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Found 'MUST not' in this paragraph: This document describes the so called "draft-martini" protocol with is used in many deployed implementations. This document and it's contents have been since superseded by the Pseudo Wire Edge to Edge Working Group specifications: [RFC4447], [RFC4385], [RFC4448], [ATM], [RFC4618], [RFC4619], [RFC4553], [CEP] and related documents. This document serves as a documentation of current implementations, and MUST not be used for new implementations. The PWE3 LDP control [RFC4447] document, which is backward compatible with this document MUST be used for all new implementations of this protocol. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. 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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Luca Martini (Editor) 3 Internet Draft Eric C. Rosen (Editor) 4 Expiration Date: March 2007 Cisco Systems, Inc. 6 Nasser El-Aawar (Editor) 7 Level 3 Communications, LLC. 9 September 2006 11 Transport of Layer 2 Frames Over MPLS 13 draft-martini-l2circuit-trans-mpls-19.txt 15 Status of this Memo 17 By submitting this Internet-Draft, each author represents that any 18 applicable patent or other IPR claims of which he or she is aware 19 have been or will be disclosed, and any of which he or she becomes 20 aware will be disclosed, in accordance with Section 6 of BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF), its areas, and its working groups. Note that other 24 groups may also distribute working documents as Internet-Drafts. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 The list of current Internet-Drafts can be accessed at 32 http://www.ietf.org/1id-abstracts.html 34 The list of Internet-Draft Shadow Directories can be accessed at 35 http://www.ietf.org/shadow.html. 37 Abstract 39 This document describes methods for transporting the Protocol Data 40 Units (PDUs) of layer 2 protocols such as Frame Relay, ATM AAL5, 41 Ethernet, and providing a SONET circuit emulation service across an 42 MPLS network. 44 Table of Contents 46 1 Specification of Requirements .......................... 3 47 2 Special Note ........................................... 3 48 3 Co-authors ............................................. 3 49 4 Introduction ........................................... 4 50 5 Tunnel Labels and VC Labels ............................ 4 51 6 Protocol-Specific Details .............................. 6 52 6.1 Frame Relay ............................................ 6 53 6.2 ATM .................................................... 6 54 6.2.1 ATM AAL5 VCC Transport ................................. 6 55 6.2.2 ATM Transparent Cell Transport ......................... 6 56 6.2.3 ATM VCC and VPC Cell Transport ......................... 7 57 6.2.4 OAM Cell Support ....................................... 7 58 6.2.5 ILMI Support ........................................... 8 59 6.3 Ethernet VLAN .......................................... 8 60 6.4 Ethernet ............................................... 8 61 6.5 HDLC ................................................... 8 62 6.6 PPP .................................................... 9 63 7 LDP .................................................... 9 64 7.1 Interface Parameters Field ............................. 11 65 7.2 C Bit handling procedures .............................. 12 66 7.2.1 VC types for which the control word is REQUIRED ........ 12 67 7.2.2 VC types for which the control word is NOT mandatory ... 12 68 7.2.3 Status codes ........................................... 16 69 7.3 LDP label Withdrawal procedures ........................ 16 70 7.4 Sequencing Considerations .............................. 16 71 7.4.1 Label Mapping Advertisements ........................... 17 72 7.4.2 Label Mapping Release .................................. 17 73 8 IANA Considerations .................................... 17 74 9 Security Considerations ................................ 18 75 10 Full Copyright Statement ............................... 18 76 11 Intellectual Property Statement ........................ 18 77 12 Nomative References .................................... 19 78 13 Informative References ................................. 20 79 14 Contributing Author Information ........................ 20 80 15 Author Information ..................................... 22 82 1. Specification of Requirements 84 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 85 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 86 document are to be interpreted as described in RFC 2119. 88 2. Special Note 90 This document describes the so called "draft-martini" protocol with 91 is used in many deployed implementations. This document and it's 92 contents have been since superseded by the Pseudo Wire Edge to Edge 93 Working Group specifications: [RFC4447], [RFC4385], [RFC4448], [ATM], 94 [RFC4618], [RFC4619], [RFC4553], [CEP] and related documents. This 95 document serves as a documentation of current implementations, and 96 MUST not be used for new implementations. The PWE3 LDP control 97 [RFC4447] document, which is backward compatible with this document 98 MUST be used for all new implementations of this protocol. 100 3. Co-authors 102 The following are also co-authors of this document: 104 Daniel Tappan Cisco Systems 105 Kireeti Kompella Juniper Networks, Inc. 106 Steve Vogelsang Laurel Networks, Inc. 107 John Shirron Laurel Networks, Inc. 108 Vinai Sirkay Reliance Infocomm 109 Giles Heron Tellabs 110 Andrew G. Malis Tellabs 111 Dimitri Stratton Vlachos Mazu Networks,Inc. 112 Chris Liljenstolpe Alcatel 113 Toby Smith Network Appliance. Inc. 114 Jayakumar Jayakumar Cisco Systems Inc. 115 Alex Hamilton Cisco Systems Inc. 116 Vasile Radoaca Nortel Networks 117 Dave Cooper Global Crossing 119 4. Introduction 121 In an MPLS network, it is possible to carry the Protocol Data Units 122 (PDUs) of layer 2 protocols by prepending an MPLS label stack to 123 these PDUs. This document specifies the necessary label distribution 124 procedures for accomplishing this using the encapsulation methods in 125 [7]. We restrict discussion to the case of point-to-point transport. 126 QoS related issues are not discussed in this draft. This document 127 describes methods for transporting a number of protocols; in some 128 cases, transporting a particular protocol may have several modes of 129 operation. Each of these protocols and/or modes may be implemented 130 independently. 132 An accompanying document [8] also describes a method for transporting 133 time division multiplexed (TDM) digital signals (TDM circuit 134 emulation) over a packet-oriented MPLS network. The transmission 135 system for circuit-oriented TDM signals is the Synchronous Optical 136 Network (SONET)[5]/Synchronous Digital Hierarchy (SDH) [6]. To 137 support TDM traffic, which includes voice, data, and private leased 138 line service, the MPLS network must emulate the circuit 139 characteristics of SONET/SDH payloads. MPLS labels and a new circuit 140 emulation header are used to encapsulate TDM signals and provide the 141 Circuit Emulation Service over MPLS (CEM). 143 5. Tunnel Labels and VC Labels 145 Suppose it is desired to transport layer 2 PDUs from ingress LSR R1 146 to egress LSR R2, across an intervening MPLS network. We assume that 147 there is an LSP from R1 to R2. That is, we assume that R1 can cause a 148 packet to be delivered to R2 by pushing some label onto the packet 149 and sending the result to one of its adjacencies. Call this label the 150 "tunnel label", and the corresponding LSP the "tunnel LSP". 152 The tunnel LSP merely gets packets from R1 to R2, the corresponding 153 label doesn't tell R2 what to do with the payload, and in fact if 154 penultimate hop popping is used, R2 may never even see the 155 corresponding label. (If R1 itself is the penultimate hop, a tunnel 156 label may not even get pushed on.) Thus if the payload is not an IP 157 packet, there must be a label, which becomes visible to R2, that 158 tells R2 how to treat the received packet. Call this label the "VC 159 label". 161 So when R1 sends a layer 2 PDU to R2, it first pushes a VC label on 162 its label stack, and then (if R1 is not adjacent to R2) pushes on a 163 tunnel label. The tunnel label gets the MPLS packet from R1 to R2; 164 the VC label is not visible until the MPLS packet reaches R2. R2's 165 disposition of the packet is based on the VC label. 167 Note that the tunnel could be a GRE encapsulated MPLS tunnel between 168 R1 and R2. In this case R1 would be adjacent to R2, and only the VC 169 label would be used, and the intervening network need only carry IP 170 packets. 172 If the payload of the MPLS packet is, for example, an ATM AAL5 PDU, 173 the VC label will generally correspond to a particular ATM VC at R2. 174 That is, R2 needs to be able to infer from the VC label the outgoing 175 interface and the VPI/VCI value for the AAL5 PDU. If the payload is a 176 Frame Relay PDU, then R2 needs to be able to infer from the VC label 177 the outgoing interface and the DLCI value. If the payload is an 178 Ethernet frame, then R2 needs to be able to infer from the VC label 179 the outgoing interface, and perhaps the VLAN identifier. This process 180 is unidirectional, and will be repeated independently for 181 bidirectional operation. It is REQUIRED to assign the same VC ID, and 182 VC type for a given circuit in both directions. The group ID (see 183 below) MUST NOT be required to match in both directions. The 184 transported frame MAY be modified when it reaches the egress router. 185 If the header of the transported layer 2 frame is modified, this MUST 186 be done at the egress LSR only. 188 Note that the VC label must always be at the bottom of the label 189 stack, and the tunnel label, if present, must be immediately above 190 the VC label. Of course, as the packet is transported across the MPLS 191 network, additional labels may be pushed on (and then popped off) as 192 needed. Even R1 itself may push on additional labels above the tunnel 193 label. If R1 and R2 are directly adjacent LSRs, then it may not be 194 necessary to use a tunnel label at all. 196 This document does not specify a method for distributing the tunnel 197 label or any other labels that may appear above the VC label on the 198 stack. Any acceptable method of MPLS label distribution will do. 200 This document does specify a method for assigning and distributing 201 the VC label. Static label assignment MAY be used, and 202 implementations SHOULD provide support for this. When signaling is 203 used, the VC label MUST be distributed from R2 to R1 using LDP in the 204 downstream unsolicited mode; this requires that an LDP session be 205 created between R1 and R2. It should be noted that this LDP session 206 is not necessarily transported along the same path as the Layer 2 207 PDUs. [1] In addition, when using LDP to distribute the VC label, 208 liberal label retention mode SHOULD be used. However, as required in 209 [1], the label request operation (mainly used by conservative label 210 retention mode) MUST be implemented. VC labels MUST be allocated from 211 the per-platform label space. 213 Note that this technique allows an unbounded number of layer 2 "VCs" 214 to be carried together in a single "tunnel". Thus it scales quite 215 well in the network backbone. 217 While this document currently defines the emulation of Frame Relay 218 and ATM PVC services, it specifically does not preclude future 219 enhancements to support switched service (SVC and SPVC) emulation. 221 6. Protocol-Specific Details 223 6.1. Frame Relay 225 The Frame Relay PDUs are encapsulated according to the procedures 226 defined in [7]. The MPLS edge LSR MUST provide Frame Relay PVC status 227 signaling to the Frame Relay network. If the MPLS edge LSR detects a 228 service affecting condition as defined in [2] Q.933 Annex A.5 sited 229 in IA FRF1.1, it MUST withdraw the label that corresponds to the 230 frame relay DLCI. The Egress LSR SHOULD generate the corresponding 231 errors and alarms as defined in [2] on the egress Frame relay VC. 233 6.2. ATM 235 6.2.1. ATM AAL5 VCC Transport 237 ATM AAL5 CSPS-SDUs are encapsulated according to [7] ATM AAL5 CPCS- 238 SDU mode. This mode allows the transport of ATM AAL5 CSPS-SDUs 239 traveling on a particular ATM PVC across the MPLS network to another 240 ATM PVC. 242 6.2.2. ATM Transparent Cell Transport 244 This mode is similar to the Ethernet port mode. Every cell that is 245 received at the ingress ATM port on the ingress LSR, R1, is 246 encapsulated according to [7], ATM cell mode, and sent across the LSP 247 to the egress LSR, R2. This mode allows an ATM port to be connected 248 to only one other ATM port. [7] allows for grouping of multiple cells 249 into a single MPLS frame. Grouping of ATM cells is OPTIONAL for 250 transmission at the ingress LSR, R1. If the Egress LSR R2 supports 251 cell concatenation the ingress LSR, R1, should only concatenate cells 252 up to the "Maximum Number of concatenated ATM cells" parameter 253 received as part of the FEC element. 255 6.2.3. ATM VCC and VPC Cell Transport 257 This mode is similar to the ATM AAL5 VCC transport except that cells 258 are transported. Every cell that is received on a pre-defined ATM 259 PVC, or ATM PVP, at the ingress ATM port on the ingress LSR, R1, is 260 encapsulated according to [7], ATM cell mode, and sent across the LSP 261 to the egress LSR R2. Grouping of ATM cells is OPTIONAL for 262 transmission at the ingress LSR, R1. If the Egress LSR R2 supports 263 cell concatenation the ingress LSR, R1, MUST only concatenate cells 264 up to the "Maximum Number of concatenated ATM cells in a frame" 265 parameter received as part of the FEC element. 267 6.2.4. OAM Cell Support 269 OAM cells MAY be transported on the VC LSP. When the LSR is operating 270 in AAL5 CPCS-SDU transport mode if it does not support transport of 271 ATM cells, the LSR MUST discard incoming MPLS frames on an ATM VC LSP 272 that contain a VC label with the T bit set [7]. When operating in 273 AAL5 SDU transport mode an LSR that supports transport of OAM cells 274 using the T bit defined in [7], or an LSR operating in any of the 275 three cell transport modes MUST follow the procedures outlined in [9] 276 section 8 for mode 0 only, in addition to the applicable procedures 277 specified in [6]. 279 6.2.4.1. OAM Cell Emulation Mode 281 AN LSR that does not support transport of OAM cells across an LSP MAY 282 provide OAM support on ATM PVCs using the following procedures: 284 A pair of LSRs MAY emulate a bidirectional ATM VC by two uni- 285 directional LSPs. If an F5 end-to-end OAM cell is received from a 286 ATM VC, by either LSR that is transporting this ATM VC, with a 287 loopback indication value of 1, and the LSR has a label mapping for 288 the ATM VC, then the LSR MUST decrement the loopback indication value 289 and loop back the cell on the ATM VC. Otherwise the loopback cell 290 MUST be discarded by the LSR. 292 The ingress LSR, R1, may also optionally be configured to 293 periodically generate F5 end-to-end loopback OAM cells on a VC. If 294 the LSR fails to receive a response to an F5 end-to-end loopback OAM 295 cell for a pre-defined period of time it MUST withdraw the label 296 mapping for the VC. 298 If an ingress LSR, R1, receives an AIS F5 OAM cell, fails to receive 299 a pre-defined number of the End-to-End loop OAM cells, or a physical 300 interface goes down, it MUST withdraw the label mappings for all VCs 301 associated with the failure. When a VC label mapping is withdrawn, 302 the egress LSR, R2, MUST generate AIS F5 OAM cells on the VC 303 associated with the withdrawn label mapping. In this mode it is very 304 useful to apply a unique group ID to each interface. In the case 305 where a physical interface goes down, a wild card label withdraw can 306 be sent to all LDP neighbors, greatly reducing the signaling response 307 time. 309 6.2.5. ILMI Support 311 An MPLS edge LSR MAY provide an ATM ILMI to the ATM edge switch. If 312 an ingress LSR receives an ILMI message indicating that the ATM edge 313 switch has deleted a VC, or if the physical interface goes down, it 314 MUST withdraw the label mappings for all VCs associated with the 315 failure. When a VC label mapping is withdrawn, the egress LSR SHOULD 316 notify its client of this failure by deleting the VC using ILMI. 318 6.3. Ethernet VLAN 320 The Ethernet frame will be encapsulated according to the procedures 321 in [12]. It should be noted that if the VLAN identifier is modified 322 by the egress LSR, according to the procedures outlined above, the 323 Ethernet spanning tree protocol might fail to work properly. If the 324 LSR detects a failure on the Ethernet physical port, or the port is 325 administratively disabled, it MUST withdraw the label mappings for 326 all VCs associated with the port. 328 6.4. Ethernet 330 The Ethernet frame will be encapsulated according to the procedures 331 in [12]. If the LSR detects a failure on the Ethernet physical port, 332 or the port is administratively disabled, the corresponding VC label 333 mapping MUST be withdrawn. 335 6.5. HDLC 337 HDLC frames are encapsulated according to the procedures in [7]. If 338 the MPLS edge LSR detects that the physical link has failed, or the 339 port is administratively disabled, it MUST withdraw the label mapping 340 that corresponds to the HDLC link. 342 6.6. PPP 344 PPP frames are encapsulated according to the procedures in [7]. If 345 the MPLS edge LSR detects that the physical link has failed, or the 346 port is administratively disabled, it MUST withdraw the label mapping 347 that corresponds to the PPP link. 349 7. LDP 351 The VC label bindings are distributed using the LDP downstream 352 unsolicited mode described in [1]. The LSRs will establish an LDP 353 session using the Extended Discovery mechanism described in [1, 354 section 2.4.2 and 2.5], for this purpose a new type of FEC element is 355 defined. The FEC element type is 128. [note1] Only a single VC FEC 356 element MUST be advertised per LDP VC label. The Virtual Circuit FEC 357 element, is defined as follows: 359 0 1 2 3 360 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 1 361 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 362 | VC tlv |C| VC Type |VC info Length | 363 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 364 | Group ID | 365 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 366 | VC ID | 367 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 368 | Interface parameters | 369 | " | 370 | " | 371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 373 - VC Type 375 A 15 bit quantity containing a value which represents the type of 376 VC. Assigned Values are: 378 VC Type Description 380 0x0001 Frame Relay DLCI 381 0x0002 ATM AAL5 VCC transport 382 0x0003 ATM transparent cell transport 383 0x0004 Ethernet VLAN 384 0x0005 Ethernet 385 0x0006 HDLC 386 0x0007 PPP 387 0x8008 CEM [8] 388 0x0009 ATM VCC cell transport 389 0x000A ATM VPC cell transport 391 - Control word bit (C) 393 The highest order bit (C) of the VC type is used to flag the 394 presence of a control word (defined in [7]) as follows: 395 bit 15 = 1 control word present on this VC. 396 bit 15 = 0 no control word present on this VC. 398 Please see the section "C Bit handling procedures" for further 399 explenation. 401 - VC information length 403 Length of the VC ID field and the interface parameters field in 404 octets. If this value is 0, then it references all VCs using the 405 specified group ID and there is no VC ID present, nor any 406 interface parameters. 408 - Group ID 410 An arbitrary 32 bit value which represents a group of VCs that is 411 used to create groups in the VC space. The group ID is intended 412 to be used as a port index, or a virtual tunnel index. To 413 simplify configuration a particular VC ID at ingress could be 414 part of the virtual tunnel for transport to the egress router. 415 The Group ID is very useful to send wild card label withdrawals 416 to remote LSRs upon physical port failure. 418 - VC ID 420 A non zero 32-bit connection ID that together with the VC type, 421 identifies a particular VC. 423 - Interface parameters 425 This variable length field is used to provide interface specific 426 parameters, such as interface MTU. 428 7.1. Interface Parameters Field 430 This field specifies interface specific parameters. When applicable, 431 it MUST be used to validate that the LSRs, and the ingress and egress 432 ports at the edges of the circuit, have the necessary capabilities to 433 interoperate with each other. The field structure is defined as 434 follows: 436 0 1 2 3 437 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 1 438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 439 | Parameter ID | Length | Variable Length Value | 440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 441 | Variable Length Value | 442 | " | 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 445 The parameter ID is defined as follows: 446 Parameter ID Length Description 448 0x01 4 Interface MTU in octets. 449 0x02 4 Maximum Number of concatenated ATM cells. 450 0x03 up to 82 Optional Interface Description string. 451 0x04 4 CEM [8] Payload Bytes. 452 0x05 4 CEM options. 454 The Length field is defined as the length of the interface parameter 455 including the parameter id and length field itself. Processing of the 456 interface parameters should continue when encountering unknown 457 interface parameters and they MUST be silently ignored. 459 - Interface MTU 461 A 2 octet value indicating the MTU in octets. This is the Maximum 462 Transmission Unit, excluding encapsulation overhead, of the 463 egress packet interface that will be transmitting the 464 decapsulated PDU that is received from the MPLS network. This 465 parameter is applicable only to VC types 1, 2, 4, 5, 6, and 7, 466 and is REQUIRED for these VC types. If this parameter does not 467 match in both directions of a specific VC, that VC MUST NOT be 468 enabled. 470 - Maximum Number of concatenated ATM cells 472 A 2 octet value specifying the maximum number of concatenated ATM 473 cells that can be processed as a single PDU by the egress LSR. An 474 ingress LSR transmitting concatenated cells on this VC can 475 concatenate a number of cells up to the value of this parameter, 476 but MUST NOT exceed it. This parameter is applicable only to VC 477 types 3, 9, and 0x0a, and is REQUIRED for these VC types. This 478 parameter does not need to match in both directions of a specific 479 VC. 481 - Optional Interface Description string 483 This arbitrary, OPTIONAL, interface description string can be 484 used to send an administrative description text string to the 485 remote LSR. This parameter is OPTIONAL, and is applicable to all 486 VC types. The interface description parameter string length is 487 variable, and can be from 0 to 80 octets. 489 - Payload Bytes 491 A 2 octet value indicating the the number of TDM payload octets 492 contained in all packets on the CEM stream, from 48 to 1,023 493 octets. All of the packets in a given CEM stream have the same 494 number of payload bytes. Note that there is a possibility that 495 the packet size may exceed the SPE size in the case of an STS-1 496 SPE, which could cause two pointers to be needed in the CEM 497 header, since the payload may contain two J1 bytes for 498 consecutive SPEs. For this reason, the number of payload bytes 499 must be less than or equal to 783 for STS-1 SPEs. 501 - CEM Options. An optional 16 Bit value of CEM Flags. See [8] for 502 the definition of the bit values. 504 7.2. C Bit handling procedures 506 7.2.1. VC types for which the control word is REQUIRED 508 The Label Mapping messages which are sent in order to set up these 509 VCs MUST have c=1. When a Label Mapping message for a VC of one of 510 these types is received, and c=0, a Label Release MUST be sent, with 511 an "Illegal C-bit" status code. In this case, the VC will not come 512 up. 514 7.2.2. VC types for which the control word is NOT mandatory 516 If a system is capable of sending and receiving the control word on 517 VC types for which the control word is not mandatory, then each such 518 VC endpoint MUST be configurable with a parameter that specifies 519 whether the use of the control word is PREFERRED or NOT PREFERRED. 521 For each VC, there MUST be a default value of this parameter. This 522 specification does NOT state what the default value should. 524 If a system is NOT capable of sending and receiving the control word 525 on VC types for which the control word is not mandatory, then it 526 behaves as exactly as if it were configured for the use of the 527 control word to be NOT PREFERRED. 529 If a Label Mapping message for the VC has already been received, but 530 no Label Mapping message for the VC has yet been sent, then the 531 procedure is the following: 532 -i. If the received Label Mapping message has c=0, send a Label 533 Mapping message with c=0, and the control word is not used. 534 -ii. If the received Label Mapping message has c=1, and the VC is 535 locally configured such that the use of the control word is 536 preferred, then send a Label Mapping message with c=1, and 537 the control word is used. 538 -iii. If the received Label Mapping message has c=1, and the VC is 539 locally configured such that the use of the control word is 540 not preferred or the control word is not supported, then act 541 as if no Label Mapping message for the VC had been received 542 (i.e., proceed to the next paragraph). 544 If a Label Mapping message for the VC has not already been received 545 (or if the received Label Mapping message had c=1 and either local 546 configuration says that the use of the control word is not preferred 547 or the control word is not supported), then send a Label Mapping 548 message in which the c bit is set to correspond to the locally 549 configured preference for use of the control word. (I.e., set c=1 if 550 locally configured to prefer the control word, set c=0 if locally 551 configured to prefer not to use the control word or if the control 552 word is not supported). 554 The next action depends on what control message is next received for 555 that VC. The possibilities are: 556 -i. A Label Mapping message with the same c bit value as 557 specified in the Label Mapping message that was sent. VC 558 setup is now complete, and the control word is used if c=1 559 but not used if c=0. 560 -ii. A Label Mapping message with c=1, but the Label Mapping 561 message that was sent has c=0. In this case, ignore the 562 received Label Mapping message, and continue to wait for the 563 next control message for the VC. 564 -iii. A Label Mapping message with c=0, but the Label Mapping 565 message that was sent has c=1. In this case, send a Label 566 Withdraw message with a "Wrong c-bit" status code, followed 567 by a Label Mapping message that has c=0. VC setup is now 568 complete, and the control word is not used. 570 -iv. A Label Withdraw message with the "Wrong c-bit" status code. 571 Treat as a normal Label Withdraw, but do not respond. 572 Continue to wait for the next control message for the VC. 574 If at any time after a Label Mapping message has been received, a 575 corresponding Label Withdraw or Release is received, the action taken 576 is the same as for any Label Withdraw or Release that might be 577 received at any time. 579 If both endpoints prefer the use of the control word, this procedure 580 will cause it to be used. If either endpoint prefers not to use the 581 control word, or does not support the control word, this procedure 582 will cause it not to be used. If one endpoint prefers to use the 583 control word but the other does not, the one that prefers not to use 584 it is has no extra protocol to execute, it just waits for a Label 585 Mapping message that has c=0. 587 The following diagram illustrate the above procedures: 589 ------------------ 590 Y | Received Label | N 591 -------| Mapping Msg? |-------------- 592 | ------------------ | 593 | | 594 -------------- | 595 | | | 596 | | | 597 ------- ------- | 598 | C=0 | | C=1 | | 599 ------- ------- | 600 | | | 601 | | | 602 | ---------------- | 603 | | Control Word | N | 604 | | Capable? |----------- | 605 | ---------------- | | 606 | Y | | | 607 | | | | 608 | ---------------- | | 609 | | Control Word | N | | 610 | | Preferred? |---- | | 611 | ---------------- | | | 612 | Y | | | | 613 | | | | ---------------- 614 | | | | | Control Word | 615 | | | | | Preferred? | 616 | | | | ---------------- 617 | | | | N | Y | 618 | | | | | | 619 Send Send Send Send Send Send 620 C=0 C=1 C=0 C=0 C=0 C=1 621 | | | | 622 | | | | 623 ---------------------------------- 624 | If receive the same as sent, | 625 | VC setup is complete. If not: | 626 ---------------------------------- 627 | | | | 628 | | | | 629 ------------------- ----------- 630 | Receive | | Receive | 631 | C=1 | | C=0 | 632 ------------------- ----------- 633 | | 634 | | 635 Wait for the Send 636 next message Wrong C-Bit 637 | 638 | 639 Send Label 640 Mapping Message 641 with C=0 643 7.2.3. Status codes 645 RFC 3036 has a range of Status Code values which are assigned by IANA 646 on a First Come, First Served basis. These are in the range 647 0x20000000-0x3effffff [note 2]. The following new status codes are 648 defined: 650 0x20000001 "Illegal C-Bit" 651 0x20000002 "Wrong C-Bit" 653 7.3. LDP label Withdrawal procedures 655 As mentioned above the Group ID field can be used to withdraw all VC 656 labels associated with a particular group ID. This procedure is 657 OPTIONAL, and if it is implemented the LDP label withdraw message 658 should be as follows: the VC information length field is set to 0, 659 the VC ID field is not present, and the interface parameters field is 660 not present. For the purpose of this document this is called the 661 "wild card withdraw procedure", and all LSRs implementing this design 662 are REQUIRED to accept such a withdraw message, but are not required 663 to send it. 665 The interface parameters field MUST NOT be present in any LDP VC 666 label withdrawal message or release message. A wild card release 667 message MUST include only the group ID.A Label Release message 668 initiated from the imposition router must always include the VC ID. 670 7.4. Sequencing Considerations 672 In the case where the router considers the sequence number field in 673 the control word, it is important to note the following when 674 advertising labels 676 7.4.1. Label Mapping Advertisements 678 After a label has been withdrawn by the disposition router and/or 679 released by the imposition router, care must be taken to not re- 680 advertise (re-use) the released label until the disposition router 681 can be reasonably certain that old packets containing the released 682 label no longer persist in the MPLS network. 684 This precaution is required to prevent the imposition router from 685 restarting packet forwarding with sequence number of 1 when it 686 receives the same label mapping if there are still older packets 687 persisting in the network with sequence number between 1 and 32768. 688 For example, if there is a packet with sequence number=n where n is 689 in the interval[1,32768] traveling through the network, it would be 690 possible for the disposition router to receive that packet after it 691 re-advertises the label. Since the label has been released by the 692 imposition router, the disposition router SHOULD be expecting the 693 next packet to arrive with sequence number to be 1. Receipt of a 694 packet with sequence number equal to n will result in n packets 695 potentially being rejected by the disposition router until the 696 imposition router imposes a sequence number of n+1 into a packet. 697 Possible methods to avoid this is for the disposition router to 698 always advertise a different VC label, or for the disposition router 699 to wait for a sufficient time before attempting to re-advertised a 700 recently released label. This is only an issue when sequence number 701 processing at the disposition router is enabled. 703 7.4.2. Label Mapping Release 705 In situations where the imposition router wants to restart forwarding 706 of packets with sequence number 1, the router shall 1) Send to 707 disposition router a label mapping release, and 2) Send to 708 disposition router a label mapping request. When sequencing is 709 supported, advertisement of a VC label in response to a label mapping 710 request MUST also consider the issues discussed in 5.3.1 712 8. IANA Considerations 714 As specified in this document, a Virtual Circuit FEC element contains 715 the VC Type field. VC Type value 0 is reserved. VC Type values 1 716 through 10 are defined in this document. VC Type values 11 through 63 717 are to be assigned by IANA using the "IETF Consensus" policy defined 718 in RFC2434. VC Type values 64 through 127 are to be assigned by IANA, 719 using the "First Come First Served" policy defined in RFC2434. VC 720 Type values 128 through 32767 are vendor-specific, and values in this 721 range are not to be assigned by IANA. 723 As specified in this document, a Virtual Circuit FEC element contains 724 the Interface Parameters field, which is a list of one or more 725 parameters, and each parameter is identified by the Parameter ID 726 field. Parameter ID value 0 is reserved. Parameter ID values 1 727 through 5 are defined in this document. Parameter ID values 6 728 through 63 are to be assigned by IANA using the "IETF Consensus" 729 policy defined in RFC2434. Parameter ID values 64 through 127 are to 730 be assigned by IANA, using the "First Come First Served" policy 731 defined in RFC2434. Parameter ID values 128 through 255 are vendor- 732 specific, and values in this range are not to be assigned by IANA. 734 9. Security Considerations 736 This document does not affect the underlying security issues of MPLS. 738 10. Full Copyright Statement 740 Copyright (C) The Internet Society (2006). 742 This document is subject to the rights, licenses and restrictions 743 contained in BCP 78, and except as set forth therein, the authors 744 retain all their rights. 746 This document and the information contained herein are provided on an 747 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 748 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 749 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 750 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 751 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 752 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 754 11. Intellectual Property Statement 756 The IETF takes no position regarding the validity or scope of any 757 Intellectual Property Rights or other rights that might be claimed to 758 pertain to the implementation or use of the technology described in 759 this document or the extent to which any license under such rights 760 might or might not be available; nor does it represent that it has 761 made any independent effort to identify any such rights. Information 762 on the procedures with respect to rights in RFC documents can be 763 found in BCP 78 and BCP 79. 765 Copies of IPR disclosures made to the IETF Secretariat and any 766 assurances of licenses to be made available, or the result of an 767 attempt made to obtain a general license or permission for the use of 768 such proprietary rights by implementers or users of this 769 specification can be obtained from the IETF on-line IPR repository at 770 http://www.ietf.org/ipr. 772 The IETF invites any interested party to bring to its attention any 773 copyrights, patents or patent applications, or other proprietary 774 rights that may cover technology that may be required to implement 775 this standard. Please address the information to the IETF at ietf- 776 ipr@ietf.org. 778 12. Nomative References 780 [RFC4447] "Pseudowire Setup and Maintenance using LDP", 781 Martini, L., et al., RFC4447,April 2006. 783 [RFC4385] "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word 784 for Use over an MPLS PSN", RFC4385, February 2006. 786 [CEP] "SONET/SDH Circuit Emulation Service Over Packet (CEP)", 787 draft-ietf-pwe3-sonet-11.txt (work in progress) 789 [RFC4553] "Structure-Agnostic TDM over Packet (SAToP)", RFC4553, 790 June 2006. 792 [RFC4619] "Frame Relay over Pseudo-Wires", RFC4619, August 2006. 794 [ATM] "Encapsulation Methods for Transport of ATM Cells/Frame Over IP 795 and MPLS Networks", draft-ietf-pwe3-atm-encap-05.txt (work in 796 progress) 798 [RFC4618] "Encapsulation Methods for Transport of PPP/HDLC Frames 799 MPLS Networks", RFC4618, August 2006 801 [RFC4448] "Encapsulation Methods for Transport of Ethernet Frames 802 Over MPLS Networks", RFC4448, April 2006. 804 [1] "LDP Specification." L. Andersson, P. Doolan, N. Feldman, A. 805 Fredette, B. Thomas. January 2001. RFC3036 807 [2] ITU-T Recommendation Q.933, and Q.922 Specification for Frame 808 Mode Basic call control, ITU Geneva 1995 810 [3] "MPLS Label Stack Encoding", E. Rosen, Y. Rekhter, D. Tappan, G. 811 Fedorkow, D. Farinacci, T. Li, A. Conta. RFC3032 813 [4] "IEEE 802.3ac-1998" IEEE standard specification. 815 [5] American National Standards Institute, "Synchronous Optical 816 Network Formats," ANSI T1.105-1995. 818 [6] ITU Recommendation G.707, "Network Node Interface For The 819 Synchronous Digital Hierarchy", 1996. 821 [7] "Encapsulation Methods for Transport of Layer 2 Frames Over MPLS" 822 draft-martini-l2circuit-encap-mpls-11.txt ( Work in progress ) 824 13. Informative References 826 [8] "SONET/SDH Circuit Emulation Service Over MPLS (CEM) 827 Encapsulation", draft-malis-sonet-ces-mpls-05.txt 828 (Work in progress) 830 [9] "Frame Based ATM over SONET/SDH Transport (FAST)," 2000. 832 [note1] FEC element type 128 is pending IANA approval. 833 [note2] Status codes assigment is pending IANA approval. 835 14. Contributing Author Information 837 Giles Heron 838 Tellabs 839 Abbey Place 840 24-28 Easton Street 841 High Wycombe 842 Bucks 843 HP11 1NT 844 UK 845 e-mail: giles.heron@tellabs.com 847 Dimitri Stratton Vlachos 848 Mazu Networks, Inc. 849 125 Cambridgepark Drive 850 Cambridge, MA 02140 851 e-mail: d@mazunetworks.com 853 Dan Tappan 854 Cisco Systems, Inc. 855 250 Apollo Drive 856 Chelmsford, MA, 01824 857 e-mail: tappan@cisco.com 858 Jayakumar Jayakumar, 859 Cisco Systems Inc. 860 225, E.Tasman, MS-SJ3/3, 861 San Jose, CA, 95134 862 e-mail: jjayakum@cisco.com 864 Alex Hamilton, 865 Cisco Systems Inc. 866 285 W. Tasman, MS-SJCI/3/4, 867 San Jose, CA, 95134 868 e-mail: tahamilt@cisco.com 870 Steve Vogelsang 871 Laurel Networks, Inc. 872 Omega Corporate Center 873 1300 Omega Drive 874 Pittsburgh, PA 15205 875 e-mail: sjv@laurelnetworks.com 877 John Shirron 878 Laurel Networks, Inc. 879 Omega Corporate Center 880 1300 Omega Drive 881 Pittsburgh, PA 15205 882 e-mail: jshirron@laurelnetworks.com 884 Toby Smith 885 Network Appliance, Inc. 886 800 Cranberry Woods Drive 887 Suite 300 888 Cranberry Township, PA 16066 889 e-mail: tob@netapp.com 891 Andrew G. Malis 892 Tellabs 893 90 Rio Robles Dr. 894 San Jose, CA 95134 895 e-mail: Andy.Malis@tellabs.com 896 Vinai Sirkay 897 Reliance Infocomm 898 Dhirubai Ambani Knowledge City 899 Navi Mumbai 400 709 900 India 901 e-mail: vinai@sirkay.com 903 Vasile Radoaca 904 Nortel Networks 905 600 Technology Park 906 Billerica MA 01821 907 e-mail: vasile@nortelnetworks.com 909 Chris Liljenstolpe 910 Alcatel 911 11600 Sallie Mae Dr. 912 9th Floor 913 Reston, VA 20193 914 e-mail: chris.liljenstolpe@alcatel.com 916 Dave Cooper 917 Global Crossing 918 960 Hamlin Court 919 Sunnyvale, CA 94089 920 e-mail: dcooper@gblx.net 922 Kireeti Kompella 923 Juniper Networks 924 1194 N. Mathilda Ave 925 Sunnyvale, CA 94089 926 e-mail: kireeti@juniper.net 928 15. Author Information 930 Luca Martini 931 Cisco Systems, Inc. 932 9155 East Nichols Avenue, Suite 400 933 Englewood, CO, 80112 934 e-mail: lmartini@cisco.com 935 Nasser El-Aawar 936 Level 3 Communications, LLC. 937 1025 Eldorado Blvd. 938 Broomfield, CO, 80021 939 e-mail: nna@level3.net 941 Eric Rosen 942 Cisco Systems, Inc. 943 250 Apollo Drive 944 Chelmsford, MA, 01824 945 e-mail: erosen@cisco.com