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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 This document and it's contents have been since superseded by the Pseudo Wire Edge to Edge Working Group specifications: [RFC4447], [RFC4385], [RFC4448], [ATM], [RFC4618], [RFC4619], [RFC4553], [CEP] and related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 protocol [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. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (September 2006) is 6432 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references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4447 (Obsoleted by RFC 8077) == Outdated reference: A later version (-14) exists of draft-ietf-pwe3-sonet-11 == Outdated reference: A later version (-11) exists of draft-ietf-pwe3-atm-encap-10 == Outdated reference: A later version (-19) exists of draft-martini-l2circuit-trans-mpls-18 ** Downref: Normative reference to an Historic draft: draft-martini-l2circuit-trans-mpls (ref. '1') -- Possible downref: Non-RFC (?) normative reference: ref. '3' -- Possible downref: Non-RFC (?) normative reference: ref. '4' -- Possible downref: Non-RFC (?) normative reference: ref. '5' Summary: 6 errors (**), 0 flaws (~~), 6 warnings (==), 10 comments (--). 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 Encapsulation Methods for Transport of Layer 2 Frames Over MPLS Networks 13 draft-martini-l2circuit-encap-mpls-12.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 encapsulating the Protocol Data 40 Units (PDUs) of layer 2 protocols such as Frame Relay, ATM, or 41 Ethernet for transport across an MPLS network. 43 Table of Contents 45 1 Specification of Requirements .......................... 3 46 2 Special Note ........................................... 3 47 3 Co-authors ............................................. 3 48 4 Introduction ........................................... 4 49 5 General encapsulation method ........................... 5 50 5.1 The Control Word ....................................... 5 51 5.1.1 Setting the sequence number ............................ 6 52 5.1.2 Processing the sequence number ......................... 6 53 5.2 MTU Requirements ....................................... 7 54 6 Protocol-Specific Details .............................. 8 55 6.1 Frame Relay ............................................ 8 56 6.2 ATM .................................................... 9 57 6.2.1 ATM AAL5 CPCS-SDU Mode ................................. 9 58 6.2.2 ATM Cell Mode .......................................... 11 59 6.2.3 OAM Cell Support ....................................... 12 60 6.2.4 CLP bit to Quality of Service mapping .................. 13 61 6.3 Ethernet VLAN .......................................... 13 62 6.4 Ethernet ............................................... 13 63 6.5 HDLC ................................................... 14 64 6.6 PPP .................................................... 14 65 7 Using an MPLS Label as the Demultiplexer Field ......... 14 66 7.1 MPLS Shim EXP Bit Values ............................... 15 67 7.2 MPLS Shim S Bit Value .................................. 15 68 7.3 MPLS Shim TTL Values ................................... 15 69 8 Security Considerations ................................ 15 70 9 IANA Considerations .................................... 15 71 10 Full Copyright Statement ............................... 15 72 11 Intellectual Property Statement ........................ 16 73 12 Normative References ................................... 16 74 13 Informative References ................................. 17 75 14 Co-Author Information .................................. 17 76 15 Author Information ..................................... 20 78 1. Specification of Requirements 80 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 81 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 82 document are to be interpreted as described in RFC 2119. 84 2. Special Note 86 This document describes the so called "draft-martini" protocol with 87 is used in many deployed implementations. This document and it's 88 contents have been since superseded by the Pseudo Wire Edge to Edge 89 Working Group specifications: [RFC4447], [RFC4385], [RFC4448], [ATM], 90 [RFC4618], [RFC4619], [RFC4553], [CEP] and related documents. This 91 document serves as a documentation of current implementations, and 92 MUST not be used for new implementations. The PWE3 LDP control 93 protocol [RFC4447] document, which is backward compatible with this 94 document MUST be used for all new implementations of this protocol. 96 3. Co-authors 98 The following are also co-authors of this document: 100 Daniel Tappan Cisco Systems 101 Kireeti Kompella Juniper Networks, Inc. 102 Steve Vogelsang Laurel Networks, Inc. 103 John Shirron Laurel Networks, Inc. 104 Vinai Sirkay Redback Networks 105 Giles Heron Tellabs 106 Andrew G. Malis Tellabs 107 Dimitri Stratton Vlachos Mazu Networks,Inc. 108 Chris Liljenstolpe Alcatel 109 Toby Smith Network Appliance. Inc. 110 Jayakumar Jayakumar Cisco Systems Inc. 111 Alex Hamilton Cisco Systems Inc. 112 Vasile Radoaca Nortel Networks 113 Dave Cooper Global Crossing 115 4. Introduction 117 In an MPLS network, it is possible to use control protocols such as 118 those specified in [1] to set up "emulated virtual circuits" that 119 carry the the Protocol Data Units of layer 2 protocols across the 120 network. A number of these emulated virtual circuits may be carried 121 in a single tunnel. This requires of course that the layer 2 PDUs be 122 encapsulated. We can distinguish three layers of this encapsulation: 124 - the "tunnel header", which contains the information needed to 125 transport the PDU across the MPLS network; this is header belongs 126 to the tunneling protocol, e.g., MPLS, GRE, L2TP. 128 - the "demultiplexer field", which is used to distinguish 129 individual emulated virtual circuits within a single tunnel; this 130 field must be understood by the tunneling protocol as well; it 131 may be, e.g., an MPLS label or a GRE key field. 133 - the "emulated VC encapsulation", which contains the information 134 about the enclosed layer 2 PDU which is necessary in order to 135 properly emulate the corresponding layer 2 protocol. 137 This document specifies the emulated VC encapsulation for a number of 138 layer 2 protocols. Although different layer 2 protocols require 139 different information to be carried in this encapsulation, an attempt 140 has been made to make the encapsulation as common as possible for all 141 layer 2 protocols. 143 This document also specifies the way in which the demultiplexer field 144 is added to the emulated VC encapsulation when an MPLS label is used 145 as the demultiplexer field. 147 QoS related issues are not discussed in this draft. 149 For the purpose of this document R1 will be defined as the ingress 150 router, and R2 as the egress router. A layer 2 PDU will be received 151 at R1, encapsulated at R1, transported, decapsulated at R2, and 152 transmitted out of R2. 154 5. General encapsulation method 156 In most cases, it is not necessary to transport the layer 2 157 encapsulation across the network; rather, the layer 2 header can be 158 stripped at R1, and reproduced at R2. This is done using information 159 carried in the control word (see below), as well as information that 160 may already have been signaled from R1 to R2. 162 5.1. The Control Word 164 There are three requirements that may need to be satisfied when 165 transporting layer 2 protocols over an MPLS backbone: 167 -i. Sequentiality may need to be preserved. 168 -ii. Small packets may need to be padded in order to be 169 transmitted on a medium where the minimum transport unit is 170 larger than the actual packet size. 171 -iii. Control bits carried in the header of the layer 2 frame may 172 need to be transported. 174 The control word defined here addresses all three of these 175 requirements. For some protocols this word is REQUIRED, and for 176 others OPTIONAL. For protocols where the control word is OPTIONAL 177 implementations MUST support sending no control word, and MAY support 178 sending a control word. 180 In all cases the egress router must be aware of whether the ingress 181 router will send a control word over a specific virtual circuit. 182 This may be achieved by configuration of the routers, or by 183 signaling, for example as defined in [1]. 185 The control word is defined as follows: 187 0 1 2 3 188 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 1 189 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 190 | Rsvd | Flags |0 0| Length | Sequence Number | 191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 193 In the above diagram the first 4 bits are reserved for future use. 194 They MUST be set to 0 when transmitting, and MUST be ignored upon 195 receipt. 197 The next 4 bits provide space for carrying protocol specific flags. 198 These are defined in the protocol-specific details below. 200 The next 2 bits MUST be set to 0 when transmitting. 202 The next 6 bits provide a length field, which is used as follows: If 203 the packet's length (defined as the length of the layer 2 payload 204 plus the length of the control word) is less than 64 bytes, the 205 length field MUST be set to the packet's length. Otherwise the length 206 field MUST be set to zero. The value of the length field, if non- 207 zero, can be used to remove any padding. When the packet reaches the 208 service provider's egress router, it may be desirable to remove the 209 padding before forwarding the packet. 211 The next 16 bits provide a sequence number that can be used to 212 guarantee ordered packet delivery. The processing of the sequence 213 number field is OPTIONAL. 215 The sequence number space is a 16 bit, unsigned circular space. The 216 sequence number value 0 is used to indicate an unsequenced packet. 218 5.1.1. Setting the sequence number 220 For a given emulated VC, and a pair of routers R1 and R2, if R1 221 supports packet sequencing then the following procedures should be 222 used: 224 - the initial packet transmitted on the emulated VC MUST use 225 sequence number 1 226 - subsequent packets MUST increment the sequence number by one for 227 each packet 228 - when the transmit sequence number reaches the maximum 16 bit 229 value (65535) the sequence number MUST wrap to 1 231 If the transmitting router R1 does not support sequence number 232 processing, then the sequence number field in the control word MUST 233 be set to 0. 235 5.1.2. Processing the sequence number 237 If a router R2 supports receive sequence number processing, then the 238 following procedures should be used: 240 When an emulated VC is initially set up, the "expected sequence 241 number" associated with it MUST be initialized to 1. 243 When a packet is received on that emulated VC, the sequence number 244 should be processed as follows: 246 - if the sequence number on the packet is 0, then the packet passes 247 the sequence number check 249 - otherwise if the packet sequence number >= the expected sequence 250 number and the packet sequence number - the expected sequence 251 number < 32768, then the packet is in order. 253 - otherwise if the packet sequence number < the expected sequence 254 number and the expected sequence number - the packet sequence 255 number >= 32768, then the packet is in order. 257 - otherwise the packet is out of order. 259 If a packet passes the sequence number check, or is in order then, it 260 can be delivered immediately. If the packet is in order, then the 261 expected sequence number should be set using the algorithm: 263 expected_sequence_number := packet_sequence_number + 1 mod 2**16 264 if (expected_sequence_number = 0) then expected_sequence_number := 1; 266 Packets which are received out of order MAY be dropped or reordered 267 at the discretion of the receiver. 269 If a router R2 does not support receive sequence number processing, 270 then the sequence number field MAY be ignored. 272 5.2. MTU Requirements 274 The network MUST be configured with an MTU that is sufficient to 275 transport the largest encapsulation frames. If MPLS is used as the 276 tunneling protocol, for example, this is likely to be 12 or more 277 bytes greater than the largest frame size. Other tunneling protocols 278 may have longer headers and require larger MTUs. If the ingress 279 router determines that an encapsulated layer 2 PDU exceeds the MTU of 280 the tunnel through which it must be sent, the PDU MUST be dropped. If 281 an egress router receives an encapsulated layer 2 PDU whose payload 282 length (i.e., the length of the PDU itself without any of the 283 encapsulation headers), exceeds the MTU of the destination layer 2 284 interface, the PDU MUST be dropped. 286 6. Protocol-Specific Details 288 6.1. Frame Relay 290 A Frame Relay PDU is transported without the Frame Relay header or 291 the FCS. The control word is REQUIRED; however, its use is optional, 292 although desirable. Use of the control word means that the ingress 293 and egress LSRs follow the procedures below. If an ingress LSR 294 chooses not to use the control word, it MUST set the flags in the 295 control word to 0; if an egress LSR chooses to ignore the control 296 word, it MUST set the Frame Relay control bits to 0. 298 The BECN, FECN, DE and C/R bits are carried across the network in the 299 control word. The edge routers that implement this document MAY, when 300 either adding or removing the encapsulation described herein, change 301 the BECN and/or FECN bits from zero to one in order to reflect 302 congestion in the network that is known to the edge routers, and the 303 D/E bit from zero to one to reflect marking from edge policing of the 304 Frame Relay Committed Information Rate. The BECN, FECN, and D/E bits 305 SHOULD NOT be changed from one to zero. 307 The following is an example of a Frame Relay packet: 309 0 1 2 3 310 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 1 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 | Rsvd |B|F|D|C| Length | Sequence Number | 313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 314 | Frame Relay PDU | 315 | " | 316 | " | 317 | " | 318 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 320 * B ( BECN ) Bit 322 The ingress router, R1, SHOULD copy the BECN field from the 323 incoming Frame Relay header into this field. The egress router, 324 R2, MUST generate a new BECN field based on the value of the B 325 bit. 327 * F ( FECN ) Bit 329 The ingress router, R1, SHOULD copy the FECN field from the 330 incoming Frame Relay header into this field. The egress router, 331 R2, MUST generate a new FECN field based on the value of the F 332 bit. 334 * D ( DE ) Bit 336 The ingress router, R1, SHOULD copy the DE field from the 337 incoming Frame Relay header into this field. The egress router, 338 R2, MUST generate a new DE field based on the value of the D bit. 340 If the tunneling protocol provides a field which can be set to 341 specify a Quality of Service, the ingress router, R1, MAY 342 consider the DE bit of the Frame Relay header when determining 343 the value of that field. The egress router MAY then consider the 344 value of this field when queuing the layer 2 PDU for egress. 345 Note however that frames from the same VC MUST NOT be reordered. 347 * C ( C/R ) Bit 349 The ingress router, R1, SHOULD copy the C/R bit from the received 350 Frame Relay PDU to the C bit of the control word. The egress 351 router, R2, MUST copy the C bit into the output frame. 353 6.2. ATM 355 Two encapsulations are supported for ATM transport: one for ATM AAL5 356 and another for ATM cells. 358 The AAL5 CPCS-SDU encapsulation consists of the REQUIRED control 359 word, and the AAL5 CPCS-SDU. The ATM cell encapsulation consists of 360 an OPTIONAL control word, a 4 byte ATM cell header, and the ATM cell 361 payload. 363 6.2.1. ATM AAL5 CPCS-SDU Mode 365 In ATM AAL5 mode the ingress router is required to reassemble AAL5 366 CPCS-SDUs from the incoming VC and transport each CPCS-SDU as a 367 single packet. No AAL5 trailer is transported. The control word is 368 REQUIRED; its use, however, is optional, although desirable. Use of 369 the control word means that the ingress and egress LSRs follow the 370 procedures below. If an ingress LSR chooses not to use the control 371 word, it MUST set the flags in the control word to 0; if an egress 372 LSR chooses to ignore the control word, it MUST set the ATM control 373 bits to 0. 375 The EFCI and CLP bits are carried across the network in the control 376 word. The edge routers that implement this document MAY, when either 377 adding or removing the encapsulation described herein, change the 378 EFCI bit from zero to one in order to reflect congestion in the 379 network that is known to the edge routers, and the CLP bit from zero 380 to one to reflect marking from edge policing of the ATM Sustained 381 Cell Rate. The EFCI and CLP bits MUST NOT be changed from one to 382 zero. 384 The AAL5 CPCS-SDU is prepended by the following header: 386 0 1 2 3 387 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 1 388 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 389 | Rsvd |T|E|L|C| Length | Sequence Number | 390 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 391 | ATM AAL5 CPCS-SDU | 392 | " | 393 | " | 394 | " | 395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 397 * T (transport type) bit 399 Bit (T) of the control word indicates whether the packet contains 400 an ATM cell or an AAL5 CPCS-SDU. If set the packet contains an 401 ATM cell, encapsulated according to the ATM cell mode section 402 below, otherwise it contains an AAL5 CPCS-SDU. The ability to 403 transport an ATM cell in the AAL5 mode is intended to provide a 404 means of enabling OAM functionality over the AAL5 VC. 406 * E ( EFCI ) Bit 408 The ingress router, R1, SHOULD set this bit to 1 if the EFCI bit 409 of the final cell of those that transported the AAL5 CPCS-SDU is 410 set to 1, or if the EFCI bit of the single ATM cell to be 411 transported in the packet is set to 1. Otherwise this bit SHOULD 412 be set to 0. The egress router, R2, SHOULD set the EFCI bit of 413 all cells that transport the AAL5 CPCS-SDU to the value contained 414 in this field. 416 * L ( CLP ) Bit 418 The ingress router, R1, SHOULD set this bit to 1 if the CLP bit 419 of any of the ATM cells that transported the AAL5 CPCS-SDU is set 420 to 1, or if the CLP bit of the single ATM cell to be transported 421 in the packet is set to 1. Otherwise this bit SHOULD be set to 422 0. The egress router, R2, SHOULD set the CLP bit of all cells 423 that transport the AAL5 CPCS-SDU to the value contained in this 424 field. 426 * C ( Command / Response Field ) Bit 428 When FRF.8.1 Frame Relay / ATM PVC Service Interworking [3] 429 traffic is being transported, the CPCS-UU Least Significant Bit 430 (LSB) of the AAL5 CPCS-SDU may contain the Frame Relay C/R bit. 431 The ingress router, R1, SHOULD copy this bit to the C bit of the 432 control word. The egress router, R2, SHOULD copy the C bit to the 433 CPCS-UU Least Significant Bit (LSB) of the AAL5 CPCS PDU. 435 6.2.2. ATM Cell Mode 437 In this encapsulation mode ATM cells are transported individually 438 without a SAR process. The ATM cell encapsulation consists of an 439 OPTIONAL control word, and one or more ATM cells - each consisting of 440 a 4 byte ATM cell header and the 48 byte ATM cell payload. This ATM 441 cell header is defined as in the FAST encapsulation [4] section 442 3.1.1, but without the trailer byte. The length of each frame, 443 without the encapsulation headers, is a multiple of 52 bytes long. 444 The maximum number of ATM cells that can be fitted in a frame, in 445 this fashion, is limited only by the network MTU and by the ability 446 of the egress router to process them. The ingress router MUST NOT 447 send more cells than the egress router is willing to receive. The 448 number of cells that the egress router is willing to receive may 449 either be configured in the ingress router or may be signaled, for 450 example using the methods described in [1]. The number of cells 451 encapsulated in a particular frame can be inferred by the frame 452 length. The control word is OPTIONAL. If the control word is used 453 then the flag bits in the control word are not used, and MUST be set 454 to 0 when transmitting, and MUST be ignored upon receipt. 456 The EFCI and CLP bits are carried across the network in the ATM cell 457 header. The edge routers that implement this document MAY, when 458 either adding or removing the encapsulation described herein, change 459 the EFCI bit from zero to one in order to reflect congestion in the 460 network that is known to the edge router, and the CLP bit from zero 461 to one to reflect marking from edge policing of the ATM Sustained 462 Cell Rate. The EFCI and CLP bits SHOULD NOT be changed from one to 463 zero. 465 This diagram illustrates an encapsulation of two ATM cells: 467 0 1 2 3 468 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 1 469 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 470 | Control word ( Optional ) | 471 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 472 | VPI | VCI | PTI |C| 473 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 474 | ATM Payload ( 48 bytes ) | 475 | " | 476 | " | 477 | " | 478 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 479 | VPI | VCI | PTI |C| 480 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 481 | ATM Payload ( 48 bytes ) | 482 | " | 483 | " | 484 | " | 485 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 487 * VPI 489 The ingress router MUST copy the VPI field from the incoming cell 490 into this field. For particular emulated VCs, the egress router 491 MAY generate a new VPI and ignore the VPI contained in this 492 field. 494 * VCI 496 The ingress router MUST copy the VCI field from the incoming ATM 497 cell header into this field. For particular emulated VCs, the 498 egress router MAY generate a new VCI. 500 * PTI & CLP ( C bit ) 502 The PTI and CLP fields are the PTI and CLP fields of the incoming 503 ATM cells. The cell headers of the cells within the packet are 504 the ATM headers (without HEC) of the incoming cell. 506 6.2.3. OAM Cell Support 508 OAM cells MAY be transported on the VC LSP. An egress router that 509 does not support transport of OAM cells MUST discard frames that 510 contain an ATM cell with the high-order bit of the PTI field set to 511 1. A router that supports transport of OAM cells MUST follow the 512 procedures outlined in [4] section 8 for mode 0 only, in addition to 513 the applicable procedures specified in [1]. 515 6.2.4. CLP bit to Quality of Service mapping 517 The ingress router MAY consider the CLP bit when determining the 518 value to be placed in the Quality of Service fields (e.g. the EXP 519 fields of the MPLS label stack) of the encapsulating protocol. This 520 gives the network visibility of the CLP bit. Note however that cells 521 from the same VC MUST NOT be reordered. 523 6.3. Ethernet VLAN 525 For an Ethernet 802.1q VLAN the entire Ethernet frame without the 526 preamble or FCS is transported as a single packet. The control word 527 is OPTIONAL. If the control word is used then the flag bits in the 528 control word are not used, and MUST be set to 0 when transmitting, 529 and MUST be ignored upon receipt. The 4 byte VLAN tag is transported 530 as is, and MAY be overwritten by the egress router. 532 The ingress router MAY consider the user priority field [5] of the 533 VLAN tag header when determining the value to be placed in the 534 Quality of Service field of the encapsulating protocol (e.g., the EXP 535 fields of the MPLS label stack). In a similar way, the egress router 536 MAY consider the Quality of Service field of the encapsulating 537 protocol when queuing the packet for egress. Ethernet packets 538 containing hardware level CRC errors, framing errors, or runt packets 539 MUST be discarded on input. 541 6.4. Ethernet 543 For simple Ethernet port to port transport, the entire Ethernet frame 544 without the preamble or FCS is transported as a single packet. The 545 control word is OPTIONAL. If the control word is used then the flag 546 bits in the control word are not used, and MUST be set to 0 when 547 transmitting, and MUST be ignored upon receipt. As in the Ethernet 548 VLAN case, Ethernet packets with hardware level CRC errors, framing 549 errors, and runt packets MUST be discarded on input. 551 6.5. HDLC 553 HDLC mode provides port to port transport of HDLC encapsulated 554 traffic. The HDLC PDU is transported in its entirety, including the 555 HDLC address, control and protocol fields, but excluding HDLC flags 556 and the FCS. Bit/Byte stuffing is undone. The control word is 557 OPTIONAL. If the control word is used then the flag bits in the 558 control word are not used, and MUST be set to 0 when transmitting, 559 and MUST be ignored upon receipt. 561 The HDLC mode is suitable for port to port transport of Frame Relay 562 UNI or NNI traffic. It must be noted, however, that this mode is 563 transparent to the FECN, BECN and DE bits. 565 6.6. PPP 567 PPP mode provides point to point transport of PPP encapsulated 568 traffic, as specified in [6]. The PPP PDU is transported in its 569 entirety, including the protocol field (whether compressed using PFC 570 or not), but excluding any media-specific framing information, such 571 as HDLC address and control fields or FCS. Since media-specific 572 framing is not carried the following options will not operate 573 correctly if the PPP peers attempt to negotiate them: 575 - Frame Check Sequence (FCS) Alternatives 576 - Address-and-Control-Field-Compression (ACFC) 577 - Asynchronous-Control-Character-Map (ACCM) 579 Note also that VC LSP Interface MTU negotiation as specified in [1] 580 is not affected by PPP MRU advertisement. Thus if a PPP peer sends a 581 PDU with a length in excess of that negotiated for the VC LSP that 582 PDU will be discarded by the ingress router. 584 The control word is OPTIONAL. If the control word is used then the 585 flag bits in the control word are not used, and MUST be set to 0 when 586 transmitting, and MUST be ignored upon receipt. 588 7. Using an MPLS Label as the Demultiplexer Field 590 To use an MPLS label as the demultiplexer field, a 32-bit label stack 591 entry [2] is simply prepended to the emulated VC encapsulation, and 592 hence will appear as the bottom label of an MPLS label stack. This 593 label may be called the "VC label". The particular emulated VC 594 identified by a particular label value must be agreed by the ingress 595 and egress LSRs, either by signaling (e.g, via the methods of [1]) or 596 by configuration. Other fields of the label stack entry are set as 597 follows. 599 7.1. MPLS Shim EXP Bit Values 601 If it is desired to carry Quality of Service information, the Quality 602 of Service information SHOULD be represented in the EXP field of the 603 VC label. If more than one MPLS label is imposed by the ingress LSR, 604 the EXP field of any labels higher in the stack SHOULD also carry the 605 same value. 607 7.2. MPLS Shim S Bit Value 609 The ingress LSR, R1, MUST set the S bit of the VC label to a value of 610 1 to denote that the VC label is at the bottom of the stack. 612 7.3. MPLS Shim TTL Values 614 The ingress LSR, R1, SHOULD set the TTL field of the VC label to a 615 value of 2. 617 8. Security Considerations 619 This document specifies only encapsulations, and not the protocols 620 used to carry the encapsulated packets across the network. Each such 621 protocol may have its own set of security issues, but those issues 622 are not affected by the encapsulations specified herein. 624 9. IANA Considerations 626 This document has no IANA Actions. 628 10. Full Copyright Statement 630 Copyright (C) The Internet Society (2006). 632 This document is subject to the rights, licenses and restrictions 633 contained in BCP 78, and except as set forth therein, the authors 634 retain all their rights. 636 This document and the information contained herein are provided on an 637 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 638 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 639 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 640 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 641 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 642 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 644 11. Intellectual Property Statement 646 The IETF takes no position regarding the validity or scope of any 647 Intellectual Property Rights or other rights that might be claimed to 648 pertain to the implementation or use of the technology described in 649 this document or the extent to which any license under such rights 650 might or might not be available; nor does it represent that it has 651 made any independent effort to identify any such rights. 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Normative References 670 [RFC4447] "Pseudowire Setup and Maintenance using LDP", 671 Martini, L., et al., RFC4447,April 2006. 673 [RFC4385] "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word 674 for Use over an MPLS PSN", RFC4385, February 2006. 676 [CEP] "SONET/SDH Circuit Emulation Service Over Packet (CEP)", 677 draft-ietf-pwe3-sonet-11.txt (work in progress) 679 [RFC4553] "Structure-Agnostic TDM over Packet (SAToP)", RFC4553, 680 June 2006. 682 [RFC4619] "Frame Relay over Pseudo-Wires", RFC4619, August 2006. 684 [ATM] "Encapsulation Methods for Transport of ATM Over MPLS 685 Networks", draft-ietf-pwe3-atm-encap-10.txt (work in progress) 687 [RFC4618] "Encapsulation Methods for Transport of PPP/HDLC Frames 688 MPLS Networks", RFC4618, August 2006 690 [RFC4448] "Encapsulation Methods for Transport of Ethernet Frames 691 Over MPLS Networks", RFC4448, April 2006. 693 [1] "Transport of Layer 2 Frames Over MPLS", 694 draft-martini-l2circuit-trans-mpls-18.txt. ( work in progress ) 696 [2] "MPLS Label Stack Encoding", E. Rosen, Y. Rekhter, D. Tappan, G. 697 Fedorkow, D. Farinacci, T. Li, A. Conta. RFC3032 699 [3] "Frame Relay / ATM PVC Service Interworking Implementation 700 Agreement", Frame Relay Forum 2000. 702 [4] "Frame Based ATM over SONET/SDH Transport (FAST)," 2000. 704 [5] "IEEE 802.3ac-1998" IEEE standard specification. 706 13. Informative References 708 [6] "The Point-to-Point Protocol (PPP)", RFC 1661. 710 14. Co-Author Information 712 Giles Heron 713 Tellabs 714 Abbey Place 715 24-28 Easton Street 716 High Wycombe 717 Bucks 718 HP11 1NT 719 UK 720 e-mail: giles.heron@tellabs.com 722 Dimitri Stratton Vlachos 723 Mazu Networks, Inc. 724 125 Cambridgepark Drive 725 Cambridge, MA 02140 726 e-mail: d@mazunetworks.com 727 Dan Tappan 728 Cisco Systems, Inc. 729 1414 Massachusetts Avenue 730 Boxborough, MA 01719 731 e-mail: tappan@cisco.com 733 Jayakumar Jayakumar, 734 Cisco Systems Inc. 735 225, E.Tasman, MS-SJ3/3, 736 San Jose, CA, 95134 737 e-mail: jjayakum@cisco.com 739 Alex Hamilton, 740 Cisco Systems Inc. 741 285 W. Tasman, MS-SJCI/3/4, 742 San Jose, CA, 95134 743 e-mail: tahamilt@cisco.com 745 Steve Vogelsang 746 Laurel Networks, Inc. 747 Omega Corporate Center 748 1300 Omega Drive 749 Pittsburgh, PA 15205 750 e-mail: sjv@laurelnetworks.com 752 John Shirron 753 Laurel Networks, Inc. 754 Omega Corporate Center 755 1300 Omega Drive 756 Pittsburgh, PA 15205 757 e-mail: jshirron@laurelnetworks.com 759 Toby Smith 760 Network Appliance, Inc. 761 800 Cranberry Woods Drive 762 Suite 300 763 Cranberry Township, PA 16066 764 e-mail: tob@netapp.com 765 Andrew G. Malis 766 Tellabs 767 90 Rio Robles Dr. 768 San Jose, CA 95134 769 e-mail: Andy.Malis@tellabs.com 771 Vinai Sirkay 772 Redback Networks 773 300 Holger Way 774 San Jose, CA 95134 775 e-mail: vsirkay@redback.com 777 Vasile Radoaca 778 Nortel Networks 779 600 Technology Park 780 Billerica MA 01821 781 e-mail: vasile@nortelnetworks.com 783 Chris Liljenstolpe 784 Alcatel 785 11600 Sallie Mae Dr. 786 9th Floor 787 Reston, VA 20193 788 e-mail: chris.liljenstolpe@alcatel.com 790 Dave Cooper 791 Global Crossing 792 960 Hamlin Court 793 Sunnyvale, CA 94089 794 e-mail: dcooper@gblx.net 796 Kireeti Kompella 797 Juniper Networks 798 1194 N. Mathilda Ave 799 Sunnyvale, CA 94089 800 e-mail: kireeti@juniper.net 802 15. Author Information 804 Luca Martini 805 Cisco Systems, Inc. 806 9155 East Nichols Avenue, Suite 400 807 Englewood, CO, 80112 808 e-mail: lmartini@cisco.com 810 Nasser El-Aawar 811 Level 3 Communications, LLC. 812 1025 Eldorado Blvd. 813 Broomfield, CO, 80021 814 e-mail: nna@level3.net 816 Eric Rosen 817 Cisco Systems, Inc. 818 1414 Massachusetts Avenue 819 Boxborough, MA 01719 820 e-mail: erosen@cisco.com