-------+---------+ ___________ +---------+-------+ 198 | / | 199 +===============/ PSN ===============+ 200 / 201 _____________/ 203 Figure 2: PWE3 Protocol Stack Reference Model 205 For the purpose of this document, PE1 will be defined as the ingress 206 router, and PE2 as the egress router. A layer 2 PDU will be received 207 at PE1, encapsulated at PE1, transported and decapsulated at PE2, and 208 transmitted out of PE2. 210 Note that this document was written to address errata in [RFC4447]. 212 2. Specification of Requirements 214 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 215 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 216 document are to be interpreted as described in [RFC2119]. 218 3. The Pseudowire Label 220 Suppose that it is desired to transport Layer 2 PDUs from ingress LSR 221 PE1 to egress LSR PE2, across an intervening MPLS-enabled network. 222 We assume that there is an MPLS tunnel from PE1 to PE2. That is, we 223 assume that PE1 can cause a packet to be delivered to PE2 by 224 encapsulating the packet in an "MPLS tunnel header" and sending the 225 result to one of its adjacencies. The MPLS tunnel is an MPLS Label 226 Switched Path (LSP); thus, putting on an MPLS tunnel encapsulation is 227 a matter of pushing on an MPLS label. 229 We presuppose that a large number of pseudowires can be carried 230 through a single MPLS tunnel. Thus it is never necessary to maintain 231 state in the network core for individual pseudowires. We do not 232 presuppose that the MPLS tunnels are point to point; although the 233 pseudowires are point to point, the MPLS tunnels may be multipoint to 234 point. We do not presuppose that PE2 will even be able to determine 235 the MPLS tunnel through which a received packet was transmitted. 236 (For example, if the MPLS tunnel is an LSP and penultimate hop 237 popping is used, when the packet arrives at PE2, it will contain no 238 information identifying the tunnel.) 240 When PE2 receives a packet over a pseudowire, it must be able to 241 determine that the packet was in fact received over a pseudowire, and 242 it must be able to associate that packet with a particular 243 pseudowire. PE2 is able to do this by examining the MPLS label that 244 serves as the pseudowire demultiplexor field shown in Figure 2. Call 245 this label the "PW label". 247 When PE1 sends a Layer 2 PDU to PE2, it creates an MPLS packet by 248 adding the PW label to the packet, thus creating the first entry of 249 the label stack. If the PSN tunnel is an MPLS LSP, the PE1 pushes 250 another label (the tunnel label) onto the packet as the second entry 251 of the label stack. The PW label is not visible again until the MPLS 252 packet reaches PE2. PE2's disposition of the packet is based on the 253 PW label. 255 If the payload of the MPLS packet is, for example, an ATM AAL5 PDU, 256 the PW label will generally correspond to a particular ATM VC at PE2. 257 That is, PE2 needs to be able to infer from the PW label the outgoing 258 interface and the VPI/VCI value for the AAL5 PDU. If the payload is 259 a Frame Relay PDU, then PE2 needs to be able to infer from the PW 260 label the outgoing interface and the DLCI value. If the payload is 261 an Ethernet frame, then PE2 needs to be able to infer from the PW 262 label the outgoing interface, and perhaps the VLAN identifier. This 263 process is uni-directional and will be repeated independently for 264 bi-directional operation. When using the PWid FEC Element, it is 265 REQUIRED that the same PW ID and PW type be assigned for a given 266 circuit in both directions. The group ID (see below) MUST NOT be 267 required to match in both directions. The transported frame MAY be 268 modified when it reaches the egress router. If the header of the 269 transported Layer 2 frame is modified, this MUST be done at the 270 egress LSR only. Note that the PW label must always be at the bottom 271 of the packet's label stack, and labels MUST be allocated from the 272 per-platform label space. 274 This document does not specify a method for distributing the MPLS 275 tunnel label or any other labels that may appear above the PW label 276 on the stack. Any acceptable method of MPLS label distribution will 277 do. This document specifies a protocol for assigning and 278 distributing the PW label. This protocol is LDP, extended as 279 specified in the remainder of this document. An LDP session must be 280 set up between the pseudowire endpoints. LDP MUST exchange PW FEC 281 label bindings in downstream unsolicited manner, independent of the 282 negotiated label advertisement mode of the LDP session according to 283 the specifications in specified in [RFC7358]. LDP's "liberal label 284 retention" mode SHOULD be used. 286 In addition to the protocol specified herein, static assignment of PW 287 labels may be used, and implementations of this protocol SHOULD 288 provide support for static assignment. PW encapsulation is always 289 symmetrical in both directions of traffic along a specific PW, 290 whether the PW uses an LDP control plane or not. 292 This document specifies all the procedures necessary to set up and 293 maintain the pseudowires needed to support "unswitched" point to 294 point services, where each endpoint of the pseudowire is provisioned 295 with the identity of the other endpoint. There are also protocol 296 mechanisms specified herein that can be used to support switched 297 services and other provisioning models. However, the use of the 298 protocol mechanisms to support those other models and services is not 299 described in this document. 301 4. Details Specific to Particular Emulated Services 303 4.1. IP Layer 2 Transport 305 This mode carries IP packets over a pseudowire. The encapsulation 306 used is according to [RFC3032]. The PW control word MAY be inserted 307 between the MPLS label stack and the IP payload. The encapsulation 308 of the IP packets for forwarding on the attachment circuit is 309 implementation specific, is part of the native service processing 310 (NSP) function [RFC3985], and is outside the scope of this document. 312 5. LDP 314 The PW label bindings are distributed using the LDP downstream 315 unsolicited mode described in [RFC5036]. The PEs will establish an 316 LDP session using the Extended Discovery mechanism described in [LDP, 317 sectionn 2.4.2 and 2.5]. 319 An LDP Label Mapping message contains an FEC TLV, a Label TLV, and 320 zero or more optional parameter TLVs. 322 The FEC TLV is used to indicate the meaning of the label. In the 323 current context, the FEC TLV would be used to identify the particular 324 pseudowire that a particular label is bound to. In this 325 specification, we define two new FEC TLVs to be used for identifying 326 pseudowires. When setting up a particular pseudowire, only one of 327 these FEC TLVs is used. The one to be used will depend on the 328 particular service being emulated and on the particular provisioning 329 model being supported. 331 LDP allows each FEC TLV to consist of a set of FEC elements. For 332 setting up and maintaining pseudowires, however, each FEC TLV MUST 333 contain exactly one FEC element. 335 The LDP base specification has several kinds of label TLVs, including 336 the Generic Label TLV, as specified in [RFC5036], section 3.4.2.1. 337 For setting up and maintaining pseudowires, the Generic Label TLV 338 MUST be used. 340 5.1. The PWid FEC Element 342 The PWid FEC element may be used whenever both pseudowire endpoints 343 have been provisioned with the same 32-bit identifier for the 344 pseudowire. 346 For this purpose, a new type of FEC element is defined. The FEC 347 element type is 0x80 and is defined as follows: 349 0 1 2 3 350 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 351 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 352 | PWid (0x80) |C| PW type |PW info Length | 353 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 354 | Group ID | 355 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 356 | PW ID | 357 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 358 | Interface Parameter Sub-TLV | 359 | " | 360 | " | 361 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 363 - PW type 365 A 15 bit quantity containing a value that represents the type of 366 PW. Assigned Values are specified in "IANA Allocations for 367 pseudo Wire Edge to Edge Emulation (PWE3)" [RFC4446]. 369 - Control word bit (C) 371 The bit (C) is used to flag the presence of a control word as 372 follows: 374 C = 1 control word present on this PW. 375 C = 0 no control word present on this PW. 377 Please see the section "Control Word" for further explanation. 379 - PW information length 381 Length of the PW ID field and the interface parameters sub-TLV in 382 octets. If this value is 0, then it references all PWs using the 383 specified group ID, and there is no PW ID present, nor are there 384 any interface parameter sub-TLVs. 386 - Group ID 388 An arbitrary 32 bit value which represents a group of PWs that is 389 used to create groups in the PW space. The group ID is intended 390 to be used as a port index, or a virtual tunnel index. To 391 simplify configuration a particular PW ID at ingress could be 392 part of a Group ID assigned to the virtual tunnel for transport 393 to the egress router. The Group ID is very useful for sending 394 wild card label withdrawals, or PW wild card status notification 395 messages to remote PEs upon physical port failure. 397 - PW ID 399 A non-zero 32-bit connection ID that together with the PW type 400 identifies a particular PW. Note that the PW ID and the PW type 401 MUST be the same at both endpoints. 403 - Interface Parameter Sub-TLV 405 This variable length TLV is used to provide interface specific 406 parameters, such as attachment circuit MTU. 408 Note that as the "interface parameter sub-TLV" is part of the 409 FEC, the rules of LDP make it impossible to change the interface 410 parameters once the pseudowire has been set up. Thus the 411 interface parameters field must not be used to pass information, 412 such as status information, that may change during the life of 413 the pseudowire. Optional parameter TLVs should be used for that 414 purpose. 416 Using the PWid FEC, each of the two pseudowire endpoints 417 independently initiates the setup of a unidirectional LSP. An 418 outgoing LSP and an incoming LSP are bound together into a single 419 pseudowire if they have the same PW ID and PW type. 421 5.2. The Generalized PWid FEC Element 423 The PWid FEC element can be used if a unique 32-bit value has been 424 assigned to the PW, and if each endpoint has been provisioned with 425 that value. The Generalized PWid FEC element requires that the PW 426 endpoints be uniquely identified; the PW itself is identified as a 427 pair of endpoints. In addition, the endpoint identifiers are 428 structured to support applications where the identity of the remote 429 endpoints needs to be auto-discovered rather than statically 430 configured. 432 The "Generalized PWid FEC Element" is FEC type 0x81. 434 The Generalized PWid FEC Element does not contain anything 435 corresponding to the "Group ID" of the PWid FEC element. The 436 functionality of the "Group ID" is provided by a separate optional 437 LDP TLV, the "PW Grouping TLV", described below. The Interface 438 Parameters field of the PWid FEC element is also absent; its 439 functionality is replaced by the optional Interface Parameters TLV, 440 described below. 442 5.2.1. Attachment Identifiers 444 As discussed in [RFC3985], a pseudowire can be thought of as 445 connecting two "forwarders". The protocol used to set up a 446 pseudowire must allow the forwarder at one end of a pseudowire to 447 identify the forwarder at the other end. We use the term "attachment 448 identifier", or "AI", to refer to the field that the protocol uses to 449 identify the forwarders. In the PWid FEC, the PWid field serves as 450 the AI. In this section, we specify a more general form of AI that 451 is structured and of variable length. 453 Every Forwarder in a PE must be associated with an Attachment 454 Identifier (AI), either through configuration or through some 455 algorithm. The Attachment Identifier must be unique in the context 456 of the PE router in which the Forwarder resides. The combination must be globally unique. 459 It is frequently convenient to regard a set of Forwarders as being 460 members of a particular "group", where PWs may only be set up among 461 members of a group. In such cases, it is convenient to identify the 462 Forwarders relative to the group, so that an Attachment Identifier 463 would consist of an Attachment Group Identifier (AGI) plus an 464 Attachment Individual Identifier (AII). 466 An Attachment Group Identifier may be thought of as a VPN-id, or a 467 VLAN identifier, some attribute that is shared by all the Attachment 468 PWs (or pools thereof) that are allowed to be connected. 470 The details of how to construct the AGI and AII fields identifying 471 the pseudowire endpoints are outside the scope of this specification. 472 Different pseudowire applications, and different provisioning models, 473 will require different sorts of AGI and AII fields. The 474 specification of each such application and/or model must include the 475 rules for constructing the AGI and AII fields. 477 As previously discussed, a (bidirectional) pseudowire consists of a 478 pair of unidirectional LSPs, one in each direction. If a particular 479 pseudowire connects PE1 with PE2, the PW direction from PE1 to PE2 480 can be identified as: 482 , PE2, >, 484 and the PW direction from PE2 to PE1 can be identified by: 486 , PE1, >. 488 Note that the AGI must be the same at both endpoints, but the AII 489 will in general be different at each endpoint. Thus, from the 490 perspective of a particular PE, each pseudowire has a local or 491 "Source AII", and a remote or "Target AII". The pseudowire setup 492 protocol can carry all three of these quantities: 494 - Attachment Group Identifier (AGI). 496 - Source Attachment Individual Identifier (SAII) 498 - Target Attachment Individual Identifier (TAII) 500 If the AGI is non-null, then the Source AI (SAI) consists of the AGI 501 together with the SAII, and the Target AI (TAI) consists of the TAII 502 together with the AGI. If the AGI is null, then the SAII and TAII 503 are the SAI and TAI, respectively. 505 The interpretation of the SAI and TAI is a local matter at the 506 respective endpoint. 508 The association of two unidirectional LSPs into a single 509 bidirectional pseudowire depends on the SAI and the TAI. Each 510 application and/or provisioning model that uses the Generalized PWid 511 FEC element must specify the rules for performing this association. 513 5.2.2. Encoding the Generalized PWid FEC Element 515 FEC element type 0x81 is used. The FEC element is encoded as 516 follows: 518 0 1 2 3 519 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 521 |Gen PWid (0x81)|C| PW Type |PW info Length | 522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 523 | AGI Type | Length | Value | 524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 525 ~ AGI Value (contd.) ~ 526 | | 527 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 528 | AII Type | Length | Value | 529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 530 ~ SAII Value (contd.) ~ 531 | | 532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 533 | AII Type | Length | Value | 534 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 535 ~ TAII Value (contd.) ~ 536 | | 537 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 539 This document does not specify the AII and AGI type field values; 540 specification of the type field values to be used for a particular 541 application is part of the specification of that application. IANA 542 has assigned these values using the method defined in the [RFC4446] 543 document. 545 The SAII, TAII, and AGI are simply carried as octet strings. The 546 length byte specifies the size of the Value field. The null string 547 can be sent by setting the length byte to 0. If a particular 548 application does not need all three of these sub-elements, it MUST 549 send all the sub-elements but set the length to 0 for the unused 550 sub-elements. 552 The PW information length field contains the length of the SAII, 553 TAII, and AGI, combined in octets. If this value is 0, then it 554 references all PWs using the specific grouping ID (specified in the 555 PW grouping ID TLV). In this case, there are no other FEC element 556 fields (AGI, SAII, etc.) present, nor any interface parameters TLVs. 558 Note that the interpretation of a particular field as AGI, SAII, or 559 TAII depends on the order of its occurrence. The type field 560 identifies the type of the AGI, SAII, or TAII. When comparing two 561 occurrences of an AGI (or SAII or TAII), the two occurrences are 562 considered identical if the type, length, and value fields of one are 563 identical, respectively, to those of the other. 565 5.2.2.1. Interface Parameters TLV 567 This TLV MUST only be used when sending the Generalized PW FEC. It 568 specifies interface-specific parameters. Specific parameters, when 569 applicable, MUST be used to validate that the PEs and the ingress and 570 egress ports at the edges of the circuit have the necessary 571 capabilities to interoperate with each other. 573 0 1 2 3 574 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 575 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 576 |0|0| PW Intf P. TLV (0x096B) | Length | 577 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 578 | Sub-TLV Type | Length | Variable Length Value | 579 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 580 | Variable Length Value | 581 | " | 582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 584 A more detailed description of this field can be found in the section 585 "Interface Parameters Sub-TLV", below. 587 5.2.2.2. PW Grouping ID TLV 589 0 1 2 3 590 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 592 |0|0|PW Grouping ID TLV (0x096C)| Length | 593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 594 | Value | 595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 597 The PW Grouping ID is an arbitrary 32-bit value that represents an 598 arbitrary group of PWs. It is used to create group PWs; for example, 599 a PW Grouping ID can be used as a port index and assigned to all PWs 600 that lead to that port. Use of the PW Grouping ID enables one to 601 send "wild card" label withdrawals, or "wild card" status 602 notification messages, to remote PEs upon physical port failure. 604 Note Well: The PW Grouping ID is different from and has no relation 605 to, the Attachment Group Identifier. 607 The PW Grouping ID TLV is not part of the FEC and will not be 608 advertised except in the PW FEC advertisement. The advertising PE 609 MAY use the wild card withdraw semantics, but the remote PEs MUST 610 implement support for wild card messages. This TLV MUST only be used 611 when sending the Generalized PW ID FEC. 613 To issue a wild card command (status or withdraw): 615 - Set the PW Info Length to 0 in the Generalized PWid FEC Element. 616 - Send only the PW Grouping ID TLV with the FEC (no AGI/SAII/TAII 617 is sent). 619 5.2.3. Signaling Procedures 621 In order for PE1 to begin signaling PE2, PE1 must know the address of 622 the remote PE2, and a TAI. This information may have been configured 623 at PE1, or it may have been learned dynamically via some 624 autodiscovery procedure. 626 The egress PE (PE1), which has knowledge of the ingress PE, initiates 627 the setup by sending a Label Mapping Message to the ingress PE (PE2). 628 The Label Mapping message contains the FEC TLV, carrying the 629 Generalized PWid FEC Element (type 0x81). The Generalized PWid FEC 630 element contains the AGI, SAII, and TAII information. 632 Next, when PE2 receives such a Label Mapping message, PE2 interprets 633 the message as a request to set up a PW whose endpoint (at PE2) is 634 the Forwarder identified by the TAI. From the perspective of the 635 signaling protocol, exactly how PE2 maps AIs to Forwarders is a local 636 matter. In some Virtual Private Wire Services (VPWS) provisioning 637 models, the TAI might, for example, be a string that identifies a 638 particular Attachment Circuit, such as "ATM3VPI4VCI5", or it might, 639 for example, be a string, such as "Fred", that is associated by 640 configuration with a particular Attachment Circuit. In VPLS, the AGI 641 could be a VPN-id, identifying a particular VPLS instance. 643 If PE2 cannot map the TAI to one of its Forwarders, then PE2 sends a 644 Label Release message to PE1, with a Status Code of 645 "Unassigned/Unrecognized TAI", and the processing of the Label 646 Mapping message is complete. 648 The FEC TLV sent in a Label Release message is the same as the FEC 649 TLV received in the Label Mapping being released (but without the 650 interface parameter TLV). More generally, the FEC TLV is the same in 651 all LDP messages relating to the same PW. In a Label Release this 652 means that the SAII is the remote peer's AII and the TAII is the 653 sender's local AII. 655 If the Label Mapping Message has a valid TAI, PE2 must decide whether 656 to accept it. The procedures for so deciding will depend on the 657 particular type of Forwarder identified by the TAI. Of course, the 658 Label Mapping message may be rejected due to standard LDP error 659 conditions as detailed in [RFC5036]. 661 If PE2 decides to accept the Label Mapping message, then it has to 662 make sure that a PW LSP is set up in the opposite (PE1-->PE2) 663 direction. If it has already signaled for the corresponding PW LSP 664 in that direction, nothing more needs to be done. Otherwise, it must 665 initiate such signaling by sending a Label Mapping message to PE1. 666 This is very similar to the Label Mapping message PE2 received, but 667 the SAI and TAI are reversed. 669 Thus, a bidirectional PW consists of two LSPs, where the FEC of one 670 has the SAII and TAII reversed with respect to the FEC of the other. 672 5.3. Signaling of Pseudowire Status 674 5.3.1. Use of Label Mapping Messages 676 The PEs MUST send Label Mapping Messages to their peers as soon as 677 the PW is configured and administratively enabled, regardless of the 678 attachment circuit state. The PW label should not be withdrawn 679 unless the operator administratively configures the pseudowire down 680 (or the PW configuration is deleted entirely). Using the procedures 681 outlined in this section, a simple label withdraw method MAY also be 682 supported as a legacy means of signaling PW status and AC status. In 683 any case, if the label-to-PW binding is not available the PW MUST be 684 considered in the down state. 686 Once the PW status negotiation procedures are completed and if they 687 result in the use of the label withdraw method for PW status 688 communication, and this method is not supported by one of the PEs, 689 then that PE must send a Label Release Message to its peer with the 690 following error: 692 "Label Withdraw PW Status Method Not Supported" 694 If the label withdraw method for PW status communication is selected 695 for the PW, it will result in the Label Mapping Message being 696 advertised only if the attachment circuit is active. The PW status 697 signaling procedures described in this section MUST be fully 698 implemented. 700 5.3.2. Signaling PW Status 702 The PE devices use an LDP TLV to indicate status to their remote 703 peers. This PW Status TLV contains more information than the 704 alternative simple Label Withdraw message. 706 The format of the PW Status TLV is: 707 0 1 2 3 708 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 710 |1|0| PW Status (0x096A) | Length | 711 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 712 | Status Code | 713 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 715 The status code is a 4 octet bit field as specified in the PW IANA 716 Allocations document [RFC4446]. The length specifies the length of 717 the Status Code field in octets (equal to 4). 719 Each bit in the status code field can be set individually to indicate 720 more than a single failure at once. Each fault can be cleared by 721 sending an appropriate Notification message in which the respective 722 bit is cleared. The presence of the lowest bit (PW Not Forwarding) 723 acts only as a generic failure indication when there is a link-down 724 event for which none of the other bits apply. 726 The Status TLV is transported to the remote PW peer via the LDP 727 Notification message. The general format of the Notification Message 728 is: 730 0 1 2 3 731 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 732 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 733 |0| Notification (0x0001) | Message Length | 734 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 735 | Message ID | 736 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 737 | Status (TLV) | 738 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 739 | PW Status TLV | 740 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 741 | PWId FEC TLV or Generalized ID FEC TLV | 742 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 743 | PW Grouping ID TLV (Optional) | 744 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 745 The Status TLV status code is set to 0x00000028, "PW status", to 746 indicate that PW status follows. Since this notification does not 747 refer to any particular message, the Message Id and Message Type 748 fields are set to 0. 750 The PW FEC TLV SHOULD NOT include the interface parameter sub-TLVs, 751 as they are ignored in the context of this message. However the PW 752 FEC TLV MUST include the C bit, where aplicable, as it is part of the 753 FEC. When a PE's attachment circuit encounters an error, use of the 754 PW Notification Message allows the PE to send a single "wild card" 755 status message, using a PW FEC TLV with only the group ID set, to 756 denote this change in status for all affected PW connections. This 757 status message contains either the PW FEC TLV with only the group ID 758 set, or else it contains the Generalized FEC TLV with only the PW 759 Grouping ID TLV. 761 As mentioned above, the Group ID field of the PWid FEC element, or 762 the PW Grouping ID TLV used with the Generalized PWid FEC element, 763 can be used to send a status notification for all arbitrary sets of 764 PWs. This procedure is OPTIONAL, and if it is implemented, the LDP 765 Notification message should be as follows: If the PWid FEC element is 766 used, the PW information length field is set to 0, the PW ID field is 767 not present, and the interface parameter sub-TLVs are not present. 768 If the Generalized FEC element is used, the AGI, SAII, and TAII are 769 not present, the PW information length field is set to 0, the PW 770 Grouping ID TLV is included, and the Interface Parameters TLV is 771 omitted. For the purpose of this document, this is called the "wild 772 card PW status notification procedure", and all PEs implementing this 773 design are REQUIRED to accept such a notification message but are not 774 required to send it. 776 5.3.3. Pseudowire Status Negotiation Procedures 778 When a PW is first set up, the PEs MUST attempt to negotiate the 779 usage of the PW status TLV. This is accomplished as follows: A PE 780 that supports the PW Status TLV MUST include it in the initial Label 781 Mapping message following the PW FEC and the interface parameter 782 sub-TLVs. The PW Status TLV will then be used for the lifetime of 783 the pseudowire. This is shown in the following diagram: 785 0 1 2 3 786 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 787 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 788 | | 789 + PWId FEC or Generalized ID FEC + 790 | | 791 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 792 | Interface Parameters | 793 | " | 794 | " | 795 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 796 |0|0| Generic Label (0x0200) | Length | 797 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 798 | Label | 799 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 800 |1|0| PW Status (0x096A) | Length | 801 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 802 | Status Code | 803 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 805 If a PW Status TLV is included in the initial Label Mapping message 806 for a PW, then if the Label Mapping message from the remote PE for 807 that PW does not include a PW status TLV, or if the remote PE does 808 not support the PW Status TLV, the PW will revert to the label 809 withdraw method of signaling PW status. Note that if the PW Status 810 TLV is not supported by the remote peer, the peer will automatically 811 ignore it, since the I (ignore) bit is set in the TLV. The PW Status 812 TLV, therefore, will not be present in the corresponding FEC 813 advertisement from the remote LDP peer, which results in exactly the 814 above behavior. 816 If the PW Status TLV is not present following the FEC TLV in the 817 initial PW Label Mapping message received by a PE, then the PW Status 818 TLV will not be used, and both PEs supporting the pseudowire will 819 revert to the label withdraw procedure for signaling status changes. 821 If the negotiation process results in the usage of the PW status TLV, 822 then the actual PW status is determined by the PW status TLV that was 823 sent within the initial PW Label Mapping message. Subsequent updates 824 of PW status are conveyed through the notification message. 826 5.4. Interface Parameters Sub-TLV 828 This field specifies interface-specific parameters. When applicable, 829 it MUST be used to validate that the PEs and the ingress and egress 830 ports at the edges of the circuit have the necessary capabilities to 831 interoperate with each other. The field structure is defined as 832 follows: 834 0 1 2 3 835 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 836 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 837 | Sub-TLV Type | Length | Variable Length Value | 838 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 839 | Variable Length Value | 840 | " | 841 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 843 The interface parameter sub-TLV type values are specified in "IANA 844 Allocations for Pseudowire Edge to Edge Emulation (PWE3)" [RFC4446]. 846 The Length field is defined as the length of the interface parameter 847 including the parameter id and length field itself. Processing of 848 the interface parameters should continue when unknown interface 849 parameters are encountered, and they MUST be silently ignored. 851 - Interface MTU sub-TLV type 853 A 2 octet value indicating the MTU in octets. This is the 854 Maximum Transmission Unit, excluding encapsulation overhead, of 855 the egress packet interface that will be transmitting the 856 decapsulated PDU that is received from the MPLS-enabled network. 857 This parameter is applicable only to PWs transporting packets and 858 is REQUIRED for these PW types. If this parameter does not match 859 in both directions of a specific PW, that PW MUST NOT be enabled. 861 - Optional Interface Description string sub-TLV type 863 This arbitrary, and OPTIONAL, interface description string is 864 used to send a human-readable administrative string describing 865 the interface to the remote. This parameter is OPTIONAL, and is 866 applicable to all PW types. The interface description parameter 867 string length is variable, and can be from 0 to 80 octets. 868 Human-readable text MUST be provided in the UTF-8 charset using 869 the Default Language [RFC2277]. 871 5.5. LDP label Withdrawal procedures 873 As mentioned above, the Group ID field of the PWid FEC element, or 874 the PW Grouping ID TLV used with the Generalized PWid FEC element, 875 can be used to withdraw all PW labels associated with a particular PW 876 group. This procedure is OPTIONAL, and if it is implemented, the LDP 877 Label Withdraw message should be as follows: If the PWid FEC element 878 is used, the PW information length field is set to 0, the PW ID field 879 is not present, the interface parameter sub-TLVs are not present, and 880 the Label TLV is not present. If the Generalized FEC element is 881 used, the AGI, SAII, and TAII are not present, the PW information 882 length field is set to 0, the PW Grouping ID TLV is included, the 883 Interface Parameters TLV is not present, and the Label TLV is not 884 present. For the purpose of this document, this is called the "wild 885 card withdraw procedure", and all PEs implementing this design are 886 REQUIRED to accept such withdrawn message but are not required to 887 send it. Note that the PW Grouping ID TLV only applies to PWs using 888 the Generalized ID FEC element, while the Group ID only applies to 889 PWid FEC element. 891 The interface parameter sub-TLVs, or TLV, MUST NOT be present in any 892 LDP PW Label Withdraw or Label Release message. A wild card Label 893 Release message MUST include only the group ID, or Grouping ID TLV. 894 A Label Release message initiated by a PE router must always include 895 the PW ID. 897 6. Control Word 899 6.1. PW Types for which the Control Word is REQUIRED 901 The Label Mapping messages that are sent in order to set up these PWs 902 MUST have c=1. When a Label Mapping message for a PW of one of these 903 types is received and c=0, a Label Release message MUST be sent, with 904 an "Illegal C-bit" status code. In this case, the PW will not be 905 enabled. 907 6.2. PW Types for which the Control Word is NOT mandatory 909 If a system is capable of sending and receiving the control word on 910 PW types for which the control word is not mandatory, then each such 911 PW endpoint MUST be configurable with a parameter that specifies 912 whether the use of the control word is PREFERRED or NOT PREFERRED. 913 For each PW, there MUST be a default value of this parameter. This 914 specification does NOT state what the default value should be. 916 If a system is NOT capable of sending and receiving the control word 917 on PW types for which the control word is not mandatory, then it 918 behaves exactly as if it were configured for the use of the control 919 word to be NOT PREFERRED. 921 If a Label Mapping message for the PW has already been received but 922 no Label Mapping message for the PW has yet been sent, then the 923 procedure is as follows: 925 -i. If the received Label Mapping message has c=0, send a Label 926 Mapping message with c=0; the control word is not used. 927 -ii. If the received Label Mapping message has c=1, and the PW is 928 locally configured such that the use of the control word is 929 preferred, then send a Label Mapping message with c=1; the 930 control word is used. 931 -iii. If the received Label Mapping message has c=1, and the PW is 932 locally configured such that the use of the control word is 933 not preferred or the control word is not supported, then act 934 as if no Label Mapping message for the PW had been received 935 (That is: proceed to the next paragraph). 937 If a Label Mapping message for the PW has not already been received 938 (or if the received Label Mapping message had c=1 and either local 939 configuration says that the use of the control word is not preferred 940 or the control word is not supported), then send a Label Mapping 941 message in which the c bit is set to correspond to the locally 942 configured preference for use of the control word. (That is, set c=1 943 if locally configured to prefer the control word, and set c=0 if 944 locally configured to prefer not to use the control word or if the 945 control word is not supported). 947 The next action depends on what control message is next received for 948 that PW. The possibilities are as follows: 950 -i. A Label Mapping message with the same c bit value as 951 specified in the Label Mapping message that was sent. PW 952 setup is now complete, and the control word is used if c=1 953 but is not used if c=0. 955 -ii. A Label Mapping message with c=1, but the Label Mapping 956 message that was sent has c=0. In this case, ignore the 957 received Label Mapping message and continue to wait for the 958 next control message for the PW. 960 -iii. A Label Mapping message with c=0, but the Label Mapping 961 message that was sent has c=1. In this case, send a Label 962 Withdraw message with a "Wrong C-bit" status code, followed 963 by a Label Mapping message that has c=0. PW setup is now 964 complete, and the control word is not used. 966 -iv. A Label Withdraw message with the "Wrong c-bit" status code. 967 Treat as a normal Label Withdraw, but do not respond. 968 Continue to wait for the next control message for the PW. 970 If at any time after a Label Mapping message has been received a 971 corresponding Label Withdraw or Release is received, the action taken 972 is the same as for any Label Withdraw or Release that might be 973 received at any time. 975 If both endpoints prefer the use of the control word, this procedure 976 will cause it to be used. If either endpoint prefers not to use the 977 control word or does not support the control word, this procedure 978 will cause it not to be used. If one endpoint prefers to use the 979 control word but the other does not, the one that prefers not to use 980 it has no extra protocol to execute; it just waits for a Label 981 Mapping message that has c=0. 983 6.3. Control-Word Renegotiation by Label Request Message 985 It is possible that after the PW C-bit negotation procedure described 986 above is completed, the local PE is re-provisioned with a different 987 control word preference. Therefore once the Control-Word negotation 988 procedures are completed, the procedure can be restarted as follows: 989 -i. If local PE has previously sent a Label Mapping message, it 990 MUST send a Label Withdraw message to remote PE and wait 991 until it has received a Label Release message from the 992 remote PE. 993 -ii. the local PE MUST send a label release message to the remote 994 PE for the specific label associated with the FEC that was 995 advertized for this specific PW. Note: the above-mentioned 996 steps of the Label Release message and Label Withdraw 997 message are not required to be excuted in any specific 998 sequence. 999 -iii. The local PE MUST send a Label Request message to the peer 1000 PE, and then MUST wait until it receives a Label Mapping 1001 message containing the remote PE current configured 1002 preference for use of control word. 1004 Once the remote PE has successfully processed the Label Withdraw 1005 message and Label Release messages, it will reset the C-Bit 1006 negotation state machine and its use of control word with the locally 1007 configured preference. 1009 From this point on the local and remote PEs will follow the C-bit 1010 negotaiation procedures defined in the previous section. 1012 The above C-bit renegotation process SHOULD NOT be interupted until 1013 it is completed, or unpredictable results might occur. 1015 6.4. Sequencing Considerations 1017 In the case where the router considers the sequence number field in 1018 the control word, it is important to note the following details when 1019 advertising labels. 1021 6.4.1. Label Advertisements 1023 After a label has been withdrawn by the output router and/or released 1024 by the input router, care must be taken not to advertise (re-use) the 1025 same released label until the output router can be reasonably certain 1026 that old packets containing the released label no longer persist in 1027 the MPLS-enabled network. 1029 This precaution is required to prevent the imposition router from 1030 restarting packet forwarding with a sequence number of 1 when it 1031 receives a Label Mapping message that binds the same FEC to the same 1032 label if there are still older packets in the network with a sequence 1033 number between 1 and 32768. For example, if there is a packet with a 1034 sequence number=n, where n is in the interval [1,32768] traveling 1035 through the network, it would be possible for the disposition router 1036 to receive that packet after it re-advertises the label. Since the 1037 label has been released by the imposition router, the disposition 1038 router SHOULD be expecting the next packet to arrive with a sequence 1039 number of 1. Receipt of a packet with a sequence number equal to n 1040 will result in n packets potentially being rejected by the 1041 disposition router until the imposition router imposes a sequence 1042 number of n+1 into a packet. Possible methods to avoid this are for 1043 the disposition router always to advertise a different PW label, or 1044 for the disposition router to wait for a sufficient time before 1045 attempting to re-advertise a recently released label. This is only 1046 an issue when sequence number processing is enabled at the 1047 disposition router. 1049 6.4.2. Label Release 1051 In situations where the imposition router wants to restart forwarding 1052 of packets with sequence number 1, the router shall 1) send to the 1053 disposition router a Label Release Message, and 2) send to the 1054 disposition router a Label Request message. When sequencing is 1055 supported, advertisement of a PW label in response to a Label Request 1056 message MUST also consider the issues discussed in the section on 1057 Label Advertisements. 1059 7. IANA Considerations 1061 In general IANA needs to update any references in the registries 1062 referring to RFC4447 to this document. 1064 7.1. LDP TLV TYPE 1066 This document uses several new LDP TLV types; IANA already maintains 1067 a registry of name "TLV TYPE NAME SPACE" defined by RFC 5036. Any 1068 references to RFC4447 need to be updated to reference this document. 1070 7.2. LDP Status Codes 1072 This document uses several new LDP status codes; IANA already 1073 maintains a registry of name "STATUS CODE NAME SPACE" defined by RFC 1074 5036. Any references to RFC4447 need to be updated to reference this 1075 document. 1077 7.3. FEC Type Name Space 1079 This document uses two new FEC element types, 0x80 and 0x81, from the 1080 registry "FEC Type Name Space" for the Label Distribution Protocol 1081 (LDP RFC 5036). Any references to RFC4447 need to be updated to 1082 reference this document. 1084 8. Security Considerations 1086 This document specifies the LDP extensions that are needed for 1087 setting up and maintaining pseudowires. The purpose of setting up 1088 pseudowires is to enable Layer 2 frames to be encapsulated in MPLS 1089 and transmitted from one end of a pseudowire to the other. Therefore 1090 we treat the security considerations for both the data plane and the 1091 control plane. 1093 8.1. Data-Plane Security 1095 With regard to the security of the data plane, the following areas 1096 must be considered: 1098 - MPLS PDU inspection. 1099 - MPLS PDU spoofing. 1101 - MPLS PDU alteration. 1102 - MPLS PSN protocol security. 1103 - Access Circuit security. 1104 - Denial of service prevention on the PE routers. 1106 When an MPLS PSN is used to provide pseudowire service, there is a 1107 perception that security MUST be at least equal to the currently 1108 deployed Layer 2 native protocol networks that the MPLS/PW network 1109 combination is emulating. This means that the MPLS-enabled network 1110 SHOULD be isolated from outside packet insertion in such a way that 1111 it SHOULD NOT be possible to insert an MPLS packet into the network 1112 directly. To prevent unwanted packet insertion, it is also important 1113 to prevent unauthorized physical access to the PSN, as well as 1114 unauthorized administrative access to individual network elements. 1116 As mentioned above, an MPLS-enabled network should not accept MPLS 1117 packets from its external interfaces (i.e., interfaces to CE devices 1118 or to other providers' networks) unless the top label of the packet 1119 was legitimately distributed to the system from which the packet is 1120 being received. If the packet's incoming interface leads to a 1121 different SP (rather than to a customer), an appropriate trust 1122 relationship must also be present, including the trust that the other 1123 SP also provides appropriate security measures. 1125 The three main security problems faced when using an MPLS-enabled 1126 network to transport PWs are spoofing, alteration, and inspection. 1127 First, there is a possibility that the PE receiving PW PDUs will get 1128 a PDU that appears to be from the PE transmitting the PW into the 1129 PSN, but that was not actually transmitted by the PE originating the 1130 PW. (That is, the specified encapsulations do not by themselves 1131 enable the decapsulator to authenticate the encapsulator.) A second 1132 problem is the possibility that the PW PDU will be altered between 1133 the time it enters the PSN and the time it leaves the PSN (i.e., the 1134 specified encapsulations do not by themselves assure the decapsulator 1135 of the packet's integrity.) A third problem is the possibility that 1136 the PDU's contents will be seen while the PDU is in transit through 1137 the PSN (i.e., the specification encapsulations do not ensure 1138 privacy.) How significant these issues are in practice depends on 1139 the security requirements of the applications whose traffic is being 1140 sent through the tunnel, and how secure the PSN itself is. 1142 8.2. Control-Plane Security 1144 General security considerations with regard to the use of LDP are 1145 specified in section 5 of RFC 5036. Those considerations also apply 1146 to the case where LDP is used to set up pseudowires. 1148 A pseudowire connects two attachment circuits. It is important to 1149 make sure that LDP connections are not arbitrarily accepted from 1150 anywhere, or else a local attachment circuit might get connected to 1151 an arbitrary remote attachment circuit. Therefore, an incoming LDP 1152 session request MUST NOT be accepted unless its IP source address is 1153 known to be the source of an "eligible" LDP peer. The set of 1154 eligible peers could be pre-configured (either as a list of IP 1155 addresses, or as a list of address/mask combinations), or it could be 1156 discovered dynamically via an auto-discovery protocol that is itself 1157 trusted. (Obviously, if the auto-discovery protocol were not 1158 trusted, the set of "eligible peers" it produces could not be 1159 trusted.) 1161 Even if an LDP connection request appears to come from an eligible 1162 peer, its source address may have been spoofed. Therefore, some 1163 means of preventing source address spoofing must be in place. For 1164 example, if all the eligible peers are in the same network, source 1165 address filtering at the border routers of that network could 1166 eliminate the possibility of source address spoofing. 1168 The LDP MD5 authentication key option, as described in section 2.9 of 1169 RFC 5036, MUST be implemented, and for a greater degree of security, 1170 it must be used. This provides integrity and authentication for the 1171 LDP messages and eliminates the possibility of source address 1172 spoofing. Use of the MD5 option does not provide privacy, but 1173 privacy of the LDP control messages is not usually considered 1174 important. As the MD5 option relies on the configuration of pre- 1175 shared keys, it does not provide much protection against replay 1176 attacks. In addition, its reliance on pre-shared keys may make it 1177 very difficult to deploy when the set of eligible neighbors is 1178 determined by an auto-configuration protocol. 1180 When the Generalized PWid FEC Element is used, it is possible that a 1181 particular LDP peer may be one of the eligible LDP peers but may not 1182 be the right one to connect to the particular attachment circuit 1183 identified by the particular instance of the Generalized PWid FEC 1184 element. However, given that the peer is known to be one of the 1185 eligible peers (as discussed above), this would be the result of a 1186 configuration error, rather than a security problem. Nevertheless, 1187 it may be advisable for a PE to associate each of its local 1188 attachment circuits with a set of eligible peers rather than have 1189 just a single set of eligible peers associated with the PE as a 1190 whole. 1192 9. Changes from RFC4447 1194 The changes in this document are mostly minor fixes to spelling and 1195 grammar, or clarifications to the text, which were either noted as 1196 errata to RFC4447 or found by the editors. 1198 However a new section (6.3) on control-word renegotiation by label 1199 request message has been added, referencing RFC 6723. The diagram 1200 of C-bit handling procedures has also been removed, as the updated 1201 diagram in RFC 6723 is now definitive. 1203 10. Acknowledgments 1205 The authors wish to acknowledge the contributions of Vach Kompella, 1206 Vanson Lim, Wei Luo, Himanshu Shah, and Nick Weeds. 1208 11. Normative References 1210 [RFC2119] Bradner S., "Key words for use in RFCs to Indicate 1211 Requirement Levels", RFC 2119, March 1997 1213 [RFC5036] "LDP Specification." L. Andersson, P. Ed. 1214 Minei, I. Ed. B. Thomas. January 2001. RFC5036 1216 [RFC3032] "MPLS Label Stack Encoding", E. Rosen, Y. Rekhter, 1217 D. Tappan, G. Fedorkow, D. Farinacci, T. Li, A. Conta. 1218 RFC3032 1220 [RFC4446] "IANA Allocations for pseudo Wire Edge to Edge Emulation 1221 (PWE3)" L. Martini RFC4446 , April 2006 1223 [RFC7358] "Label Advertisement Discipline for LDP Forwarding 1224 Equivalence Classes (FECs)", K. Raza, S. Boutros, L. Martini, 1225 RFC7358, October 2014 1227 12. Informative References 1229 [RFC4842] "Synchronous Optical Network/Synchronous Digital Hierarchy 1230 (SONET/SDH) Circuit Emulation over Packet (CEP)", A. Malis, 1231 P. Pate, R. Cohen, Ed., D. Zelig, RFC4842, April 2007 1233 [RFC4553] "Structure-Agnostic Time Division Multiplexing (TDM) over 1234 Packet (SAToP)", Vainshtein A. Ed. Stein, Ed. YJ. RFC4553, 1235 June 2006 1237 [RFC4619] "Encapsulation Methods for Transport of Frame Relay over 1238 Multiprotocol Label Switching (MPLS) Networks", Martini L. Ed. 1239 C. Kawa Ed. A. Malis Ed. RFC4619, September 2006 1241 [RFC4717] "Encapsulation Methods for Transport of Asynchronous 1242 Transfer Mode (ATM) over MPLS Networks", Martini L. Jayakumar J. 1243 Bocci M. El-Aawar N. Brayley J. Koleyni G. RFC4717, 1244 December 2006 1246 [RFC4618] "Encapsulation Methods for Transport of PPP/High-Level 1247 Data Link Control (HDLC) Frames over MPLS Networks", Martini L. 1248 Rosen E. Heron G. Malis A. RFC4618, September 2006 1250 [RFC4448] "Encapsulation Methods for Transport of Ethernet over 1251 MPLS Networks", Martini L. Ed. Rosen E. El-Aawar N. Heron G. 1252 RFC4448, April 2006. 1254 [RFC4447] "Pseudowire Setup and Maintenance Using the Label 1255 Distribution Protocol (LDP)", Martini L. Ed. Rosen E. 1256 El-Aawar N. Smith T. Heron G. RFC4447, April 2006 1258 [ANSI] American National Standards Institute, "Synchronous Optical 1259 Network Formats," ANSI T1.105-1995. 1261 [ITUG] ITU Recommendation G.707, "Network Node Interface For The 1262 Synchronous Digital Hierarchy", 1996. 1264 [RFC3985] "PWE3 Architecture" Bryant, et al., RFC3985. 1266 [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and 1267 Languages", BCP 18, RFC 2277, January 1998. 1269 13. Author Information 1271 Luca Martini 1272 Cisco Systems, Inc. 1273 9155 East Nichols Avenue, Suite 400 1274 Englewood, CO, 80112 1275 e-mail: lmartini@cisco.com 1276 Giles Heron 1277 Cisco Systems 1278 10 New Square 1279 Bedfont Lakes 1280 Feltham 1281 Middlesex 1282 TW14 8HA 1283 UK 1284 e-mail: giheron@cisco.com 1286 14. Additional Historical Contributing Authors 1288 Nasser El-Aawar 1289 Level 3 Communications, LLC. 1290 1025 Eldorado Blvd. 1291 Broomfield, CO, 80021 1292 e-mail: nna@level3.net 1294 Eric C. Rosen 1295 Cisco Systems, Inc. 1296 1414 Massachusetts Avenue 1297 Boxborough, MA 01719 1298 e-mail: erosen@cisco.com 1300 Dan Tappan 1301 Cisco Systems, Inc. 1302 1414 Massachusetts Avenue 1303 Boxborough, MA 01719 1304 e-mail: tappan@cisco.com 1306 Toby Smith 1307 Google 1308 6425 Penn Ave. #700 1309 Pittsburgh, PA 15206 1310 e-mail: tob@google.com 1312 Dimitri Vlachos 1313 Riverbed Technology 1314 e-mail: dimitri@riverbed.com 1315 Jayakumar Jayakumar, 1316 Cisco Systems Inc. 1317 3800 Zanker Road, MS-SJ02/2, 1318 San Jose, CA, 95134 1319 e-mail: jjayakum@cisco.com 1321 Alex Hamilton, 1322 Cisco Systems Inc. 1323 485 East Tasman Drive, MS-SJC07/3, 1324 San Jose, CA, 95134 1325 e-mail: tahamilt@cisco.com 1327 Steve Vogelsang 1328 ECI Telecom 1329 Omega Corporate Center 1330 1300 Omega Drive 1331 Pittsburgh, PA 15205 1332 e-mail: stephen.vogelsang@ecitele.com 1334 John Shirron 1335 ECI Telecom 1336 Omega Corporate Center 1337 1300 Omega Drive 1338 Pittsburgh, PA 15205 1339 e-mail: john.shirron@ecitele.com 1341 Andrew G. 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