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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 Obsoletes: 4447, 6723 (if approved) 5 Intended status: Standards Track Cisco 6 Expires: March 15, 2016 8 September 15, 2015 10 Pseudowire Setup and Maintenance using the Label Distribution Protocol 12 draft-ietf-pals-rfc4447bis-02.txt 14 Status of this Memo 16 This Internet-Draft is submitted to IETF in full conformance with the 17 provisions of BCP 78 and 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 March 15, 2015 37 Abstract 39 Layer 2 services (such as Frame Relay, Asynchronous Transfer Mode, 40 and Ethernet) can be "emulated" over an MPLS backbone by 41 encapsulating the Layer 2 Protocol Data Units (PDU) and then 42 transmitting them over "pseudowires". It is also possible to use 43 pseudowires to provide low-rate Time Division Multiplexed and 44 Synchronous Optical NETworking circuit emulation over an MPLS-enabled 45 network. This document specifies a protocol for establishing and 46 maintaining the pseudowires, using extensions to the Label 47 Distribution Protocol (LDP). Procedures for encapsulating Layer 2 48 PDUs are specified in a set of companion documents. 50 This document has been written to address errata in a previous 51 version of this standard. 53 Table of Contents 55 1 Changes from RFC4447 ................................. 4 56 2 Introduction ......................................... 4 57 3 Specification of Requirements ........................ 7 58 4 The Pseudowire Label ................................. 7 59 5 Details Specific to Particular Emulated Services ..... 9 60 5.1 IP Layer 2 Transport ................................. 9 61 6 LDP .................................................. 9 62 6.1 The PWid FEC Element ................................. 10 63 6.2 The Generalized PWid FEC Element ..................... 11 64 6.2.1 Attachment Identifiers ............................... 12 65 6.2.2 Encoding the Generalized PWid FEC Element ............ 13 66 6.2.2.1 Interface Parameters TLV ............................. 15 67 6.2.2.2 PW Grouping ID TLV ................................... 15 68 6.2.3 Signaling Procedures ................................. 16 69 6.3 Signaling of Pseudowire Status ....................... 17 70 6.3.1 Use of Label Mapping Messages ........................ 17 71 6.3.2 Signaling PW Status .................................. 17 72 6.3.3 Pseudowire Status Negotiation Procedures ............. 19 73 6.4 Interface Parameters Sub-TLV ......................... 21 74 6.5 LDP label Withdrawal procedures ...................... 22 75 7 Control Word ......................................... 22 76 7.1 PW Types for which the Control Word is REQUIRED ...... 22 77 7.2 PW Types for which the Control Word is NOT mandatory . 22 78 7.3 Control-Word Renegotiation by Label Request Message .. 24 79 7.4 Sequencing Considerations ............................ 25 80 7.4.1 Label Advertisements ................................. 25 81 7.4.2 Label Release ........................................ 25 82 8 IANA Considerations .................................. 26 83 8.1 LDP TLV TYPE ......................................... 26 84 8.2 LDP Status Codes ..................................... 26 85 8.3 FEC Type Name Space .................................. 26 86 9 Security Considerations .............................. 26 87 9.1 Data-Plane Security .................................. 26 88 9.2 Control-Plane Security ............................... 28 89 10 Acknowledgments ...................................... 29 90 11 Normative References ................................. 29 91 12 Informative References ............................... 29 92 13 Author Information ................................... 30 93 14 Additional Historical Contributing Authors ........... 31 95 1. Changes from RFC4447 97 The changes in this document are mostly minor fixes to spelling and 98 grammar, or clarifications to the text, which were either noted as 99 errata to RFC4447 or found by the editors. 101 However a new section (6.3) on control-word renegotiation by label 102 request message has been added, obsoleting RFC 6723. The diagram of 103 C-bit handling procedures has also been removed. A note was added to 104 clarify that the C-bit is part of the FEC. 106 2. Introduction 108 [RFC4619], [RFC4717], [RFC4618], and [RFC4448] explain how to 109 encapsulate a Layer 2 Protocol Data Unit (PDU) for transmission over 110 an MPLS-enabled network. Those documents specify that a "pseudowire 111 header", consisting of a demultiplexor field, will be prepended to 112 the encapsulated PDU. The pseudowire demultiplexor field is 113 prepended before transmitting a packet on a pseudowire. When the 114 packet arrives at the remote endpoint of the pseudowire, the 115 demultiplexor is what enables the receiver to identify the particular 116 pseudowire on which the packet has arrived. To transmit the packet 117 from one pseudowire endpoint to another, the packet may need to 118 travel through a "Packet Switched Network (PSN) tunnel"; this will 119 require that an additional header be prepended to the packet. 121 Accompanying documents [RFC4842], [RFC4553] specify methods for 122 transporting time-division multiplexing (TDM) digital signals (TDM 123 circuit emulation) over a packet-oriented MPLS-enabled network. The 124 transmission system for circuit-oriented TDM signals is the 125 Synchronous Optical Network [ANSI] (SONET)/Synchronous Digital 126 Hierarchy (SDH) [ITUG]. To support TDM traffic, which includes 127 voice, data, and private leased-line service, the pseudowires must 128 emulate the circuit characteristics of SONET/SDH payloads. The TDM 129 signals and payloads are encapsulated for transmission over 130 pseudowires. A pseudowire demultiplexor and a PSN tunnel header is 131 prepended to this encapsulation. 133 [RFC4553] describes methods for transporting low-rate time-division 134 multiplexing (TDM) digital signals (TDM circuit emulation) over PSNs, 135 while [RFC4842] similarly describes transport of high-rate TDM 136 (SONET/SDH). To support TDM traffic, the pseudowires must emulate 137 the circuit characteristics of the original T1, E1, T3, E3, SONET, or 138 SDH signals. [RFC4553] does this by encapsulating an arbitrary but 139 constant amount of the TDM data in each packet, and the other methods 140 encapsulate TDM structures. 142 In this document, we specify the use of the MPLS Label Distribution 143 Protocol, LDP [RFC5036], as a protocol for setting up and maintaining 144 the pseudowires. In particular, we define new TLVs, FEC elements, 145 parameters, and codes for LDP, which enable LDP to identify 146 pseudowires and to signal attributes of pseudowires. We specify how 147 a pseudowire endpoint uses these TLVs in LDP to bind a demultiplexor 148 field value to a pseudowire, and how it informs the remote endpoint 149 of the binding. We also specify procedures for reporting pseudowire 150 status changes, for passing additional information about the 151 pseudowire as needed, and for releasing the bindings. These 152 procedures are intended to be independent of the underlying version 153 of IP used for LDP signaling. 155 In the protocol specified herein, the pseudowire demultiplexor field 156 is an MPLS label. Thus, the packets that are transmitted from one 157 end of the pseudowire to the other are MPLS packets, which must be 158 transmitted through an MPLS tunnel. However, if the pseudowire 159 endpoints are immediately adjacent and penultimate hop popping 160 behavior is in use, the MPLS tunnel may not be necessary. Any sort 161 of PSN tunnel can be used, as long as it is possible to transmit MPLS 162 packets through it. The PSN tunnel can itself be an MPLS LSP, or any 163 other sort of tunnel that can carry MPLS packets. Procedures for 164 setting up and maintaining the MPLS tunnels are outside the scope of 165 this document. 167 This document deals only with the setup and maintenance of point-to- 168 point pseudowires. Neither point-to-multipoint nor multipoint-to- 169 point pseudowires are discussed. 171 QoS-related issues are not discussed in this document. 173 The following two figures describe the reference models that are 174 derived from [RFC3985] to support the PW emulated services. 176 |<-------------- Emulated Service ---------------->| 177 | | 178 | |<------- Pseudowire ------->| | 179 | | | | 180 |Attachment| |<-- PSN Tunnel -->| |Attachment| 181 | Circuit V V V V Circuit | 182 V (AC) +----+ +----+ (AC) V 183 +-----+ | | PE1|==================| PE2| | +-----+ 184 | |----------|............PW1.............|----------| | 185 | CE1 | | | | | | | | CE2 | 186 | |----------|............PW2.............|----------| | 187 +-----+ ^ | | |==================| | | ^ +-----+ 188 ^ | +----+ +----+ | | ^ 189 | | Provider Edge 1 Provider Edge 2 | | 190 | | | | 191 Customer | | Customer 192 Edge 1 | | Edge 2 193 | | 194 native service native service 196 Figure 1: PWE3 Reference Model 198 +-----------------+ +-----------------+ 199 |Emulated Service | |Emulated Service | 200 |(e.g., TDM, ATM) |<==== Emulated Service ===>|(e.g., TDM, ATM) | 201 +-----------------+ +-----------------+ 202 | Payload | | Payload | 203 | Encapsulation |<====== Pseudowire =======>| Encapsulation | 204 +-----------------+ +-----------------+ 205 |PW Demultiplexer | |PW Demultiplexer | 206 | PSN Tunnel, |<======= PSN Tunnel ======>| PSN Tunnel, | 207 | PSN & Physical | | PSN & Physical | 208 | Layers | | Layers | 209 +-------+---------+ ___________ +---------+-------+ 210 | / | 211 +===============/ PSN ===============+ 212 / 213 _____________/ 215 Figure 2: PWE3 Protocol Stack Reference Model 217 For the purpose of this document, PE1 will be defined as the ingress 218 router, and PE2 as the egress router. A layer 2 PDU will be received 219 at PE1, encapsulated at PE1, transported and decapsulated at PE2, and 220 transmitted out of PE2. 222 Note that this document was written to address errata in [RFC4447]. 224 3. Specification of Requirements 226 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 227 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 228 document are to be interpreted as described in [RFC2119]. 230 4. The Pseudowire Label 232 Suppose that it is desired to transport Layer 2 PDUs from ingress LSR 233 PE1 to egress LSR PE2, across an intervening MPLS-enabled network. 234 We assume that there is an MPLS tunnel from PE1 to PE2. That is, we 235 assume that PE1 can cause a packet to be delivered to PE2 by 236 encapsulating the packet in an "MPLS tunnel header" and sending the 237 result to one of its adjacencies. The MPLS tunnel is an MPLS Label 238 Switched Path (LSP); thus, putting on an MPLS tunnel encapsulation is 239 a matter of pushing on an MPLS label. 241 We presuppose that a large number of pseudowires can be carried 242 through a single MPLS tunnel. Thus it is never necessary to maintain 243 state in the network core for individual pseudowires. We do not 244 presuppose that the MPLS tunnels are point to point; although the 245 pseudowires are point to point, the MPLS tunnels may be multipoint to 246 point. We do not presuppose that PE2 will even be able to determine 247 the MPLS tunnel through which a received packet was transmitted. 248 (For example, if the MPLS tunnel is an LSP and penultimate hop 249 popping is used, when the packet arrives at PE2, it will contain no 250 information identifying the tunnel.) 252 When PE2 receives a packet over a pseudowire, it must be able to 253 determine that the packet was in fact received over a pseudowire, and 254 it must be able to associate that packet with a particular 255 pseudowire. PE2 is able to do this by examining the MPLS label that 256 serves as the pseudowire demultiplexor field shown in Figure 2. Call 257 this label the "PW label". 259 When PE1 sends a Layer 2 PDU to PE2, it creates an MPLS packet by 260 adding the PW label to the packet, thus creating the first entry of 261 the label stack. If the PSN tunnel is an MPLS LSP, the PE1 pushes 262 another label (the tunnel label) onto the packet as the second entry 263 of the label stack. The PW label is not visible again until the MPLS 264 packet reaches PE2. PE2's disposition of the packet is based on the 265 PW label. 267 If the payload of the MPLS packet is, for example, an ATM AAL5 PDU, 268 the PW label will generally correspond to a particular ATM VC at PE2. 269 That is, PE2 needs to be able to infer from the PW label the outgoing 270 interface and the VPI/VCI value for the AAL5 PDU. If the payload is 271 a Frame Relay PDU, then PE2 needs to be able to infer from the PW 272 label the outgoing interface and the DLCI value. If the payload is 273 an Ethernet frame, then PE2 needs to be able to infer from the PW 274 label the outgoing interface, and perhaps the VLAN identifier. This 275 process is uni-directional and will be repeated independently for 276 bi-directional operation. When using the PWid FEC Element, it is 277 REQUIRED that the same PW ID and PW type be assigned for a given 278 circuit in both directions. The group ID (see below) MUST NOT be 279 required to match in both directions. The transported frame MAY be 280 modified when it reaches the egress router. If the header of the 281 transported Layer 2 frame is modified, this MUST be done at the 282 egress LSR only. Note that the PW label must always be at the bottom 283 of the packet's label stack, and labels MUST be allocated from the 284 per-platform label space. 286 This document does not specify a method for distributing the MPLS 287 tunnel label or any other labels that may appear above the PW label 288 on the stack. Any acceptable method of MPLS label distribution will 289 do. This document specifies a protocol for assigning and distributing 290 the PW label. This protocol is LDP, extended as specified in the 291 remainder of this document. An LDP session must be set up between the 292 pseudowire endpoints. LDP MUST exchange PW FEC label bindings in 293 downstream unsolicited mode, independent of the negotiated label 294 advertisement mode of the LDP session according to the specifications 295 in specified in [RFC7358]. LDP's "liberal label retention" mode 296 SHOULD be used. However all the LDP procedures that are specified in 297 [RFC5036], and that are also applicable to this protocol 298 specification MUST be implemented. 300 This document requires that a receiving LSR MUST respond to a Label 301 Request message with either a Label Mapping for the requested label 302 or with a Notification message that indicates why it cannot satisfy 303 the request. These procedures are specified in [RFC5036] section 304 3.5.7 "Label Mapping Message", and 3.5.8 "Label Request Message". 305 Note that sending these responses is a stricter requirement than is 306 specified in RFC5036, but these response messages are REQUIRED to 307 ensure correct operation of this protocol. 309 In addition to the protocol specified herein, static assignment of PW 310 labels may be used, and implementations of this protocol SHOULD 311 provide support for static assignment. PW encapsulation is always 312 symmetrical in both directions of traffic along a specific PW, 313 whether the PW uses an LDP control plane or not. 315 This document specifies all the procedures necessary to set up and 316 maintain the pseudowires needed to support "unswitched" point to 317 point services, where each endpoint of the pseudowire is provisioned 318 with the identity of the other endpoint. There are also protocol 319 mechanisms specified herein that can be used to support switched 320 services and other provisioning models. However, the use of the 321 protocol mechanisms to support those other models and services is not 322 described in this document. 324 5. Details Specific to Particular Emulated Services 326 5.1. IP Layer 2 Transport 328 This mode carries IP packets over a pseudowire. The encapsulation 329 used is according to [RFC3032]. The PW control word MAY be inserted 330 between the MPLS label stack and the IP payload. The encapsulation 331 of the IP packets for forwarding on the attachment circuit is 332 implementation specific, is part of the native service processing 333 (NSP) function [RFC3985], and is outside the scope of this document. 335 6. LDP 337 The PW label bindings are distributed using the LDP downstream 338 unsolicited mode described in [RFC5036]. The PEs will establish an 339 LDP session using the Extended Discovery mechanism described in [LDP, 340 sectionn 2.4.2 and 2.5]. 342 An LDP Label Mapping message contains an FEC TLV, a Label TLV, and 343 zero or more optional parameter TLVs. 345 The FEC TLV is used to indicate the meaning of the label. In the 346 current context, the FEC TLV would be used to identify the particular 347 pseudowire that a particular label is bound to. In this 348 specification, we define two new FEC TLVs to be used for identifying 349 pseudowires. When setting up a particular pseudowire, only one of 350 these FEC TLVs is used. The one to be used will depend on the 351 particular service being emulated and on the particular provisioning 352 model being supported. 354 LDP allows each FEC TLV to consist of a set of FEC elements. For 355 setting up and maintaining pseudowires, however, each FEC TLV MUST 356 contain exactly one FEC element. 358 The LDP base specification has several kinds of label TLVs, including 359 the Generic Label TLV, as specified in [RFC5036], section 3.4.2.1. 360 For setting up and maintaining pseudowires, the Generic Label TLV 361 MUST be used. 363 6.1. The PWid FEC Element 365 The PWid FEC element may be used whenever both pseudowire endpoints 366 have been provisioned with the same 32-bit identifier for the 367 pseudowire. 369 For this purpose, a new type of FEC element is defined. The FEC 370 element type is 0x80 and is defined as follows: 372 0 1 2 3 373 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 1 374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 375 | PWid (0x80) |C| PW type |PW info Length | 376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 377 | Group ID | 378 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 379 | PW ID | 380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 381 | Interface Parameter Sub-TLV | 382 | " | 383 | " | 384 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 386 - PW type 388 A 15 bit quantity containing a value that represents the type of 389 PW. Assigned Values are specified in "IANA Allocations for 390 pseudo Wire Edge to Edge Emulation (PWE3)" [RFC4446]. 392 - Control word bit (C) 394 The bit (C) is used to flag the presence of a control word as 395 follows: 397 C = 1 control word present on this PW. 398 C = 0 no control word present on this PW. 400 Please see the section "Control Word" for further explanation. 402 - PW information length 404 Length of the PW ID field and the interface parameters sub-TLV in 405 octets. If this value is 0, then it references all PWs using the 406 specified group ID, and there is no PW ID present, nor are there 407 any interface parameter sub-TLVs. 409 - Group ID 411 An arbitrary 32 bit value which represents a group of PWs that is 412 used to create groups in the PW space. The group ID is intended 413 to be used as a port index, or a virtual tunnel index. To 414 simplify configuration a particular PW ID at ingress could be 415 part of a Group ID assigned to the virtual tunnel for transport 416 to the egress router. The Group ID is very useful for sending 417 wild card label withdrawals, or PW wild card status notification 418 messages to remote PEs upon physical port failure. 420 - PW ID 422 A non-zero 32-bit connection ID that together with the PW type 423 identifies a particular PW. Note that the PW ID and the PW type 424 MUST be the same at both endpoints. 426 - Interface Parameter Sub-TLV 428 This variable length TLV is used to provide interface specific 429 parameters, such as attachment circuit MTU. 431 Note that as the "interface parameter sub-TLV" is part of the 432 FEC, the rules of LDP make it impossible to change the interface 433 parameters once the pseudowire has been set up. Thus the 434 interface parameters field must not be used to pass information, 435 such as status information, that may change during the life of 436 the pseudowire. Optional parameter TLVs should be used for that 437 purpose. 439 Using the PWid FEC, each of the two pseudowire endpoints 440 independently initiates the setup of a unidirectional LSP. An 441 outgoing LSP and an incoming LSP are bound together into a single 442 pseudowire if they have the same PW ID and PW type. 444 6.2. The Generalized PWid FEC Element 446 The PWid FEC element can be used if a unique 32-bit value has been 447 assigned to the PW, and if each endpoint has been provisioned with 448 that value. The Generalized PWid FEC element requires that the PW 449 endpoints be uniquely identified; the PW itself is identified as a 450 pair of endpoints. In addition, the endpoint identifiers are 451 structured to support applications where the identity of the remote 452 endpoints needs to be auto-discovered rather than statically 453 configured. 455 The "Generalized PWid FEC Element" is FEC type 0x81. 457 The Generalized PWid FEC Element does not contain anything 458 corresponding to the "Group ID" of the PWid FEC element. The 459 functionality of the "Group ID" is provided by a separate optional 460 LDP TLV, the "PW Grouping TLV", described below. The Interface 461 Parameters field of the PWid FEC element is also absent; its 462 functionality is replaced by the optional Interface Parameters TLV, 463 described below. 465 6.2.1. Attachment Identifiers 467 As discussed in [RFC3985], a pseudowire can be thought of as 468 connecting two "forwarders". The protocol used to set up a 469 pseudowire must allow the forwarder at one end of a pseudowire to 470 identify the forwarder at the other end. We use the term "attachment 471 identifier", or "AI", to refer to the field that the protocol uses to 472 identify the forwarders. In the PWid FEC, the PWid field serves as 473 the AI. In this section, we specify a more general form of AI that 474 is structured and of variable length. 476 Every Forwarder in a PE must be associated with an Attachment 477 Identifier (AI), either through configuration or through some 478 algorithm. The Attachment Identifier must be unique in the context 479 of the PE router in which the Forwarder resides. The combination must be globally unique. 482 It is frequently convenient to regard a set of Forwarders as being 483 members of a particular "group", where PWs may only be set up among 484 members of a group. In such cases, it is convenient to identify the 485 Forwarders relative to the group, so that an Attachment Identifier 486 would consist of an Attachment Group Identifier (AGI) plus an 487 Attachment Individual Identifier (AII). 489 An Attachment Group Identifier may be thought of as a VPN-id, or a 490 VLAN identifier, some attribute that is shared by all the Attachment 491 PWs (or pools thereof) that are allowed to be connected. 493 The details of how to construct the AGI and AII fields identifying 494 the pseudowire endpoints are outside the scope of this specification. 495 Different pseudowire applications, and different provisioning models, 496 will require different sorts of AGI and AII fields. The 497 specification of each such application and/or model must include the 498 rules for constructing the AGI and AII fields. 500 As previously discussed, a (bidirectional) pseudowire consists of a 501 pair of unidirectional LSPs, one in each direction. If a particular 502 pseudowire connects PE1 with PE2, the PW direction from PE1 to PE2 503 can be identified as: 505 , PE2, >, 507 and the PW direction from PE2 to PE1 can be identified by: 509 , PE1, >. 511 Note that the AGI must be the same at both endpoints, but the AII 512 will in general be different at each endpoint. Thus, from the 513 perspective of a particular PE, each pseudowire has a local or 514 "Source AII", and a remote or "Target AII". The pseudowire setup 515 protocol can carry all three of these quantities: 517 - Attachment Group Identifier (AGI). 519 - Source Attachment Individual Identifier (SAII) 521 - Target Attachment Individual Identifier (TAII) 523 If the AGI is non-null, then the Source AI (SAI) consists of the AGI 524 together with the SAII, and the Target AI (TAI) consists of the TAII 525 together with the AGI. If the AGI is null, then the SAII and TAII 526 are the SAI and TAI, respectively. 528 The interpretation of the SAI and TAI is a local matter at the 529 respective endpoint. 531 The association of two unidirectional LSPs into a single 532 bidirectional pseudowire depends on the SAI and the TAI. Each 533 application and/or provisioning model that uses the Generalized PWid 534 FEC element must specify the rules for performing this association. 536 6.2.2. Encoding the Generalized PWid FEC Element 538 FEC element type 0x81 is used. The FEC element is encoded as 539 follows: 541 0 1 2 3 542 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 1 543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 544 |Gen PWid (0x81)|C| PW Type |PW info Length | 545 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 546 | AGI Type | Length | Value | 547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 548 ~ AGI Value (contd.) ~ 549 | | 550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 551 | AII Type | Length | Value | 552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 553 ~ SAII Value (contd.) ~ 554 | | 555 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 556 | AII Type | Length | Value | 557 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 558 ~ TAII Value (contd.) ~ 559 | | 560 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 562 This document does not specify the AII and AGI type field values; 563 specification of the type field values to be used for a particular 564 application is part of the specification of that application. IANA 565 has assigned these values using the method defined in the [RFC4446] 566 document. 568 The SAII, TAII, and AGI are simply carried as octet strings. The 569 length byte specifies the size of the Value field. The null string 570 can be sent by setting the length byte to 0. If a particular 571 application does not need all three of these sub-elements, it MUST 572 send all the sub-elements but set the length to 0 for the unused 573 sub-elements. 575 The PW information length field contains the length of the SAII, 576 TAII, and AGI, combined in octets. If this value is 0, then it 577 references all PWs using the specific grouping ID (specified in the 578 PW grouping ID TLV). In this case, there are no other FEC element 579 fields (AGI, SAII, etc.) present, nor any interface parameters TLVs. 581 Note that the interpretation of a particular field as AGI, SAII, or 582 TAII depends on the order of its occurrence. The type field 583 identifies the type of the AGI, SAII, or TAII. When comparing two 584 occurrences of an AGI (or SAII or TAII), the two occurrences are 585 considered identical if the type, length, and value fields of one are 586 identical, respectively, to those of the other. 588 6.2.2.1. Interface Parameters TLV 590 This TLV MUST only be used when sending the Generalized PW FEC. It 591 specifies interface-specific parameters. Specific parameters, when 592 applicable, MUST be used to validate that the PEs and the ingress and 593 egress ports at the edges of the circuit have the necessary 594 capabilities to interoperate with each other. 596 0 1 2 3 597 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 1 598 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 599 |0|0| PW Intf P. TLV (0x096B) | Length | 600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 601 | Sub-TLV Type | Length | Variable Length Value | 602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 603 | Variable Length Value | 604 | " | 605 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 607 A more detailed description of this field can be found in the section 608 "Interface Parameters Sub-TLV", below. 610 6.2.2.2. PW Grouping ID TLV 612 0 1 2 3 613 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 1 614 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 615 |0|0|PW Grouping ID TLV (0x096C)| Length | 616 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 617 | Value | 618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 620 The PW Grouping ID is an arbitrary 32-bit value that represents an 621 arbitrary group of PWs. It is used to create group PWs; for example, 622 a PW Grouping ID can be used as a port index and assigned to all PWs 623 that lead to that port. Use of the PW Grouping ID enables one to 624 send "wild card" label withdrawals, or "wild card" status 625 notification messages, to remote PEs upon physical port failure. 627 Note Well: The PW Grouping ID is different from and has no relation 628 to, the Attachment Group Identifier. 630 The PW Grouping ID TLV is not part of the FEC and will not be 631 advertised except in the PW FEC advertisement. The advertising PE 632 MAY use the wild card withdraw semantics, but the remote PEs MUST 633 implement support for wild card messages. This TLV MUST only be used 634 when sending the Generalized PW ID FEC. 636 To issue a wild card command (status or withdraw): 638 - Set the PW Info Length to 0 in the Generalized PWid FEC Element. 639 - Send only the PW Grouping ID TLV with the FEC (no AGI/SAII/TAII 640 is sent). 642 6.2.3. Signaling Procedures 644 In order for PE1 to begin signaling PE2, PE1 must know the address of 645 the remote PE2, and a TAI. This information may have been configured 646 at PE1, or it may have been learned dynamically via some 647 autodiscovery procedure. 649 The egress PE (PE1), which has knowledge of the ingress PE, initiates 650 the setup by sending a Label Mapping Message to the ingress PE (PE2). 651 The Label Mapping message contains the FEC TLV, carrying the 652 Generalized PWid FEC Element (type 0x81). The Generalized PWid FEC 653 element contains the AGI, SAII, and TAII information. 655 Next, when PE2 receives such a Label Mapping message, PE2 interprets 656 the message as a request to set up a PW whose endpoint (at PE2) is 657 the Forwarder identified by the TAI. From the perspective of the 658 signaling protocol, exactly how PE2 maps AIs to Forwarders is a local 659 matter. In some Virtual Private Wire Services (VPWS) provisioning 660 models, the TAI might, for example, be a string that identifies a 661 particular Attachment Circuit, such as "ATM3VPI4VCI5", or it might, 662 for example, be a string, such as "Fred", that is associated by 663 configuration with a particular Attachment Circuit. In VPLS, the AGI 664 could be a VPN-id, identifying a particular VPLS instance. 666 If PE2 cannot map the TAI to one of its Forwarders, then PE2 sends a 667 Label Release message to PE1, with a Status Code of 668 "Unassigned/Unrecognized TAI", and the processing of the Label 669 Mapping message is complete. 671 The FEC TLV sent in a Label Release message is the same as the FEC 672 TLV received in the Label Mapping being released (but without the 673 interface parameter TLV). More generally, the FEC TLV is the same in 674 all LDP messages relating to the same PW. In a Label Release this 675 means that the SAII is the remote peer's AII and the TAII is the 676 sender's local AII. 678 If the Label Mapping Message has a valid TAI, PE2 must decide whether 679 to accept it. The procedures for so deciding will depend on the 680 particular type of Forwarder identified by the TAI. Of course, the 681 Label Mapping message may be rejected due to standard LDP error 682 conditions as detailed in [RFC5036]. 684 If PE2 decides to accept the Label Mapping message, then it has to 685 make sure that a PW LSP is set up in the opposite (PE1-->PE2) 686 direction. If it has already signaled for the corresponding PW LSP 687 in that direction, nothing more needs to be done. Otherwise, it must 688 initiate such signaling by sending a Label Mapping message to PE1. 689 This is very similar to the Label Mapping message PE2 received, but 690 the SAI and TAI are reversed. 692 Thus, a bidirectional PW consists of two LSPs, where the FEC of one 693 has the SAII and TAII reversed with respect to the FEC of the other. 695 6.3. Signaling of Pseudowire Status 697 6.3.1. Use of Label Mapping Messages 699 The PEs MUST send Label Mapping Messages to their peers as soon as 700 the PW is configured and administratively enabled, regardless of the 701 attachment circuit state. The PW label should not be withdrawn 702 unless the operator administratively configures the pseudowire down 703 (or the PW configuration is deleted entirely). Using the procedures 704 outlined in this section, a simple label withdraw method MAY also be 705 supported as a legacy means of signaling PW status and AC status. In 706 any case, if the label-to-PW binding is not available the PW MUST be 707 considered in the down state. 709 Once the PW status negotiation procedures are completed and if they 710 result in the use of the label withdraw method for PW status 711 communication, and this method is not supported by one of the PEs, 712 then that PE must send a Label Release Message to its peer with the 713 following error: 715 "Label Withdraw PW Status Method Not Supported" 717 If the label withdraw method for PW status communication is selected 718 for the PW, it will result in the Label Mapping Message being 719 advertised only if the attachment circuit is active. The PW status 720 signaling procedures described in this section MUST be fully 721 implemented. 723 6.3.2. Signaling PW Status 725 The PE devices use an LDP TLV to indicate status to their remote 726 peers. This PW Status TLV contains more information than the 727 alternative simple Label Withdraw message. 729 The format of the PW Status TLV is: 731 0 1 2 3 732 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 1 733 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 734 |1|0| PW Status (0x096A) | Length | 735 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 736 | Status Code | 737 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 739 The status code is a 4 octet bit field as specified in the PW IANA 740 Allocations document [RFC4446]. The length specifies the length of 741 the Status Code field in octets (equal to 4). 743 Each bit in the status code field can be set individually to indicate 744 more than a single failure at once. Each fault can be cleared by 745 sending an appropriate Notification message in which the respective 746 bit is cleared. The presence of the lowest bit (PW Not Forwarding) 747 acts only as a generic failure indication when there is a link-down 748 event for which none of the other bits apply. 750 The Status TLV is transported to the remote PW peer via the LDP 751 Notification message. The general format of the Notification Message 752 is: 754 0 1 2 3 755 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 1 756 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 757 |0| Notification (0x0001) | Message Length | 758 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 759 | Message ID | 760 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 761 | Status (TLV) | 762 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 763 | PW Status TLV | 764 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 765 | PWId FEC TLV or Generalized ID FEC TLV | 766 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 767 | PW Grouping ID TLV (Optional) | 768 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 770 The Status TLV status code is set to 0x00000028, "PW status", to 771 indicate that PW status follows. Since this notification does not 772 refer to any particular message, the Message Id and Message Type 773 fields are set to 0. 775 The PW FEC TLV SHOULD NOT include the interface parameter sub-TLVs, 776 as they are ignored in the context of this message. However the PW 777 FEC TLV MUST include the C bit, where aplicable, as it is part of the 778 FEC. When a PE's attachment circuit encounters an error, use of the 779 PW Notification Message allows the PE to send a single "wild card" 780 status message, using a PW FEC TLV with only the group ID set, to 781 denote this change in status for all affected PW connections. This 782 status message contains either the PW FEC TLV with only the group ID 783 set, or else it contains the Generalized FEC TLV with only the PW 784 Grouping ID TLV. 786 As mentioned above, the Group ID field of the PWid FEC element, or 787 the PW Grouping ID TLV used with the Generalized PWid FEC element, 788 can be used to send a status notification for all arbitrary sets of 789 PWs. This procedure is OPTIONAL, and if it is implemented, the LDP 790 Notification message should be as follows: If the PWid FEC element is 791 used, the PW information length field is set to 0, the PW ID field is 792 not present, and the interface parameter sub-TLVs are not present. 793 If the Generalized FEC element is used, the AGI, SAII, and TAII are 794 not present, the PW information length field is set to 0, the PW 795 Grouping ID TLV is included, and the Interface Parameters TLV is 796 omitted. For the purpose of this document, this is called the "wild 797 card PW status notification procedure", and all PEs implementing this 798 design are REQUIRED to accept such a notification message but are not 799 required to send it. 801 6.3.3. Pseudowire Status Negotiation Procedures 803 When a PW is first set up, the PEs MUST attempt to negotiate the 804 usage of the PW status TLV. This is accomplished as follows: A PE 805 that supports the PW Status TLV MUST include it in the initial Label 806 Mapping message following the PW FEC and the interface parameter 807 sub-TLVs. The PW Status TLV will then be used for the lifetime of 808 the pseudowire. This is shown in the following diagram: 810 0 1 2 3 811 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 1 812 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 813 | | 814 + PWId FEC or Generalized ID FEC + 815 | | 816 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 817 | Interface Parameters | 818 | " | 819 | " | 820 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 821 |0|0| Generic Label (0x0200) | Length | 822 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 823 | Label | 824 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 825 |1|0| PW Status (0x096A) | Length | 826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 827 | Status Code | 828 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 830 If a PW Status TLV is included in the initial Label Mapping message 831 for a PW, then if the Label Mapping message from the remote PE for 832 that PW does not include a PW status TLV, or if the remote PE does 833 not support the PW Status TLV, the PW will revert to the label 834 withdraw method of signaling PW status. Note that if the PW Status 835 TLV is not supported by the remote peer, the peer will automatically 836 ignore it, since the I (ignore) bit is set in the TLV. The PW Status 837 TLV, therefore, will not be present in the corresponding FEC 838 advertisement from the remote LDP peer, which results in exactly the 839 above behavior. 841 If the PW Status TLV is not present following the FEC TLV in the 842 initial PW Label Mapping message received by a PE, then the PW Status 843 TLV will not be used, and both PEs supporting the pseudowire will 844 revert to the label withdraw procedure for signaling status changes. 846 If the negotiation process results in the usage of the PW status TLV, 847 then the actual PW status is determined by the PW status TLV that was 848 sent within the initial PW Label Mapping message. Subsequent updates 849 of PW status are conveyed through the notification message. 851 6.4. Interface Parameters Sub-TLV 853 This field specifies interface-specific parameters. When applicable, 854 it MUST be used to validate that the PEs and the ingress and egress 855 ports at the edges of the circuit have the necessary capabilities to 856 interoperate with each other. The field structure is defined as 857 follows: 859 0 1 2 3 860 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 1 861 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 862 | Sub-TLV Type | Length | Variable Length Value | 863 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 864 | Variable Length Value | 865 | " | 866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 868 The interface parameter sub-TLV type values are specified in "IANA 869 Allocations for Pseudowire Edge to Edge Emulation (PWE3)" [RFC4446]. 871 The Length field is defined as the length of the interface parameter 872 including the parameter id and length field itself. Processing of 873 the interface parameters should continue when unknown interface 874 parameters are encountered, and they MUST be silently ignored. 876 - Interface MTU sub-TLV type 878 A 2 octet value indicating the MTU in octets. This is the 879 Maximum Transmission Unit, excluding encapsulation overhead, of 880 the egress packet interface that will be transmitting the 881 decapsulated PDU that is received from the MPLS-enabled network. 882 This parameter is applicable only to PWs transporting packets and 883 is REQUIRED for these PW types. If this parameter does not match 884 in both directions of a specific PW, that PW MUST NOT be enabled. 886 - Optional Interface Description string sub-TLV type 888 This arbitrary, and OPTIONAL, interface description string is 889 used to send a human-readable administrative string describing 890 the interface to the remote. This parameter is OPTIONAL, and is 891 applicable to all PW types. The interface description parameter 892 string length is variable, and can be from 0 to 80 octets. 893 Human-readable text MUST be provided in the UTF-8 charset using 894 the Default Language [RFC2277]. 896 6.5. LDP label Withdrawal procedures 898 As mentioned above, the Group ID field of the PWid FEC element, or 899 the PW Grouping ID TLV used with the Generalized PWid FEC element, 900 can be used to withdraw all PW labels associated with a particular PW 901 group. This procedure is OPTIONAL, and if it is implemented, the LDP 902 Label Withdraw message should be as follows: If the PWid FEC element 903 is used, the PW information length field is set to 0, the PW ID field 904 is not present, the interface parameter sub-TLVs are not present, and 905 the Label TLV is not present. If the Generalized FEC element is 906 used, the AGI, SAII, and TAII are not present, the PW information 907 length field is set to 0, the PW Grouping ID TLV is included, the 908 Interface Parameters TLV is not present, and the Label TLV is not 909 present. For the purpose of this document, this is called the "wild 910 card withdraw procedure", and all PEs implementing this design are 911 REQUIRED to accept such withdrawn message but are not required to 912 send it. Note that the PW Grouping ID TLV only applies to PWs using 913 the Generalized ID FEC element, while the Group ID only applies to 914 PWid FEC element. 916 The interface parameter sub-TLVs, or TLV, MUST NOT be present in any 917 LDP PW Label Withdraw or Label Release message. A wild card Label 918 Release message MUST include only the group ID, or Grouping ID TLV. 919 A Label Release message initiated by a PE router must always include 920 the PW ID. 922 7. Control Word 924 7.1. PW Types for which the Control Word is REQUIRED 926 The Label Mapping messages that are sent in order to set up these PWs 927 MUST have c=1. When a Label Mapping message for a PW of one of these 928 types is received and c=0, a Label Release message MUST be sent, with 929 an "Illegal C-bit" status code. In this case, the PW will not be 930 enabled. 932 7.2. PW Types for which the Control Word is NOT mandatory 934 If a system is capable of sending and receiving the control word on 935 PW types for which the control word is not mandatory, then each such 936 PW endpoint MUST be configurable with a parameter that specifies 937 whether the use of the control word is PREFERRED or NOT PREFERRED. 938 For each PW, there MUST be a default value of this parameter. This 939 specification does NOT state what the default value should be. 941 If a system is NOT capable of sending and receiving the control word 942 on PW types for which the control word is not mandatory, then it 943 behaves exactly as if it were configured for the use of the control 944 word to be NOT PREFERRED. 946 If a Label Mapping message for the PW has already been received but 947 no Label Mapping message for the PW has yet been sent, then the 948 procedure is as follows: 950 -i. If the received Label Mapping message has c=0, send a Label 951 Mapping message with c=0; the control word is not used. 952 -ii. If the received Label Mapping message has c=1, and the PW is 953 locally configured such that the use of the control word is 954 preferred, then send a Label Mapping message with c=1; the 955 control word is used. 956 -iii. If the received Label Mapping message has c=1, and the PW is 957 locally configured such that the use of the control word is 958 not preferred or the control word is not supported, then act 959 as if no Label Mapping message for the PW had been received 960 (That is: proceed to the next paragraph). 962 If a Label Mapping message for the PW has not already been received 963 (or if the received Label Mapping message had c=1 and either local 964 configuration says that the use of the control word is not preferred 965 or the control word is not supported), then send a Label Mapping 966 message in which the c bit is set to correspond to the locally 967 configured preference for use of the control word. (That is, set c=1 968 if locally configured to prefer the control word, and set c=0 if 969 locally configured to prefer not to use the control word or if the 970 control word is not supported). 972 The next action depends on what control message is next received for 973 that PW. The possibilities are as follows: 975 -i. A Label Mapping message with the same c bit value as 976 specified in the Label Mapping message that was sent. PW 977 setup is now complete, and the control word is used if c=1 978 but is not used if c=0. 980 -ii. A Label Mapping message with c=1, but the Label Mapping 981 message that was sent has c=0. In this case, ignore the 982 received Label Mapping message and continue to wait for the 983 next control message for the PW. 985 -iii. A Label Mapping message with c=0, but the Label Mapping 986 message that was sent has c=1. In this case, send a Label 987 Withdraw message with a "Wrong C-bit" status code, followed 988 by a Label Mapping message that has c=0. PW setup is now 989 complete, and the control word is not used. 991 -iv. A Label Withdraw message with the "Wrong c-bit" status code. 992 Treat as a normal Label Withdraw, but do not respond. 993 Continue to wait for the next control message for the PW. 995 If at any time after a Label Mapping message has been received a 996 corresponding Label Withdraw or Release is received, the action taken 997 is the same as for any Label Withdraw or Release that might be 998 received at any time. 1000 If both endpoints prefer the use of the control word, this procedure 1001 will cause it to be used. If either endpoint prefers not to use the 1002 control word or does not support the control word, this procedure 1003 will cause it not to be used. If one endpoint prefers to use the 1004 control word but the other does not, the one that prefers not to use 1005 it has no extra protocol to execute; it just waits for a Label 1006 Mapping message that has c=0. 1008 7.3. Control-Word Renegotiation by Label Request Message 1010 It is possible that after the PW C-bit negotation procedure described 1011 above is completed, the local PE is re-provisioned with a different 1012 control word preference. Therefore once the Control-Word negotation 1013 procedures are completed, the procedure can be restarted as follows: 1014 -i. If local PE has previously sent a Label Mapping message, it 1015 MUST send a Label Withdraw message to remote PE and wait 1016 until it has received a Label Release message from the 1017 remote PE. 1018 -ii. the local PE MUST send a label release message to the remote 1019 PE for the specific label associated with the FEC that was 1020 advertized for this specific PW. Note: the above-mentioned 1021 steps of the Label Release message and Label Withdraw 1022 message are not required to be excuted in any specific 1023 sequence. 1024 -iii. The local PE MUST send a Label Request message to the peer 1025 PE, and then MUST wait until it receives a Label Mapping 1026 message containing the remote PE current configured 1027 preference for use of control word. 1029 Once the remote PE has successfully processed the Label Withdraw 1030 message and Label Release messages, it will reset the C-Bit 1031 negotation state machine and its use of control word with the locally 1032 configured preference. 1034 From this point on the local and remote PEs will follow the C-bit 1035 negotaiation procedures defined in the previous section. 1037 The above C-bit renegotation process SHOULD NOT be interupted until 1038 it is completed, or unpredictable results might occur. 1040 7.4. Sequencing Considerations 1042 In the case where the router considers the sequence number field in 1043 the control word, it is important to note the following details when 1044 advertising labels. 1046 7.4.1. Label Advertisements 1048 After a label has been withdrawn by the output router and/or released 1049 by the input router, care must be taken not to advertise (re-use) the 1050 same released label until the output router can be reasonably certain 1051 that old packets containing the released label no longer persist in 1052 the MPLS-enabled network. 1054 This precaution is required to prevent the imposition router from 1055 restarting packet forwarding with a sequence number of 1 when it 1056 receives a Label Mapping message that binds the same FEC to the same 1057 label if there are still older packets in the network with a sequence 1058 number between 1 and 32768. For example, if there is a packet with a 1059 sequence number=n, where n is in the interval [1,32768] traveling 1060 through the network, it would be possible for the disposition router 1061 to receive that packet after it re-advertises the label. Since the 1062 label has been released by the imposition router, the disposition 1063 router SHOULD be expecting the next packet to arrive with a sequence 1064 number of 1. Receipt of a packet with a sequence number equal to n 1065 will result in n packets potentially being rejected by the 1066 disposition router until the imposition router imposes a sequence 1067 number of n+1 into a packet. Possible methods to avoid this are for 1068 the disposition router always to advertise a different PW label, or 1069 for the disposition router to wait for a sufficient time before 1070 attempting to re-advertise a recently released label. This is only 1071 an issue when sequence number processing is enabled at the 1072 disposition router. 1074 7.4.2. Label Release 1076 In situations where the imposition router wants to restart forwarding 1077 of packets with sequence number 1, the router shall 1) send to the 1078 disposition router a Label Release Message, and 2) send to the 1079 disposition router a Label Request message. When sequencing is 1080 supported, advertisement of a PW label in response to a Label Request 1081 message MUST also consider the issues discussed in the section on 1082 Label Advertisements. 1084 8. IANA Considerations 1086 In general IANA needs to update any references in the registries 1087 referring to RFC4447 to this document. 1089 8.1. LDP TLV TYPE 1091 This document uses several new LDP TLV types; IANA already maintains 1092 a registry of name "TLV TYPE NAME SPACE" defined by RFC 5036. Any 1093 references to RFC4447 need to be updated to reference this document. 1095 8.2. LDP Status Codes 1097 This document uses several new LDP status codes; IANA already 1098 maintains a registry of name "STATUS CODE NAME SPACE" defined by RFC 1099 5036. Any references to RFC4447 need to be updated to reference this 1100 document. 1102 8.3. FEC Type Name Space 1104 This document uses two new FEC element types, 0x80 and 0x81, from the 1105 registry "FEC Type Name Space" for the Label Distribution Protocol 1106 (LDP RFC 5036). Any references to RFC4447 need to be updated to 1107 reference this document. 1109 9. Security Considerations 1111 This document specifies the LDP extensions that are needed for 1112 setting up and maintaining pseudowires. The purpose of setting up 1113 pseudowires is to enable Layer 2 frames to be encapsulated in MPLS 1114 and transmitted from one end of a pseudowire to the other. Therefore 1115 we treat the security considerations for both the data plane and the 1116 control plane. 1118 9.1. Data-Plane Security 1120 With regard to the security of the data plane, the following areas 1121 must be considered: 1123 - MPLS PDU inspection. 1124 - MPLS PDU spoofing. 1126 - MPLS PDU alteration. 1127 - MPLS PSN protocol security. 1128 - Access Circuit security. 1129 - Denial of service prevention on the PE routers. 1131 When an MPLS PSN is used to provide pseudowire service, there is a 1132 perception that security MUST be at least equal to the currently 1133 deployed Layer 2 native protocol networks that the MPLS/PW network 1134 combination is emulating. This means that the MPLS-enabled network 1135 SHOULD be isolated from outside packet insertion in such a way that 1136 it SHOULD NOT be possible to insert an MPLS packet into the network 1137 directly. To prevent unwanted packet insertion, it is also important 1138 to prevent unauthorized physical access to the PSN, as well as 1139 unauthorized administrative access to individual network elements. 1141 As mentioned above, an MPLS-enabled network should not accept MPLS 1142 packets from its external interfaces (i.e., interfaces to CE devices 1143 or to other providers' networks) unless the top label of the packet 1144 was legitimately distributed to the system from which the packet is 1145 being received. If the packet's incoming interface leads to a 1146 different SP (rather than to a customer), an appropriate trust 1147 relationship must also be present, including the trust that the other 1148 SP also provides appropriate security measures. 1150 The three main security problems faced when using an MPLS-enabled 1151 network to transport PWs are spoofing, alteration, and inspection. 1152 First, there is a possibility that the PE receiving PW PDUs will get 1153 a PDU that appears to be from the PE transmitting the PW into the 1154 PSN, but that was not actually transmitted by the PE originating the 1155 PW. (That is, the specified encapsulations do not by themselves 1156 enable the decapsulator to authenticate the encapsulator.) A second 1157 problem is the possibility that the PW PDU will be altered between 1158 the time it enters the PSN and the time it leaves the PSN (i.e., the 1159 specified encapsulations do not by themselves assure the decapsulator 1160 of the packet's integrity.) A third problem is the possibility that 1161 the PDU's contents will be seen while the PDU is in transit through 1162 the PSN (i.e., the specification encapsulations do not ensure 1163 privacy.) How significant these issues are in practice depends on 1164 the security requirements of the applications whose traffic is being 1165 sent through the tunnel, and how secure the PSN itself is. 1167 9.2. Control-Plane Security 1169 General security considerations with regard to the use of LDP are 1170 specified in section 5 of RFC 5036. Those considerations also apply 1171 to the case where LDP is used to set up pseudowires. 1173 A pseudowire connects two attachment circuits. It is important to 1174 make sure that LDP connections are not arbitrarily accepted from 1175 anywhere, or else a local attachment circuit might get connected to 1176 an arbitrary remote attachment circuit. Therefore, an incoming LDP 1177 session request MUST NOT be accepted unless its IP source address is 1178 known to be the source of an "eligible" LDP peer. The set of 1179 eligible peers could be pre-configured (either as a list of IP 1180 addresses, or as a list of address/mask combinations), or it could be 1181 discovered dynamically via an auto-discovery protocol that is itself 1182 trusted. (Obviously, if the auto-discovery protocol were not 1183 trusted, the set of "eligible peers" it produces could not be 1184 trusted.) 1186 Even if an LDP connection request appears to come from an eligible 1187 peer, its source address may have been spoofed. Therefore, some 1188 means of preventing source address spoofing must be in place. For 1189 example, if all the eligible peers are in the same network, source 1190 address filtering at the border routers of that network could 1191 eliminate the possibility of source address spoofing. 1193 The LDP MD5 authentication key option, as described in section 2.9 of 1194 RFC 5036, MUST be implemented, and for a greater degree of security, 1195 it must be used. This provides integrity and authentication for the 1196 LDP messages and eliminates the possibility of source address 1197 spoofing. Use of the MD5 option does not provide privacy, but 1198 privacy of the LDP control messages is not usually considered 1199 important. As the MD5 option relies on the configuration of pre- 1200 shared keys, it does not provide much protection against replay 1201 attacks. In addition, its reliance on pre-shared keys may make it 1202 very difficult to deploy when the set of eligible neighbors is 1203 determined by an auto-configuration protocol. 1205 When the Generalized PWid FEC Element is used, it is possible that a 1206 particular LDP peer may be one of the eligible LDP peers but may not 1207 be the right one to connect to the particular attachment circuit 1208 identified by the particular instance of the Generalized PWid FEC 1209 element. However, given that the peer is known to be one of the 1210 eligible peers (as discussed above), this would be the result of a 1211 configuration error, rather than a security problem. Nevertheless, 1212 it may be advisable for a PE to associate each of its local 1213 attachment circuits with a set of eligible peers rather than have 1214 just a single set of eligible peers associated with the PE as a 1215 whole. 1217 10. Acknowledgments 1219 The authors wish to acknowledge the contributions of Vach Kompella, 1220 Vanson Lim, Wei Luo, Himanshu Shah, and Nick Weeds. 1222 11. Normative References 1224 [RFC2119] Bradner S., "Key words for use in RFCs to Indicate 1225 Requirement Levels", RFC 2119, March 1997 1227 [RFC5036] "LDP Specification." L. Andersson, P. Ed. 1228 Minei, I. Ed. B. Thomas. January 2001. RFC5036 1230 [RFC3032] "MPLS Label Stack Encoding", E. Rosen, Y. Rekhter, 1231 D. Tappan, G. Fedorkow, D. Farinacci, T. Li, A. Conta. 1232 RFC3032 1234 [RFC4446] "IANA Allocations for pseudo Wire Edge to Edge Emulation 1235 (PWE3)" L. Martini RFC4446 , April 2006 1237 [RFC7358] "Label Advertisement Discipline for LDP Forwarding 1238 Equivalence Classes (FECs)", K. Raza, S. Boutros, L. Martini, 1239 RFC7358, October 2014 1241 12. Informative References 1243 [RFC4842] "Synchronous Optical Network/Synchronous Digital Hierarchy 1244 (SONET/SDH) Circuit Emulation over Packet (CEP)", A. Malis, 1245 P. Pate, R. Cohen, Ed., D. Zelig, RFC4842, April 2007 1247 [RFC4553] "Structure-Agnostic Time Division Multiplexing (TDM) over 1248 Packet (SAToP)", Vainshtein A. Ed. Stein, Ed. YJ. RFC4553, 1249 June 2006 1251 [RFC4619] "Encapsulation Methods for Transport of Frame Relay over 1252 Multiprotocol Label Switching (MPLS) Networks", Martini L. Ed. 1253 C. Kawa Ed. A. Malis Ed. RFC4619, September 2006 1255 [RFC4717] "Encapsulation Methods for Transport of Asynchronous 1256 Transfer Mode (ATM) over MPLS Networks", Martini L. Jayakumar J. 1257 Bocci M. El-Aawar N. Brayley J. Koleyni G. RFC4717, 1258 December 2006 1260 [RFC4618] "Encapsulation Methods for Transport of PPP/High-Level 1261 Data Link Control (HDLC) Frames over MPLS Networks", Martini L. 1262 Rosen E. Heron G. Malis A. RFC4618, September 2006 1264 [RFC4448] "Encapsulation Methods for Transport of Ethernet over 1265 MPLS Networks", Martini L. Ed. Rosen E. El-Aawar N. Heron G. 1266 RFC4448, April 2006. 1268 [RFC4447] "Pseudowire Setup and Maintenance Using the Label 1269 Distribution Protocol (LDP)", Martini L. Ed. Rosen E. 1270 El-Aawar N. Smith T. Heron G. RFC4447, April 2006 1272 [ANSI] American National Standards Institute, "Synchronous Optical 1273 Network Formats," ANSI T1.105-1995. 1275 [ITUG] ITU Recommendation G.707, "Network Node Interface For The 1276 Synchronous Digital Hierarchy", 1996. 1278 [RFC3985] "PWE3 Architecture" Bryant, et al., RFC3985. 1280 [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and 1281 Languages", BCP 18, RFC 2277, January 1998. 1283 13. Author Information 1285 Luca Martini 1286 Cisco Systems, Inc. 1287 9155 East Nichols Avenue, Suite 400 1288 Englewood, CO, 80112 1289 e-mail: lmartini@cisco.com 1291 Giles Heron 1292 Cisco Systems 1293 10 New Square 1294 Bedfont Lakes 1295 Feltham 1296 Middlesex 1297 TW14 8HA 1298 UK 1299 e-mail: giheron@cisco.com 1301 14. Additional Historical Contributing Authors 1303 This historical list is from the original RFC, and is not updated. It 1304 is intended for recognition of their work on RFC4447. 1306 Nasser El-Aawar 1307 Level 3 Communications, LLC. 1308 1025 Eldorado Blvd. 1309 Broomfield, CO, 80021 1310 e-mail: nna@level3.net 1312 Eric C. Rosen 1313 Cisco Systems, Inc. 1314 1414 Massachusetts Avenue 1315 Boxborough, MA 01719 1316 e-mail: erosen@cisco.com 1318 Dan Tappan 1319 Cisco Systems, Inc. 1320 1414 Massachusetts Avenue 1321 Boxborough, MA 01719 1322 e-mail: tappan@cisco.com 1324 Toby Smith 1325 Google 1326 6425 Penn Ave. #700 1327 Pittsburgh, PA 15206 1328 e-mail: tob@google.com 1330 Dimitri Vlachos 1331 Riverbed Technology 1332 e-mail: dimitri@riverbed.com 1334 Jayakumar Jayakumar, 1335 Cisco Systems Inc. 1336 3800 Zanker Road, MS-SJ02/2, 1337 San Jose, CA, 95134 1338 e-mail: jjayakum@cisco.com 1339 Alex Hamilton, 1340 Cisco Systems Inc. 1341 485 East Tasman Drive, MS-SJC07/3, 1342 San Jose, CA, 95134 1343 e-mail: tahamilt@cisco.com 1345 Steve Vogelsang 1346 ECI Telecom 1347 Omega Corporate Center 1348 1300 Omega Drive 1349 Pittsburgh, PA 15205 1350 e-mail: stephen.vogelsang@ecitele.com 1352 John Shirron 1353 ECI Telecom 1354 Omega Corporate Center 1355 1300 Omega Drive 1356 Pittsburgh, PA 15205 1357 e-mail: john.shirron@ecitele.com 1359 Andrew G. Malis 1360 Verizon 1361 60 Sylvan Rd. 1362 Waltham, MA 02451 1363 e-mail: andrew.g.malis@verizon.com 1365 Vinai Sirkay 1366 Reliance Infocomm 1367 Dhirubai Ambani Knowledge City 1368 Navi Mumbai 400 709 1369 e-mail: vinai@sirkay.com 1371 Vasile Radoaca 1372 Nortel Networks 1373 600 Technology Park 1374 Billerica MA 01821 1375 e-mail: vasile@nortelnetworks.com 1376 Chris Liljenstolpe 1377 149 Santa Monica Way 1378 San Francisco, CA 94127 1379 e-mail: ietf@cdl.asgaard.org 1381 Dave Cooper 1382 Global Crossing 1383 960 Hamlin Court 1384 Sunnyvale, CA 94089 1385 e-mail: dcooper@gblx.net 1387 Kireeti Kompella 1388 Juniper Networks 1389 1194 N. Mathilda Ave 1390 Sunnyvale, CA 94089 1391 e-mail: kireeti@juniper.net 1393 Copyright Notice 1395 Copyright (c) 2015 IETF Trust and the persons identified as the 1396 document authors. 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