idnits 2.17.1 draft-ietf-pwe3-control-protocol-03.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** Looks like you're using RFC 2026 boilerplate. This must be updated to follow RFC 3978/3979, as updated by RFC 4748. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- == No 'Intended status' indicated for this document; assuming Proposed Standard Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) ** The document seems to lack separate sections for Informative/Normative References. All references will be assumed normative when checking for downward references. Miscellaneous warnings: ---------------------------------------------------------------------------- == Line 249 has weird spacing: '...re also proto...' == Line 476 has weird spacing: '... The highe...' == Line 477 has weird spacing: '...resence of a...' == Line 561 has weird spacing: '...sist of an At...' == Line 564 has weird spacing: '...ntifier may b...' == (2 more instances...) == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: The PW FEC TLV SHOULD not include the interface parameters as they are ignored in the context of this message. When a PE's CE-facing interface encounters an error, use of the PW status message allows the PE to send a single status message, using a PW FEC TLV with only the group ID set, to denote this change in status for all affected PW connections. -- 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. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (June 2003) is 7620 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC3036' is mentioned on line 124, but not defined ** Obsolete undefined reference: RFC 3036 (Obsoleted by RFC 5036) == Missing Reference: 'LDP' is mentioned on line 672, but not defined == Missing Reference: '32768' is mentioned on line 983, but not defined == Unused Reference: '4' is defined on line 1022, but no explicit reference was found in the text == Unused Reference: 'RFC2434' is defined on line 1058, but no explicit reference was found in the text ** Obsolete normative reference: RFC 3036 (ref. '1') (Obsoleted by RFC 5036) -- Possible downref: Non-RFC (?) normative reference: ref. '2' -- Possible downref: Non-RFC (?) normative reference: ref. '4' -- Possible downref: Non-RFC (?) normative reference: ref. '5' -- Possible downref: Non-RFC (?) normative reference: ref. '6' == Outdated reference: A later version (-07) exists of draft-ietf-pwe3-frame-relay-01 == Outdated reference: A later version (-14) exists of draft-ietf-pwe3-sonet-01 -- Possible downref: Non-RFC (?) normative reference: ref. '9' == Outdated reference: A later version (-11) exists of draft-ietf-pwe3-atm-encap-02 -- No information found for draft-ietf-pwe3-hdlc-ppp-encap - is the name correct? -- Possible downref: Normative reference to a draft: ref. '11' == Outdated reference: A later version (-11) exists of draft-ietf-pwe3-ethernet-encap-01 == Outdated reference: A later version (-07) exists of draft-ietf-pwe3-arch-04 ** Downref: Normative reference to an Informational draft: draft-ietf-pwe3-arch (ref. '13') == Outdated reference: A later version (-15) exists of draft-ietf-pwe3-iana-allocation-01 ** Obsolete normative reference: RFC 2434 (Obsoleted by RFC 5226) Summary: 7 errors (**), 0 flaws (~~), 19 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Luca Martini 3 Internet Draft Nasser El-Aawar 4 Expiration Date: December 2003 Level 3 Communications, LLC. 6 Toby Smith Eric C. Rosen 7 Laurel Networks, Inc. Cisco Systems, Inc. 8 Giles Heron 9 PacketExchange Ltd. 11 June 2003 13 Pseudowire Setup and Maintenance using LDP 15 draft-ietf-pwe3-control-protocol-03.txt 17 Status of this Memo 19 This document is an Internet-Draft and is in full conformance with 20 all provisions of Section 10 of RFC2026. 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/ietf/1id-abstracts.txt. 34 The list of Internet-Draft Shadow Directories can be accessed at 35 http://www.ietf.org/shadow.html. 37 Abstract 39 Layer 2 services (such as Frame Relay, ATM, ethernet) can be 40 "emulated" over an IP and/or MPLS backbone by encapsulating the layer 41 2 PDUs and then transmitting them over "pseudowires". It is also 42 possible to use pseudowires to provide SONET circuit emulation over 43 an IP and/or MPLS network. This document specifies a protocol for 44 establishing and maintaining the pseudowires, using extensions to 45 LDP. Procedures for encapsulating layer 2 PDUs are specified in a 46 set of companion documents. 48 Table of Contents 50 1 Specification of Requirements .......................... 3 51 2 Introduction ........................................... 3 52 3 The Pseudowire Label ................................... 5 53 4 Details Specific to Particular Emulated Services ....... 6 54 4.1 Frame Relay ............................................ 6 55 4.2 ATM .................................................... 6 56 4.2.1 ATM AAL5 SDU VCC Transport ............................. 6 57 4.2.2 ATM Transparent Cell Transport ......................... 7 58 4.2.3 ATM n-to-one VCC and VPC Cell Transport ................ 7 59 4.2.4 OAM Cell Support ....................................... 7 60 4.2.5 ILMI Support ........................................... 8 61 4.2.6 ATM AAL5 PDU VCC Transport ............................. 9 62 4.2.7 ATM one-to-one VCC and VPC Cell Transport .............. 9 63 4.3 Ethernet VLAN .......................................... 9 64 4.4 Ethernet ............................................... 9 65 4.5 HDLC and PPP ........................................... 10 66 4.6 IP Layer2 Transport .................................... 10 67 5 LDP .................................................... 10 68 5.1 The PWid FEC Element ................................... 11 69 5.2 The Generalized ID FEC Element ......................... 12 70 5.2.1 Attachment Identifiers ................................. 13 71 5.2.2 Encoding the Generalized ID FEC Element ................ 14 72 5.2.3 Procedures ............................................. 15 73 5.3 Signaling of Pseudo Wire Status ........................ 16 74 5.3.1 Use of Label Mappings. ................................. 16 75 5.3.2 Signaling PW status. ................................... 16 76 5.4 Interface Parameters Field ............................. 17 77 5.4.1 PW types for which the control word is REQUIRED ........ 19 78 5.4.2 PW types for which the control word is NOT mandatory ... 20 79 5.4.3 Status codes ........................................... 21 80 5.5 LDP label Withdrawal procedures ........................ 21 81 5.6 Sequencing Considerations .............................. 22 82 5.6.1 Label Mapping Advertisements ........................... 22 83 5.6.2 Label Mapping Release .................................. 23 84 6 Security Considerations ................................ 23 85 7 References ............................................. 23 86 8 Author Information ..................................... 24 87 9 Additional Contributing Authors ........................ 25 88 10 Appendix A - C-bit Handling Procedures Diagram ......... 28 90 1. Specification of Requirements 92 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 93 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 94 document are to be interpreted as described in RFC 2119. 96 2. Introduction 98 In [7], [10], and [12] it is explained how to encapsulate a layer 2 99 Protocol Data Unit (PDU) for transmission over an IP and/or MPLS 100 network. Those specifications that a "pseudowire header", consisting 101 of a demultiplexor field, will be prepended to the encapsulated PDU. 102 The pseudowire demultiplexor field is put on before transmitting a 103 packet on a pseudowire. When the packet arrives at the remote 104 endpoint of the pseudowire, the demultiplexor is what enables the 105 receiver to identify the particular pseudowire on which the packet 106 has arrived. To actually transmit the packet from one pseudowire 107 endpoint to another, the packet may need to travel through a "PSN 108 tunnel"; this will require an additional header to be prepended to 109 the packet. 111 An accompanying document [8] also describes a method for transporting 112 time division multiplexed (TDM) digital signals (TDM circuit 113 emulation) over a packet-oriented MPLS network. The transmission 114 system for circuit-oriented TDM signals is the Synchronous Optical 115 Network (SONET)[5]/Synchronous Digital Hierarchy (SDH) [6]. To 116 support TDM traffic, which includes voice, data, and private leased 117 line service, the pseudowires must emulate the circuit 118 characteristics of SONET/SDH payloads. The TDM signals and payloads 119 are encapsulated for transmission over pseudowires. To this 120 encapsulation is prepended a pseudowire demultiplexor and a PSN 121 tunnel header. 123 In this document, we specify the use of the MPLS Label Distribution 124 Protocol, LDP [RFC3036], as a protocol a protocol for setting up and 125 maintaining the pseudowires. In particular, we define new TLVs for 126 LDP, which enable LDP to identify pseudowires and to signal 127 attributes of pseudowires. We specify how a pseudowire endpoint uses 128 these TLVs in LDP to bind a demultiplexor field value to a 129 pseudowire, and how it informs the remote endpoint of the binding. 130 We also specify procedures for reporting pseudowire status changes, 131 passing additional information about the pseudowire as needed, and 132 for releasing the bindings. 134 In the protocol specified herein, the pseudowire demultiplexor field 135 is an MPLS label. Thus the packets which are transmitted from one 136 end of the pseudowire to the other are MPLS packets. Unless the 137 pseudowire endpoints are immediately adjacent, these MPLS packets 138 must be transmitted through a PSN tunnel. Any sort of PSN tunnel can 139 be used, as long as it is possible to transmit MPLS packets through 140 it. The PSN tunnel can itself be an LSP, but it could equally well 141 be an IP tunnel, a GRE tunnel, an IPsec tunnel, or any other sort of 142 tunnel which can carry MPLS packets. Procedures for setting up and 143 maintaining the PSN tunnels are outside the scope of this document. 145 This document deals only with the setup and maintenance of point-to- 146 point pseudowires. Neither point-to-multipoint nor multipoint-to- 147 point pseudowires are discussed. 149 QoS related issues are not discussed in this document. 151 The following two figures describe the reference models which are 152 derived from [13] to support the Ethernet PW emulated services. 154 Native |<----- Pseudo Wire ---->| Native 155 Layer2 | | Layer2 156 Service | |<-- PSN Tunnel -->| | Service 157 | V V V V | 158 | +----+ +----+ | 159 +----+ | | PE1|==================| PE2| | +----+ 160 | |----------|............PW1.............|----------| | 161 | CE1| | | | | | | |CE2 | 162 | |----------|............PW2.............|----------| | 163 +----+ | | |==================| | | +----+ 164 ^ +----+ +----+ | ^ 165 | Provider Edge 1 Provider Edge 2 | 166 | | 167 |<-------------- Emulated Service ---------------->| 169 Figure 1: PWE3 Reference Model 171 +-------------+ +-------------+ 172 | Layer2 | | Layer2 | 173 | Emulated | | Emulated | 174 | Services | Emulated Service | Services | 175 | |<==============================>| | 176 +-------------+ Pseudo Wire +-------------+ 177 |Demultiplexor|<==============================>|Demultiplexor| 178 +-------------+ +-------------+ 179 | PSN | PSN Tunnel | PSN | 180 | MPLS |<==============================>| MPLS | 181 +-------------+ +-------------+ 182 | Physical | | Physical | 183 +-----+-------+ +-----+-------+ 185 Figure 2: PWE3 Protocol Stack Reference Model 187 For the purpose of this document, PE1 will be defined as the ingress 188 router, and PE2 as the egress router. A layer 2 PDU will be received 189 at PE1, encapsulated at PE1, transported, decapsulated at PE2, and 190 transmitted out of PE2. 192 3. The Pseudowire Label 194 Suppose it is desired to transport layer 2 PDUs from ingress LSR PE1 195 to egress LSR PE2, across an intervening PSN. We assume that there is 196 a PSN tunnel from PE1 to PE2. That is, we assume that PE1 can cause a 197 packet to be delivered to PE2 by encapsulating the packet in a "PSN 198 tunnel header" and sending the result to one of its adjacencies. If 199 the PSN tunnel is an MPLS Label Switched Path (LSP), then putting on 200 a PSN tunnel encapsulation is a matter of pushing on an additional 201 MPLS label; if the PSN tunnel is, e.g., a GRE tunnel, then putting on 202 the tunnel encapsulation requires prepending an IP header and a GRE 203 header. 205 We presuppose that an arbitrary number of pseudowires can be carried 206 through a single PSN tunnel. Thus it is never necessary to maintain 207 state in the network core for individual pseudowires. We do not 208 presuppose that the PSN tunnels are point-to-point; although the 209 pseudowires are point-to-point, the PSN tunnels may be multipoint- 210 to-point. We do not presuppose that PE2 will even be able to 211 determine the PSN tunnel through which a received packet was 212 transmitted. (E.g., if the PSN tunnel is an LSP, and penultimate hop 213 popping is used, when the packet arrives at PE2 it will contain no 214 information identifying the tunnel.) 216 When PE2 receives a packet over a pseudowire, it must be able to 217 determine that the packet was in fact received over a pseudowire, and 218 it must be able to associate that packet with a particular 219 pseudowire. PE2 is able to do this by examining the MPLS label which 220 serves as the pseudowire demultiplexor field shown in Figure 2. Call 221 this label the "PW label". 223 So when PE1 sends a layer 2 PDU to PE2, it first pushes a PW label on 224 its label stack, thereby creating an MPLS packet. It then (if PE1 is 225 not adjacent to PE2) encapsulates that MPLS packet in a PSN tunnel 226 header. (If the PSN tunnel is an LSP, this is just a matter of 227 pushing on a second label.) The PW label is not visible again until 228 the MPLS packet reaches PE2. PE2's disposition of the packet is based 229 on the PW label. 231 Note that the PW label must always be at the bottom of the packet's 232 label stack and labels MUST be allocated from the per-platform label 233 space. 235 This document specifies a protocol for assigning and distributing the 236 PW label. This protocol is LDP, extended as specified in the 237 remainder of this document. An LDP session must be set up between 238 the pseudowire endpoints. LDP MUST be used in its "downstream 239 unsolicited" mode. LDP's "liberal label retention" mode SHOULD be 240 used. 242 In addition to the protocol specified herein, static assignment of PW 243 labels MAY be used, and implementations of this protocol SHOULD 244 provide support for static assignment. 246 This document specifies all the procedures necessary to set up and 247 maintain the pseudowires needed to support "unswitched" point-to- 248 point services, where each endpoint of the pseudowire is provisioned 249 with the identify of the other endpoint. There are also protocol 250 mechanisms specified herein which can be used to support switched 251 services, and which can be used to support other provisioning models. 252 However, the use of the protocol mechanisms to support those other 253 models and services is not described in this document. 255 4. Details Specific to Particular Emulated Services 257 4.1. Frame Relay 259 When emulating a frame relay service, the Frame Relay PDUs are 260 encapsulated according to the procedures defined in [7]. The PE MUST 261 provide Frame Relay PVC status signaling to the Frame Relay network. 262 If the PE detects a service affecting condition for a particular 263 DLCI, as defined in [2] Q.933 Annex A.5 sited in IA FRF1.1, PE MUST 264 communicate to the remote PE the status of the PW corresponds to the 265 frame relay DLCI. The Egress PE SHOULD generate the corresponding 266 errors and alarms as defined in [2] on the egress Frame relay PVC. 268 4.2. ATM 270 4.2.1. ATM AAL5 SDU VCC Transport 272 ATM AAL5 CSPS-SDUs are encapsulated according to [10] ATM AAL5 CPCS- 273 SDU mode. This mode allows the transport of ATM AAL5 CSPS-SDUs 274 traveling on a particular ATM PVC across the network to another ATM 275 PVC. 277 4.2.2. ATM Transparent Cell Transport 279 This mode is similar to the Ethernet port mode. Every cell that is 280 received at the ingress ATM port on the ingress PE, PE1, is 281 encapsulated according to [10], ATM cell mode n-to-one, and sent 282 across the PW to the egress PE, PE2. This mode allows an ATM port to 283 be connected to only one other ATM port. [10] ATM cell n-to-one mode 284 allows for concatenation ( grouping ) of multiple cells into a single 285 MPLS frame. Concatenation of ATM cells is OPTIONAL for transmission 286 at the ingress PE, PE1. If the Egress PE PE2 supports cell 287 concatenation the ingress PE, PE1, should only concatenate cells up 288 to the "Maximum Number of concatenated ATM cells" parameter received 289 as part of the FEC element. 291 4.2.3. ATM n-to-one VCC and VPC Cell Transport 293 This mode is similar to the ATM AAL5 VCC transport except that cells 294 are transported. Every cell that is received on a pre-defined ATM 295 PVC, or ATM PVP, at the ingress ATM port on the ingress PE, PE1, is 296 encapsulated according to [10], ATM n-to-one cell mode, and sent 297 across the LSP to the egress PE PE2. Grouping of ATM cells is 298 OPTIONAL for transmission at the ingress PE, PE1. If the Egress PE 299 PE2 supports cell concatenation the ingress PE, PE1, MUST only 300 concatenate cells up to the "Maximum Number of concatenated ATM cells 301 in a frame" parameter received as part of the FEC element. 303 4.2.4. OAM Cell Support 305 OAM cells MAY be transported on the VC LSP. When the PE is operating 306 in AAL5 CPCS-SDU transport mode if it does not support transport of 307 ATM cells, the PE MUST discard incoming MPLS frames on an ATM PW LSP 308 that contain a PW label with the T bit set [10]. When operating in 309 AAL5 SDU transport mode an PE that supports transport of OAM cells 310 using the T bit defined in [10], or an PE operating in any of the 311 cell transport modes MUST follow the procedures outlined in [9] 312 section 8 for mode 0 only, in addition to the applicable procedures 313 specified in [6]. 315 4.2.4.1. SDU/PDU OAM Cell Emulation Mode 317 A PE operating in ATM SDU, or PDU transport mode, that does not 318 support transport of OAM cells across an LSP MAY provide OAM support 319 on ATM PVCs using the following procedures: 321 - Loopback cells response 323 If an F5 end-to-end OAM cell is received from a ATM VC, by either 324 PE that is transporting this ATM VC, with a loopback indication 325 value of 1, and the PE has a label mapping for the ATM VC, then 326 the PE MUST decrement the loopback indication value and loop back 327 the cell on the ATM VC. Otherwise the loopback cell MUST be 328 discarded by the PE. 330 - AIS Alarm. 332 If an ingress PE, PE1, receives an AIS F4/F5 OAM cell, it MUST 333 notify the remote PE of the failure. The remote PE , PE2, MUST in 334 turn send F5 OAM AIS cells on the respective PVCs. Note that is 335 the PE supports forwarding of OAM cells, then the received OAM 336 AIS alarm cells MUTS be forwarded along the PW as well. 338 - Interface failure. 340 If the PE detects a physical interface failure, or the interface 341 is administratively disabled, the PE MUST notify the remote PE 342 for all VCs associated with the failure. 344 - PSN/PW failure detection. 346 If the PE detects a failure in the PW, by receiving a label 347 withdraw for a specific PW ID, or the targeted LDP session fails, 348 or a PW status TLV notification is received, then a propper AIS 349 F5 OAM cell MUST be generated for all the affected atm PVCs. The 350 AIS OAM alarm will be generated on the ATM output port of the PE 351 that detected the failure. 353 4.2.5. ILMI Support 355 An MPLS edge PE MAY provide an ATM ILMI to the ATM edge switch. If an 356 ingress PE receives an ILMI message indicating that the ATM edge 357 switch has deleted a VC, or if the physical interface goes down, it 358 MUST send a PW status notification message for all PWs associated 359 with the failure. When a PW label mapping is withdrawn, or PW status 360 notification message is received the egress PE SHOULD notify its 361 client of this failure by deleting the VC using ILMI. 363 4.2.6. ATM AAL5 PDU VCC Transport 365 ATM AAL5 CSPS-PDUs are encapsulated according to [10] ATM AAL5 CPCS- 366 PDU mode. This mode allows the transport of ATM AAL5 CSPS-PDUs 367 traveling on a particular ATM PVC across the network to another ATM 368 PVC. This mode supports fragmentation of the ATM AAL5 CPCS-PDU in 369 order to maintain the position of the OAM cells with respect to the 370 user cells. Fragmentation may also be performed to maintain the size 371 of the packet carrying the AAL5 PDU within the MTU of the link. 373 4.2.7. ATM one-to-one VCC and VPC Cell Transport 375 This mode is similar to the ATM AAL5 n-to-one cell transport except 376 an encapsulation method that maps one ATM VCC or one ATM VPC to one 377 Pseudo-Wire is used. Every cell that is received on a pre-defined ATM 378 PVC, or ATM PVP, at the ingress ATM port on the ingress PE, PE1, is 379 encapsulated according to [10], ATM one-to-one cell mode, and sent 380 across the LSP to the egress PE PE2. Grouping of ATM cells is 381 OPTIONAL for transmission at the ingress PE, PE1. If the Egress PE 382 PE2 supports cell concatenation the ingress PE, PE1, MUST only 383 concatenate cells up to the "Maximum Number of concatenated ATM cells 384 in a frame" parameter received as part of the FEC element. 386 4.3. Ethernet VLAN 388 The Ethernet frame will be encapsulated according to the procedures 389 in [12] tagged mode. It should be noted that if the VLAN identifier 390 is modified by the egress PE, according to the procedures outlined 391 above, the Ethernet spanning tree protocol might fail to work 392 properly. If the PE detects a failure on the Ethernet physical port, 393 or the port is administratively disabled, it MUST send PW status 394 notification message for all PWs associated with the port. This mode 395 uses service-delimiting tags to map input ethernet frames to 396 respective PWs. 398 4.4. Ethernet 400 The Ethernet frame will be encapsulated according to the procedures 401 in [12] "ethernet raw mode". If the PE detects a failure on the 402 Ethernet input port, or the port is administratively disabled, the PE 403 MUST send a corresponding PW status notification message. 405 4.5. HDLC and PPP 407 HDLC and PPP frames are encapsulated according to the procedures in 408 [11]. If the MPLS edge PE detects that the physical link has failed, 409 or the port is administratively disabled, it MUST send a PW status 410 notification message that corresponds to the HDLC or PPP PW. 412 4.6. IP Layer2 Transport 414 This mode switches IP packets into a Peudo-Wire. the encapsulation 415 used is according to [3]. IP interworking is implementation specific, 416 part of the NSP function [13], and is outside the scope of this 417 document. 419 5. LDP 421 The PW label bindings are distributed using the LDP downstream 422 unsolicited mode described in [1]. The PEs will establish an LDP 423 session using the Extended Discovery mechanism described in [1, 424 section 2.4.2 and 2.5]. 426 An LDP Label Mapping message contains a FEC TLV, a Label TLV, and 427 zero or more optional parameter TLVs. 429 The FEC TLV is used to indicate the meaning of the label. In the 430 current context, the FEC TLV would be used to identify the particular 431 pseudowire that a particular label is bound to. In this 432 specification, we define two new FEC TLVs to be used for identifying 433 pseudowires. When setting up a particular pseudowire, only one of 434 these FEC TLVs is used. The one to be used will depend on the 435 particular service being emulated and on the particular provisioning 436 model being supported. 438 LDP allows each FEC TLV to consist of a set of FEC elements. For 439 setting up and maintaining pseudowires, however, each FEC TLV MUST 440 contain exactly one FEC element. 442 LDP has several kinds of label TLVs. For setting up and maintaining 443 pseudowires, the Generic Label TLV MUST be used. 445 5.1. The PWid FEC Element 447 The PWid FEC element may be used whenever both pseudowire endpoints 448 have been provisioned with the same 32-bit identifier for the 449 pseudowire. 451 For this purpose a new type of FEC element is defined. The FEC 452 element type is 128 [note1], and is defined as follows: 454 0 1 2 3 455 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 1 456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 457 | PW tlv |C| PW type |PW info Length | 458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 459 | Group ID | 460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 461 | PW ID | 462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 463 | Interface parameters | 464 | " | 465 | " | 466 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 468 - PW type 470 A 15 bit quantity containing a value which represents the type of 471 PW. Assigned Values are specified in "IANA Allocations for pseudo 472 Wire Edge to Edge Emulation (PWE3)" [14]. 474 - Control word bit (C) 476 The highest order bit (C) of the PW type is used to flag the 477 presence of a control word ( defined in [7] ) as follows: 479 bit 15 = 1 control word present on this VC. 480 bit 15 = 0 no control word present on this VC. 482 Please see the section "C-Bit Handling Procedures" for further 483 explanation. 485 - PW information length 487 Length of the PW ID field and the interface parameters field in 488 octets. If this value is 0, then it references all PWs using the 489 specified group ID and there is no PW ID present, nor any 490 interface parameters. 492 - Group ID 494 An arbitrary 32 bit value which represents a group of PWs that is 495 used to create groups in the VC space. The group ID is intended 496 to be used as a port index, or a virtual tunnel index. To 497 simplify configuration a particular PW ID at ingress could be 498 part of the virtual tunnel for transport to the egress router. 499 The Group ID is very useful to send wild card label withdrawals, 500 or PW wild card status notification messages to remote PEs upon 501 physical port failure. 503 - PW ID 505 A non-zero 32-bit connection ID that together with the PW type, 506 identifies a particular PW. Note that the PW ID and the PW type 507 must be the same at both endpoints. 509 - Interface parameters 511 This variable length field is used to provide interface specific 512 parameters, such as CE-facing interface MTU. 514 Note that as the "interface parameters" are part of the FEC, the 515 rules of LDP make it impossible to change the interface 516 parameters once the pseudowire has been set up. Thus the 517 interface parameters field must not be used to pass information, 518 such as status information, which may change during the life of 519 the pseudowire. Optional parameter TLVs should be used for that 520 purpose. 522 Using the PWid FEC, each of the two pseudowire endpoints 523 independently initiates the set up of a unidirectional LSP. An 524 outgoing LSP and an incoming LSP are bound together into a single 525 pseudowire if they have the same PW ID and PW type. 527 5.2. The Generalized ID FEC Element 529 There are cases where the PWid FEC element cannot be used, because 530 both endpoints have not been provisioned with a common 32-bit PWid. 531 In such cases, the "Generalized ID FEC Element" is used instead. 532 This is FEC type 129 (provisionally, subject to assignment by IANA). 533 It differs from the PWid FEC element in that the PWid and the group 534 id are eliminated, and their place is taken by a generalized 535 identifier field as described below. The Generalized ID FEC element 536 includes a PW type field, a C bit, and an interface parameters field; 537 these three fields are identical to those in the PWid FEC, and are 538 used as discussed in the previous section. 540 5.2.1. Attachment Identifiers 542 As discussed in [13], a pseudowire can be thought of as connecting 543 two "forwarders". The protocol used to setup a pseudowire must allow 544 the forwarder at one end of a pseudowire to identify the forwarder at 545 the other end. We use the term "attachment identifier", or "AI", to 546 refer to the field which the protocol uses to identify the 547 forwarders. In the PWid FEC, the PWid field serves as the AI. In 548 this section we specify a more general form of AI which is structured 549 and of variable length. 551 Every Forwarder in a PE must be associated with an Attachment 552 Identifier (AI), either through configuration or through some 553 algorithm. The Attachment Identifier must be unique in the context 554 of the PE router in which the Forwarder resides. The combination must be globally unique. 557 It is frequently convenient to a set of Forwarders as being members 558 of a particular "group", where PWs may only be set up among members 559 of a group. In such cases, it is convenient to identify the 560 Forwarders relative to the group, so that an Attachment Identifier 561 would consist of an Attachment Group Identifier (AGI) plus an 562 Attachment Individual Identifier (AII). 564 An Attachment Group Identifier may be thought of as a VPN-id, or 565 a VLAN identifier, some attribute which is shared by all the 566 Attachment VCs (or pools thereof) which are allowed to be connected. 568 The details of how to construct the AGI and AII fields identifying 569 the pseudowire endpoints are outside the scope of this specification. 570 Different pseudowire application, and different provisioning models, 571 will require different sorts of AGI and AII fields. The 572 specification of each such application and/or model must include the 573 rules for constructing the AGI and AII fields. 575 As previously discussed, a (bidirectional) pseudowire consists of a 576 pair of unidirectional LSPs, one in each direction. If a particular 577 pseudowire connects PE1 with PE2, the LSP in the PE1-->PE2 direction 578 can be identified as: 580 , PE2, >, 582 and the LSP in the PE2--PE1 direction can be identified by: 584 , PE1, >. 586 Note that the AGI must be the same at both endpoints, but the AII 587 will in general be different at each endpoint. Thus from the 588 perspective of a particular PE, each pseudowire has a local or 589 "Source AII", and a remote or "Target AII". The pseudowire setup 590 protocol can carry all three of these quantities: 592 - Attachment Group Identifier (AGI). 594 - Source Attachment Individual Identifier (SAII) 596 - Target Attachment Individual Identifier (TAII) 598 If the AGI is non-null, then the Source AI (SAI) consists of the AGI 599 together with the SAII, and the Target AI (TAI) consists of the TAII 600 together with the AGI. If the AGI is null, then the SAII and TAII 601 are the SAI and TAI respectively. 603 The interpretation of the SAI and TAI is a local matter at the 604 respective endpoint. 606 The association of two unidirectional LSPs into a single 607 bidirectional pseudowire depends on the SAI and the TAI. Each 608 application and/or provisioning model which uses the Generalized ID 609 FEC element must specify the rules for performing this association. 611 5.2.2. Encoding the Generalized ID FEC Element 613 FEC element type 129 is used. The FEC element is encoded as 614 follows: 616 0 1 2 3 617 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 1 618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 619 | 129 |C| PW Type |VC info Length | 620 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 621 | Parameters | 622 | " | 623 | " | 624 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 626 additional Parameters are: 628 - SAII, encoded as a one byte length field followed by the SAII. 630 - TAII, encoded as a one byte length field followed by the TAII. 632 - AGI, encoded as a one byte length field followed by the AGI. 634 The SAII, TAII, and AGI are simply carried as octet strings. The 635 length byte specifies the size of the field, excluding the length 636 byte itself. The null string can be sent by setting the length 637 byte to 0. 639 5.2.3. Procedures 641 In order for PE1 to begin signaling PE2, PE1 must know the address of 642 the remote PE2, and a TAI. This information may have been configured 643 at PE1, or it may have been learned dynamically via some 644 autodiscovery procedure. 646 To begin the signaling procedure, a PE (PE1) that has knowledge of 647 the other endpoint (PE2) initiates the setup of the LSP in the 648 incoming (PE2-->PE1) direction by sending a Label Mapping message 649 containing the FEC type 129. The FEC element includes the SAII, AGI, 650 and TAII. 652 What happens when PE2 receives such a Label Mapping message? 654 PE2 interprets the message as a request to set up a PW whose endpoint 655 (at PE2) is the Forwarder identified by the TAI. From the 656 perspective of the signaling protocol, exactly how PE2 maps AIs to 657 Forwarders is a local matter. In some VPWS provisioning models, the 658 TAI might, e.g., be a string which identifies a particular Attachment 659 Circuit, such as "ATM3VPI4VCI5", or it might, e.g., be a string such 660 as "Fred" which is associated by configuration with a particular 661 Attachment Circuit. In VPLS, the TAI would be a VPN-id, identifying 662 a particular VPLS instance. 664 If PE2 cannot map the TAI to one of its Forwarders, then PE2 sends a 665 Label Release message to PE1, with a Status Code meaning "invalid 666 TAI", and the processing of the Mapping message is complete. 668 If the Label Mapping Message has a valid TAI, PE2 must decide whether 669 to accept it or not. The procedures for so deciding will depend on 670 the particular type of Forwarder identified by the TAI. Of course, 671 the Label Mapping message may be rejected due to standard LDP error 672 conditions as detailed in [LDP]. 674 If PE2 decides to accept the Label Mapping message, then it has to 675 make sure that an LSP is set up in the opposite (PE1-->PE2) 676 direction. If it has already signaled for the corresponding LSP in 677 that direction, nothing more need be done. Otherwise, it must 678 initiate such signaling by sending a Label Mapping message to PE1. 679 This is very similar to the Label Mapping message PE2 received, but 680 with the SAI and TAI reversed. 682 5.3. Signaling of Pseudo Wire Status 684 5.3.1. Use of Label Mappings. 686 The PEs MUST send PW label mapping messages to their peers as soon as 687 the PW is configured and administratively enabled, regardless of the 688 CE-facing interface state. The PW label should not be withdrawn 689 unless the user administratively configures the CE-facing interface 690 down (or the PW configuration is deleted entirely). A simple label 691 withdraw method MAY also be supported as an alternative. In any case 692 if the Label mapping is not available the PW MUST be considered in 693 the down state. 695 5.3.2. Signaling PW status. 697 The PE devices use an LDP TLV to indicate status to their remote 698 peers. This PW Status TLV contains more information than the 699 alternative simple Label Withdraw message. 701 The format of the PW Status TLV is: 702 0 1 2 3 703 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 1 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 705 |1|0| PW Status (0x0???) | Length | 706 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 707 | Status Code | 708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 710 Where status is a 4 octet bit field is specified in the PW IANA 711 Allocations document [14] 713 Each bit in the status code field can be set individually to indicate 714 more then a single failure at once. Each fault can be cleared by 715 sending an appropriate status message with the respective bit 716 cleared. The presence of the lowest bit (PW Not Forwarding) acts only 717 as a generic failure indication when there is a link-down event for 718 which none of the other bits apply. 720 The Status TLV is transported to the remote PW peer via the LDP 721 notification message. The format of the Notification Message is: 723 0 1 2 3 724 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 1 725 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 726 |0| Notification (0x0001) | Message Length | 727 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 728 | Message ID | 729 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 730 | PW FEC TLV or Generalized ID FEC Element | 731 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 732 | PW Status TLV | 733 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 735 The PW FEC TLV SHOULD not include the interface parameters as they 736 are ignored in the context of this message. When a PE's CE-facing 737 interface encounters an error, use of the PW status message allows 738 the PE to send a single status message, using a PW FEC TLV with only 739 the group ID set, to denote this change in status for all affected PW 740 connections. 742 As mentioned above the Group ID field can be used to send a status 743 notification for all PWs associated with a particular group ID. This 744 procedure is OPTIONAL, and if it is implemented the LDP Notification 745 message should be as follows: the PW information length field is set 746 to 0, the PW ID field is not present, and the interface parameters 747 field is not present. For the purpose of this document this is called 748 the "wild card PW status notification procedure", and all PEs 749 implementing this design are REQUIRED to accept such a notification 750 message, but are not required to send it. 752 5.4. Interface Parameters Field 754 This field specifies interface specific parameters. When applicable, 755 it MUST be used to validate that the PEs, and the ingress and egress 756 ports at the edges of the circuit, have the necessary capabilities to 757 interoperate with each other. The field structure is defined as 758 follows: 760 0 1 2 3 761 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 1 762 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 763 | Parameter ID | Length | Variable Length Value | 764 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 765 | Variable Length Value | 766 | " | 767 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 768 The parameter ID Values are specified in "IANA Allocations for pseudo 769 Wire Edge to Edge Emulation (PWE3)" [14]. 771 The Length field is defined as the length of the interface parameter 772 including the parameter id and length field itself. Processing of the 773 interface parameters should continue when encountering unknown 774 interface parameters and they MUST be silently ignored. 776 - Interface MTU 778 A 2 octet value indicating the MTU in octets. This is the Maximum 779 Transmission Unit, excluding encapsulation overhead, of the 780 egress packet interface that will be transmitting the 781 decapsulated PDU that is received from the MPLS network. This 782 parameter is applicable only to PW types 1, 2, 4, 5, 6, 7,14, and 783 15 and is REQUIRED for these PW types. If this parameter does not 784 match in both directions of a specific PW, that PW MUST NOT be 785 enabled. 787 - Maximum Number of concatenated ATM cells 789 A 2 octet value specifying the maximum number of concatenated ATM 790 cells that can be processed as a single PDU by the egress PE. An 791 ingress PE transmitting concatenated cells on this PW can 792 concatenate a number of cells up to the value of this parameter, 793 but MUST NOT exceed it. This parameter is applicable only to PW 794 types 3, 9, and 0x0a, and is REQUIRED for these PWC types. This 795 parameter does not need to match in both directions of a specific 796 PW. 798 - Optional Interface Description string 800 This arbitrary, OPTIONAL, interface description string is used to 801 send a human-readable administrative string describing the 802 interface to the remote. This parameter is OPTIONAL, and is 803 applicable to all PW types. The interface description parameter 804 string length is variable, and can be from 0 to 80 octets. 805 Human-readable text MUST be provided in the UTF-8 charset using 806 the Default Language [RFC2277]. 808 - Payload Bytes 810 A 2 octet value indicating the number of TDM payload octets 811 contained in all packets on the CEM stream, from 48 to 1,023 812 octets. All of the packets in a given CEM stream have the same 813 number of payload bytes. Note that there is a possibility that 814 the packet size may exceed the SPE size in the case of an STS-1 815 SPE, which could cause two pointers to be needed in the CEM 816 header, since the payload may contain two J1 bytes for 817 consecutive SPEs. For this reason, the number of payload bytes 818 must be less than or equal to 783 for STS-1 SPEs. 820 - CEP Options. 822 An optional 16 Bit value of CEM Flags. See [8] for the definition 823 of the bit values. 825 - Requested VLAN ID. 827 An Optional 16 bit value indicating the requested VLAN ID. This 828 parameter MAY be used by an PE that is incapable of rewriting the 829 802.1Q ethernet VLAN tag on output. If the ingress PE receives 830 this request it MAY rewrite the VLAN ID tag in input to match the 831 requested VLAN ID. If this is not possible, and the VLAN ID does 832 not already match configured ingress VLAN ID the PW should not be 833 enabled.This parameter is applicable only to PW type 4. 835 - CEP/TDM bit rate. 837 This 32-bit integer is mandatory for CEP. For other PWs carrying 838 TDM traffic it is mandatory if the bit-rate cannot be directly 839 inferred from the service type. If present, it expresses the bit 840 rate of the attachment circuit as known to the advertizing PE in 841 "units" of 64 kbit/s. I.e., the value 26 must be used for CEP 842 carrying VT1.5 SPE, 35 - for CEP carrying a VT2 SPE, 99 - for VT6 843 SPE, 783 - for STS-1 SPE and n*783 - for STS-nc, n = 3, 12, 48, 844 192. Attempts to establish a PWC between a pair of TDM ports 845 with different bit-rates MUST be rejected with the appropriate 846 status code (see section "Status codes" below). 848 - Frame-Relay DLCI lenth. 850 An optional 16 bit value indicating the lenght of the frame-relay 851 DLCI field. This OPTIONAL interface paremeter can have value of 2 852 , or 4, with the default being equal to 2. If this interface 853 parameter is not present the default value of 2 is assumed. 855 5.4.1. PW types for which the control word is REQUIRED 857 The Label Mapping messages which are sent in order to set up these 858 PWs MUST have c=1. When a Label Mapping message for a PW of one of 859 these types is received, and c=0, a Label Release MUST be sent, with 860 an "Illegal C-bit" status code. In this case, the PW will not be 861 enabled. 863 5.4.2. PW types for which the control word is NOT mandatory 865 If a system is capable of sending and receiving the control word on 866 PW types for which the control word is not mandatory, then each such 867 PW endpoint MUST be configurable with a parameter that specifies 868 whether the use of the control word is PREFERRED or NOT PREFERRED. 869 For each PW, there MUST be a default value of this parameter. This 870 specification does NOT state what the default value should be. 872 If a system is NOT capable of sending and receiving the control word 873 on PWC types for which the control word is not mandatory, then it 874 behaves as exactly as if it were configured for the use of the 875 control word to be NOT PREFERRED. 877 If a Label Mapping message for the PW has already been received, but 878 no Label Mapping message for the PW has yet been sent, then the 879 procedure is the following: 881 -i. If the received Label Mapping message has c=0, send a Label 882 Mapping message with c=0, and the control word is not used. 883 -ii. If the received Label Mapping message has c=1, and the PW is 884 locally configured such that the use of the control word is 885 preferred, then send a Label Mapping message with c=1, and 886 the control word is used. 887 -iii. If the received Label Mapping message has c=1, and the PW is 888 locally configured such that the use of the control word is 889 not preferred or the control word is not supported, then act 890 as if no Label Mapping message for the PW had been received 891 (i.e., proceed to the next paragraph). 893 If a Label Mapping message for the PW has not already been received 894 (or if the received Label Mapping message had c=1 and either local 895 configuration says that the use of the control word is not preferred 896 or the control word is not supported), then send a Label Mapping 897 message in which the c bit is set to correspond to the locally 898 configured preference for use of the control word. (I.e., set c=1 if 899 locally configured to prefer the control word, set c=0 if locally 900 configured to prefer not to use the control word or if the control 901 word is not supported). 903 The next action depends on what control message is next received for 904 that PW. The possibilities are: 906 -i. A Label Mapping message with the same c bit value as 907 specified in the Label Mapping message that was sent. PW 908 setup is now complete, and the control word is used if c=1 909 but not used if c=0. 911 -ii. A Label Mapping message with c=1, but the Label Mapping 912 message that was sent has c=0. In this case, ignore the 913 received Label Mapping message, and continue to wait for the 914 next control message for the PW. 915 -iii. A Label Mapping message with c=0, but the Label Mapping 916 message that was sent has c=1. In this case, send a Label 917 Withdraw message with a "Wrong c-bit" status code, followed 918 by a Label Mapping message that has c=0. PW setup is now 919 complete, and the control word is not used. 920 -iv. A Label Withdraw message with the "Wrong c-bit" status code. 921 Treat as a normal Label Withdraw, but do not respond. 922 Continue to wait for the next control message for the PW. 924 If at any time after a Label Mapping message has been received, a 925 corresponding Label Withdraw or Release is received, the action taken 926 is the same as for any Label Withdraw or Release that might be 927 received at any time. Note that receiving a Label Withdraw should not 928 cause a corresponding Label Release to be sent. 930 If both endpoints prefer the use of the control word, this procedure 931 will cause it to be used. If either endpoint prefers not to use the 932 control word, or does not support the control word, this procedure 933 will cause it not to be used. If one endpoint prefers to use the 934 control word but the other does not, the one that prefers not to use 935 it is has no extra protocol to execute, it just waits for a Label 936 Mapping message that has c=0. 938 The diagram in Appendix A illustrates the above procedure. 940 5.4.3. Status codes 942 RFC 3036 has a range of Status Code values which are assigned by IANA 943 on a First Come, First Served basis. These additional status codes, 944 and assigned Values are specified in "IANA Allocations for pseudo 945 Wire Edge to Edge Emulation (PWE3)" [14]. 947 5.5. LDP label Withdrawal procedures 949 As mentioned above the Group ID field can be used to withdraw all PW 950 labels associated with a particular group ID. This procedure is 951 OPTIONAL, and if it is implemented the LDP label withdraw message 952 should be as follows: the PW information length field is set to 0, 953 the PW ID field is not present, and the interface parameters field is 954 not present. For the purpose of this document this is called the 955 "wild card withdraw procedure", and all PEs implementing this design 956 are REQUIRED to accept such a withdraw message, but are not required 957 to send it. 959 The interface parameters field MUST NOT be present in any LDP PW 960 label withdrawal message or release message. A wildcard release 961 message MUST include only the group ID. A Label Release message 962 initiated from the imposition router must always include the PW ID. 964 5.6. Sequencing Considerations 966 In the case where the router considers the sequence number field in 967 the control word, it is important to note the following when 968 advertising labels 970 5.6.1. Label Mapping Advertisements 972 After a label has been withdrawn by the disposition router and/or 973 released by the imposition router, care must be taken to not re- 974 advertise (re-use) the released label until the disposition router 975 can be reasonably certain that old packets containing the released 976 label no longer persist in the MPLS network. 978 This precaution is required to prevent the imposition router from 979 restarting packet forwarding with sequence number of 1 when it 980 receives the same label mapping if there are still older packets 981 persisting in the network with sequence number between 1 and 32768. 982 For example, if there is a packet with sequence number=n where n is 983 in the interval[1,32768] traveling through the network, it would be 984 possible for the disposition router to receive that packet after it 985 re-advertises the label. Since the label has been released by the 986 imposition router, the disposition router SHOULD be expecting the 987 next packet to arrive with sequence number to be 1. Receipt of a 988 packet with sequence number equal to n will result in n packets 989 potentially being rejected by the disposition router until the 990 imposition router imposes a sequence number of n+1 into a packet. 991 Possible methods to avoid this is for the disposition router to 992 always advertise a different PW label, or for the disposition router 993 to wait for a sufficient time before attempting to re-advertised a 994 recently released label. This is only an issue when sequence number 995 processing at the disposition router is enabled. 997 5.6.2. Label Mapping Release 999 In situations where the imposition router wants to restart forwarding 1000 of packets with sequence number 1, the router shall 1) Send to 1001 disposition router a label mapping release, and 2) Send to 1002 disposition router a label mapping request. When sequencing is 1003 supported, advertisement of a PW label in response to a label mapping 1004 request MUST also consider the issues discussed in the section on 1005 Label Mapping Advertisements. 1007 6. Security Considerations 1009 This document does not affect the underlying security issues of MPLS. 1011 7. References 1013 [1] "LDP Specification." L. Andersson, P. Doolan, N. Feldman, A. 1014 Fredette, B. Thomas. January 2001. RFC3036 1016 [2] ITU-T Recommendation Q.933, and Q.922 Specification for Frame 1017 Mode Basic call control, ITU Geneva 1995 1019 [3] "MPLS Label Stack Encoding", E. Rosen, Y. Rekhter, D. Tappan, G. 1020 Fedorkow, D. Farinacci, T. Li, A. Conta. RFC3032 1022 [4] "IEEE 802.3ac-1998" IEEE standard specification. 1024 [5] American National Standards Institute, "Synchronous Optical 1025 Network Formats," ANSI T1.105-1995. 1027 [6] ITU Recommendation G.707, "Network Node Interface For The 1028 Synchronous Digital Hierarchy", 1996. 1030 [7] "Frame Relay over Pseudo-Wires", draft-ietf-pwe3-frame-relay- 1031 01.txt. ( work in progress ) 1033 [8] "SONET/SDH Circuit Emulation Service Over Packet (CEP)", 1034 draft-ietf-pwe3-sonet-01.txt ( Work in progress ) 1036 [9] ATM Forum Specification fb-fbatm-0151.000 (2000) ,Frame Based ATM 1037 over SONET/SDH Transport (FAST) 1039 [10] "Encapsulation Methods for Transport of ATM Cells/Frame Over IP 1040 and MPLS Networks", draft-ietf-pwe3-atm-encap-02.txt ( work in 1041 progress ) 1043 [11] "Encapsulation Methods for Transport of PPP/HDLC Frames Over IP 1044 and MPLS Networks", draft-ietf-pwe3-hdlc-ppp-encap-00.txt. ( work in 1045 progress ) 1047 [12] "Encapsulation Methods for Transport of Ethernet Frames Over 1048 IP/MPLS Networks", draft-ietf-pwe3-ethernet-encap-01.txt. ( work in 1049 progress ) 1051 [13] "PWE3 Architecture" Bryant, et al., draft-ietf-pwe3-arch-04.txt 1052 ( work in progress ), August 2003. 1054 [14] "IANA Allocations for pseudo Wire Edge to Edge Emulation (PWE3)" 1055 Martini, Townsley, draft-ietf-pwe3-iana-allocation-01.txt ( work in 1056 progress ), February 2003 1058 [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1059 IANA Considerations section in RFCs", BCP 26, RFC 2434, October 1998. 1061 [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and 1062 Languages", BCP 18, RFC 2277, January 1998. 1064 [note1] FEC element type 128 is pending IANA approval. 1066 [note2] Status codes assigment is pending IANA approval. 1068 8. Author Information 1070 Luca Martini 1071 Level 3 Communications, LLC. 1072 1025 Eldorado Blvd. 1073 Broomfield, CO, 80021 1074 e-mail: luca@level3.net 1076 Nasser El-Aawar 1077 Level 3 Communications, LLC. 1078 1025 Eldorado Blvd. 1079 Broomfield, CO, 80021 1080 e-mail: nna@level3.net 1081 Giles Heron 1082 PacketExchange Ltd. 1083 The Truman Brewery 1084 91 Brick Lane 1085 LONDON E1 6QL 1086 United Kingdom 1087 e-mail: giles@packetexchange.net 1089 Eric Rosen 1090 Cisco Systems, Inc. 1091 250 Apollo Drive 1092 Chelmsford, MA, 01824 1093 e-mail: erosen@cisco.com 1095 Dan Tappan 1096 Cisco Systems, Inc. 1097 250 Apollo Drive 1098 Chelmsford, MA, 01824 1099 e-mail: tappan@cisco.com 1101 9. Additional Contributing Authors 1103 Dimitri Stratton Vlachos 1104 Mazu Networks, Inc. 1105 125 Cambridgepark Drive 1106 Cambridge, MA 02140 1107 e-mail: d@mazunetworks.com 1109 Jayakumar Jayakumar, 1110 Cisco Systems Inc. 1111 225, E.Tasman, MS-SJ3/3, 1112 San Jose, CA, 95134 1113 e-mail: jjayakum@cisco.com 1115 Alex Hamilton, 1116 Cisco Systems Inc. 1117 285 W. Tasman, MS-SJCI/3/4, 1118 San Jose, CA, 95134 1119 e-mail: tahamilt@cisco.com 1120 Steve Vogelsang 1121 Laurel Networks, Inc. 1122 Omega Corporate Center 1123 1300 Omega Drive 1124 Pittsburgh, PA 15205 1125 e-mail: sjv@laurelnetworks.com 1127 John Shirron 1128 Omega Corporate Center 1129 1300 Omega Drive 1130 Pittsburgh, PA 15205 1131 Laurel Networks, Inc. 1132 e-mail: jshirron@laurelnetworks.com 1134 Toby Smith 1135 Omega Corporate Center 1136 1300 Omega Drive 1137 Pittsburgh, PA 15205 1138 Laurel Networks, Inc. 1139 e-mail: tob@laurelnetworks.com 1141 Andrew G. Malis 1142 Vivace Networks, Inc. 1143 2730 Orchard Parkway 1144 San Jose, CA 95134 1145 Phone: +1 408 383 7223 1146 Email: Andy.Malis@vivacenetworks.com 1148 Vinai Sirkay 1149 Vivace Networks, Inc. 1150 2730 Orchard Parkway 1151 San Jose, CA 95134 1152 e-mail: sirkay@technologist.com 1154 Vasile Radoaca 1155 Nortel Networks 1156 600 Technology Park 1157 Billerica MA 01821 1158 e-mail: vasile@nortelnetworks.com 1159 Chris Liljenstolpe 1160 Cable & Wireless 1161 11700 Plaza America Drive 1162 Reston, VA 20190 1163 e-mail: chris@cw.net 1165 Dave Cooper 1166 Global Crossing 1167 960 Hamlin Court 1168 Sunnyvale, CA 94089 1169 e-mail: dcooper@gblx.net 1171 Kireeti Kompella 1172 Juniper Networks 1173 1194 N. Mathilda Ave 1174 Sunnyvale, CA 94089 1175 e-mail: kireeti@juniper.net 1177 10. Appendix A - C-bit Handling Procedures Diagram 1179 ------------------ 1180 Y | Received Label | N 1181 -------| Mapping Msg? |-------------- 1182 | ------------------ | 1183 -------------- | 1184 | | | 1185 ------- ------- | 1186 | C=0 | | C=1 | | 1187 ------- ------- | 1188 | | | 1189 | ---------------- | 1190 | | Control Word | N | 1191 | | Capable? |----------- | 1192 | ---------------- | | 1193 | Y | | | 1194 | | | | 1195 | ---------------- | | 1196 | | Control Word | N | | 1197 | | Preferred? |---- | | 1198 | ---------------- | | | 1199 | Y | | | | 1200 | | | | ---------------- 1201 | | | | | Control Word | 1202 | | | | | Preferred? | 1203 | | | | ---------------- 1204 | | | | N | Y | 1205 | | | | | | 1206 Send Send Send Send Send Send 1207 C=0 C=1 C=0 C=0 C=0 C=1 1208 | | | | 1209 ---------------------------------- 1210 | If receive the same as sent, | 1211 | PW setup is complete. If not: | 1212 ---------------------------------- 1213 | | | | 1214 ------------------- ----------- 1215 | Receive | | Receive | 1216 | C=1 | | C=0 | 1217 ------------------- ----------- 1218 | | 1219 Wait for the Send 1220 next message Wrong C-Bit 1221 | 1222 Send Label 1223 Mapping Message