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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 MPLS WG A. Farrel 2 Internet Draft P. Brittain 3 Document: draft-brittain-mpls-ldp-ft-00.txt Data Connection Ltd 4 Expiration Date: January 2001 5 Philip Matthews 6 Nortel 8 Eric Gray 9 Zaffire 10 July 2000 12 Fault Tolerance for LDP and CR-LDP 14 Status of this Memo 16 This document is an Internet-Draft and is in full conformance with 17 all provisions of Section 10 of RFC2026 [1]. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. Internet-Drafts are draft documents valid for a maximum of 23 six months and may be updated, replaced, or obsoleted by other 24 documents at any time. It is inappropriate to use Internet- Drafts 25 as reference material or to cite them other than as "work in 26 progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 NOTE: The new TLV type numbers, bit values for flags specified in 35 this draft, and new LDP status code values are preliminary suggested 36 values and have yet to be approved by IANA or the MPLS WG. See the 37 section "IANA Considerations" for further details. 39 Abstract 41 MPLS systems will be used in core networks where system downtime 42 must be kept to an absolute minimum. Many MPLS LSRs may, therefore, 43 exploit fault tolerant (FT) hardware or software to provide 44 high availability of the core networks. 46 The details of how FT is achieved for the various components of an FT 47 LSR, including LDP, CR-LDP, the switching hardware and TCP, are 48 implementation specific. This document identifies issues in the 49 CR-LDP specification [2] and the LDP specification [4] that make it 50 difficult to implement an FT LSR using the current LDP and CR-LDP 51 protocols, and proposes enhancements to the LDP specification to ease 52 such FT LSR implementations. 54 The extensions described here are equally applicable to CR-LDP. 56 Contents 58 1. Conventions and Terminology used in this document...............3 59 2. Introduction....................................................3 60 2.1 Fault Tolerance for MPLS.......................................3 61 2.2 Issues with LDP and CR-LDP.....................................4 62 3. Overview of LDP FT Enhancements.................................5 63 3.1 Establishing an FT LDP Session.................................6 64 3.1.1 Interoperation with Non-FT LSRs.............................6 65 3.2 TCP Connection Failure.........................................6 66 3.3 Data Forwarding During TCP Connection Failure..................7 67 3.4 FT LDP Session Reconnection....................................7 68 3.5 Operations on FT Labels........................................8 69 4. FT Operations...................................................8 70 4.1 FT LDP Messages................................................8 71 4.1.1 FT Label Messages............................................8 72 4.1.1.1 Scope of FT Labels.........................................9 73 4.1.2 FT Address Messages.........................................9 74 4.2 FT Operation ACKs..............................................9 75 4.3 Preservation of FT State......................................10 76 4.4 FT Procedure After TCP Failure................................11 77 4.4.1 FT LDP Operations During TCP Failure........................12 78 4.5 FT Procedure After TCP Re-connection..........................12 79 4.5.1 Re-Issuing FT Messages......................................13 80 4.5.2 Interaction with CR-LDP LSP Modification....................13 81 5. Changes to Existing Messages...................................14 82 5.1 LDP Initialization Message....................................14 83 5.2 LDP Keepalive Message.........................................14 84 5.3 All Other LDP Session Messages................................14 85 6. New Fields and Values..........................................15 86 6.1 Status Codes..................................................15 87 6.2 FT Session TLV................................................16 88 6.3 FT Protection TLV.............................................17 89 6.4 FT ACK TLV....................................................18 90 7. Example Use....................................................19 91 8. Security Considerations........................................22 92 9. Implementation Notes...........................................22 93 9.1 FT Recovery Support on Non-FT LSRs............................22 94 9.2 ACK generation logic..........................................23 95 10. Acknowledgements..............................................23 96 11. Intellectual Property Consideration...........................23 97 12. Full Copyright Statement......................................24 98 13. IANA Considerations...........................................24 99 14. Authors' Addresses............................................26 100 15. References....................................................26 102 1. Conventions and Terminology used in this document 104 Definitions of key words and terms applicable to LDP and CR-LDP are 105 inherited from [2] and [4]. 107 The term "FT label" is introduced in this document to 108 indicated a label for which fault tolerant operation is used. A 109 "non-FT label" is not fault tolerant and is handled as specified in 110 [2] and [4]. 112 The extensions to LDP specified in this document are collectively 113 referred to as the "LDP FT enhancements". 115 In the examples quoted, the following notation is used. 117 Ln : An LSP. For example L1. 118 Pn : An LDP peer. For example P1. 120 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 121 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 122 this document are to be interpreted as described in RFC-2119 [3]. 124 2. Introduction 126 High Availability (HA) is typically claimed by equipment vendors 127 when their hardware achieves availability levels of at least 99.999% 128 (five 9s). To implement this, the equipment must be capable of 129 recovering from local hardware and software failures through a 130 process known as fault tolerance (FT). 132 The usual approach to FT involves provisioning backup copies of 133 hardware and software. When a primary copy fails, processing is 134 switched to the backup copy. This process, called failover, should 135 result in minimal disruption to the Data Plane. 137 In an FT system, backup resources are sometimes provisioned on a 138 one-to-one basis (1:1), sometimes as many-to-one (1:n), and 139 occasionally as many-to-many (m:n). Whatever backup provisioning is 140 made, the system must switch to the backup automatically on failure 141 of the primary, and the software and hardware state in the backup 142 must be set to replicate the state in the primary at the point 143 of failure. 145 2.1 Fault Tolerance for MPLS 147 MPLS systems will be used in core networks where system downtime must 148 be kept to an absolute minimum. Many MPLS LSRs may, therefore, 149 exploit FT hardware or software to provide high availability of core 150 networks. 152 In order to provide HA, an MPLS system needs to be able to survive 153 a variety of faults with minimal disruption to the Data Plane, 154 including the following fault types: 155 - failure/hot-swap of a physical connection between LSRs 156 - failure/hot-swap of the switching fabric in the LSR 157 - failure of the TCP or LDP stack in an LSR 158 - software upgrade to the TCP or LDP stacks. 160 The first two examples of faults listed above are confined to the 161 Data Plane. Such faults can be handled by providing redundancy in 162 the Data Plane which is transparent to LDP operating in the Control 163 Plane. The last two example types of fault require action in 164 the Control Plane to recover from the fault without disrupting 165 traffic in the Data Plane. This is possible because many recent 166 router architectures separate the Control and Data Planes such that 167 forwarding can continue unaffected by recovery action in the Control 168 Plane. 170 2.2 Issues with LDP and CR-LDP 172 LDP and CR-LDP use TCP to provide reliable connections between LSRs 173 over which to exchange protocol messages to distribute labels and to 174 set up LSPs. A pair of LSRs that have such a connection are referred 175 to as LDP peers. 177 TCP enables LDP and CR-LDP to assume reliable transfer of protocol 178 messages. This means that some of the messages do not need to be 179 acknowledged (for example, Label Release). 181 LDP and CR-LDP are defined such that if the TCP connection fails, the 182 LSR should immediately tear down the LSPs associated with the session 183 between the LDP peers, and release any labels and resources assigned 184 to those LSPs. 186 It is notoriously hard to provide a fault tolerant implementation of 187 TCP. To do so might involve making copies of all data sent and 188 received. This is an issue familiar to implementers of other TCP 189 applications such as BGP. 191 During failover affecting the TCP or LDP stacks, therefore, the TCP 192 connection may be lost. Recovery from this position is made worse by 193 the fact that LDP or CR-LDP control messages may have been lost 194 during the connection failure. Since these messages are unconfirmed, 195 it is possible that LSP or label state information will be lost. 197 This draft describes a solution which involves 198 - negotiation between LDP peers of the intent to support extensions 199 to LDP that facilitate recovery from failover without loss of LSPs 200 - selection of FT survival on a per LSP/label basis 201 - acknowledgement of LDP messages to ensure that a full handshake is 202 performed on those messages 203 - re-issuing lost messages after failover to ensure that LSP/label 204 state is correctly recovered after reconnection of the LDP session. 206 Other objectives of this draft are to 207 - offer back-compatibility with LSRs that do not implement these 208 proposals 209 - preserve existing protocol rules described in [2] and [4] for 210 handling unexpected duplicate messages and for processing 211 unexpected messages referring to unknown LSPs/labels 212 - integrate with the LSP modification function described in [5] 213 - avoid full state refresh solutions (such as those present in RSVP: 214 see [6], [7] and [8]) whether they be full-time, or limited to post- 215 failover recovery. 217 Note that this draft concentrates on the preservation of label state 218 for labels exchanged between a pair of adjacent LSRs when the TCP 219 connection between those LSRs is lost. The is a requirement for fault 220 tolerant operation of LSPs, but a full implementation of end-to-end 221 protection for LSPs requires that this is combined with other 222 techniques that are outside the scope of this draft. 224 In particular, this draft does not attempt to describe how to modify 225 the routing of an LSP or the resources allocated to a label or LSP, 226 which is covered by [5]. This draft also does not address how to 227 provide automatic layer 2/3 protection switching for a label or LSP, 228 which is a separate area for study. 230 3. Overview of LDP FT Enhancements 232 The LDP FT enhancements consist of the following main elements, which 233 are described in more detail in the sections that follow. 235 - The presence of an FT Session TLV on the LDP Initialization 236 message indicates that an LSR supports the LDP FT enhancements on 237 this session. 239 - An FT Reconnect Flag in the FT Session TLV indicates whether an 240 LSR has preserved FT label state across a failure of the TCP 241 connection. 243 - An FT Reconnection Timeout, exchanged on the LDP Initialization 244 message, that indicates the maximum time peer LSRs will preserve 245 FT label state after a failure of the TCP connection. 247 - An FT Protection TLV used to identify operations that affect LDP 248 labels. All LDP messages carrying the FT Protection TLV need to be 249 secured (e.g. to NVRAM) and ACKed to the sending LDP peer in order 250 that the state for FT labels can be correctly recovered after LDP 251 session reconnection. 253 3.1 Establishing an FT LDP Session 255 In order that the extensions to LDP [4] and CR-LDP [2] described in 256 this draft can be used successfully on an LDP session between a pair 257 of LDP peers, they MUST negotiate that the LDP FT enhancements 258 are to be used on the LDP session. 260 This is done on the LDP Initialization message exchange using a new 261 FT Session TLV. Presence of this TLV indicates that the 262 peer wants to support the LDP FT enhancements on this LDP session. 264 The LDP FT enhancements MUST be used on an LDP session if both 265 LDP peers include a FT Session TLV on the LDP Initialization message. 267 If either LDP Peer does not include the FT Session TLV on the LDP 268 Initialization message, the LDP FT enhancements MUST NOT be 269 used on the LDP session. 271 An LSR MAY present different FT/non-FT behavior on different TCP 272 connections, even if those connections are successive instantiations 273 of the LDP session between the same LDP peers. 275 3.1.1 Interoperation with Non-FT LSRs 277 The FT Session TLV on the LDP Initialization message carries the 278 U-bit. If an LSR does not support the LDP FT Enhancements, it will 279 ignore this TLV. Since such partners also do not include the FT 280 Session TLV, all LDP sessions to such LSRs will not use the LDP FT 281 enhancements. 283 The rest of this draft assumes that the LDP sessions under discussion 284 are between LSRs that do support the LDP FT Enhancements, except 285 where explicitly stated otherwise. 287 3.2 TCP Connection Failure 289 If the LDP FT enhancements are not in use on an LDP session, the 290 action of the LDP peers on failure of the TCP connection is as 291 specified in [2] and [4]. 293 All state information and resources associated with non-FT labels 294 MUST be released on the failure of the TCP connection, including 295 deprogramming the non-FT label from the switching hardware. This is 296 equivalent to the behavior specified in [4]. 298 If the LDP FT enhancements are in use on an LDP session, both LDP 299 peers SHOULD preserve state information and resources associated with 300 FT labels exchanged on the LDP session. Both LDP peers SHOULD use a 301 timer to release the preserved state information and resources 302 associated with FT-labels if the TCP connection is not restored 303 within a reasonable period. The behavior when this timer expires is 304 equivalent to the LDP session failure behavior described in [4]. 306 The FT Reconnection Timeout each LDP peer intends to apply to the LDP 307 session is carried in the FT Session TLV on the LDP Initialization 308 messages. It is RECOMMENDED that both LDP peers use the lower 309 timeout value from the LDP Initialization exchange when setting their 310 reconnection timer after a TCP connection failure. 312 3.3 Data Forwarding During TCP Connection Failure 314 An LSR that implements the LDP FT enhancements SHOULD preserve the 315 programming of the switching hardware across a failover. This 316 ensures that data forwarding is unaffected by the state of the TCP 317 connection between LSRs. 319 It is an integral part of FT failover processing in some hardware 320 configurations that some data packets might be lost. If data loss is 321 not acceptable to the applications using the MPLS network, the LDP FT 322 enhancements described in this draft SHOULD NOT be used. 324 3.4 FT LDP Session Reconnection 326 When the new TCP connection is established after FT failure, the LDP 327 peers MUST re-exchange LDP Initialization messages. 329 If an LDP peer includes the FT Session TLV in the LDP Initialization 330 message for the new insanitation of the LDP session, it MUST also 331 set the FT Reconnect Flag according to whether it has been able to 332 preserve label state. The FT Reconnect Flag is carried in the FT 333 Session TLV. 335 If an LDP peer has preserved all state information for previous 336 instantiations of the LDP session, then it SHOULD set the FT Reconnect 337 Flag to 1 in the FT Session TLV. Otherwise, it MUST set the FT 338 Reconnect Flag to 0. 340 If an LDP peer has preserved all state information for previous 341 instantiations of the LDP session, it MUST set the FT Reconnect Flag 342 to 1 in the FT Session TLV. 344 If either LDP peer sets the FT Reconnect Flag to 0, or omits the FT 345 Session TLV, both LDP peers MUST release any state information and 346 resources associated with the previous insanitation of the LDP 347 session between the same LDP peers, including FT label state and 348 Address ranges. This ensures that network resources are not 349 permanently lost by one LSR if its LDP peer is forced to undergo a 350 cold start. 352 If both LDP peers set the FT Reconnect Flag to 1, both LDP peers MUST 353 use the FT label operation procedures indicated in this draft to 354 complete any label operations on FT labels that were interrupted by 355 the LDP session failure. 357 3.5 Operations on FT Labels 359 Label operations on FT labels are made fault tolerant by providing 360 acknowledgement of all LDP messages that affect FT labels. 361 Acknowledgements are achieved by means of sequence numbers on these 362 LDP messages. 364 The message exchanges used to achieve acknowledgement of label 365 operations and the procedures used to complete interrupted label 366 operations are detailed in the section "FT Operations". 368 Using these acknowledgements and procedures, it is not necessary for 369 LDP peers to perform a complete re-synchronization of state for all 370 FT labels, either on re-connection of the LDP session between the LDP 371 peers or on a timed basis. 373 4. FT Operations 375 Once an FT LDP session has been established, using the procedures 376 described in section "Establishing an FT LDP Session", both LDP peers 377 MUST apply the procedures described in this section for FT LDP 378 message exchanges. 380 If the LDP session has been negotiated to not use the LDP FT 381 enhancements, these procedures MUST NOT be used. 383 4.1 FT LDP Messages 385 4.1.1 FT Label Messages 387 A label is identified as being an FT label if the initial Label 388 Request or Label Mapping message relating to that label carries the 389 FT Protection TLV. 391 If a label is an FT label, all LDP messages affecting that label MUST 392 carry the FT Protection TLV in order that the state of the label can 393 be recovered after a failure of the LDP session. 395 4.1.1.1 Scope of FT Labels 397 The scope of the FT/non-FT status of a label is limited to the 398 LDP message exchanges between a pair of LDP peers. 400 In Ordered Control, when the message is forwarded downstream or 401 upstream, the TLV may be present or absent according to the 402 requirements of the LSR sending the message. 404 4.1.2 FT Address Messages 406 If an LDP session uses the LDP FT enhancements, both LDP peers 407 MUST secure Address and Address Withdraw messages using FT Operation 408 ACKs, as described below. This avoids any ambiguity over whether 409 an Address range is still valid after the LDP session is reconnected. 411 If an LSR determines that an Address message that it sent on a 412 previous insanitation of a recovered LDP session is no longer valid, 413 it MUST explicitly issue an Address Withdraw for that range when the 414 session is reconnected. 416 If the FT Reconnect Flag is not set by both LDP peers on reconnection 417 of an LDP session (i.e. state has not been preserved), both LDP 418 peers MUST consider all Address ranges to have been withdrawn. The 419 LDP peers SHOULD issue new Address messages for all their valid 420 address ranges, as specified in [4]. 422 4.2 FT Operation ACKs 424 Handshaking of FT LDP messages is achieved by use of ACKs. 425 Correlation between the original message and the ACK is by means of 426 the FT Sequence Number contained in the FT Protection TLV, and passed 427 back in the FT ACK TLV. The FT ACK TLV may be carried on any LDP 428 message that is sent on the TCP connection between LDP peers. 430 A LDP peer maintains a separate FT sequence number for each LDP 431 session it participates in. The FT Sequence number is incremented by 432 one for each FT LDP message (i.e. containing the FT Protection TLV) 433 issued by this LSR on the FT LDP session with which the FT sequence 434 number is associated. 436 When an LDP Peer receives a message containing the FT Protection TLV, 437 it MUST take steps to secure this message (or the state information 438 derived from processing the message). Once the message is secured, it 439 MUST be ACKed. However, there is no requirement on the LSR to send 440 this ACK immediately. 442 ACKs may be accumulated. For example if a LSR received FT 443 LDP messages with sequence numbers 1, 2, 3, 4, it could send a single 444 ACK with sequence number 4 to ACK receipt and securing of all these 445 messages. 447 ACKs MUST NOT be sent out of sequence, as this is incompatible with 448 the use of accumulated ACKs to reduce the message flow between LDP 449 peers. 451 4.3 Preservation of FT State 453 If the LDP FT enhancements are in use on an LDP session, each LDP 454 peer SHOULD NOT release the state information and resources 455 associated with FT labels exchanged on that LDP session when the TCP 456 connection fails. This is contrary to [2] and [4], but allows label 457 operations on FT labels to be completed after re-connection of the 458 TCP connection. 460 Both LDP peers on a LDP session that is using the LDP FT enhancements 461 SHOULD preserve the state information and resources they hold for 462 that LDP session until one of the following occurs: 464 - An upstream LDP peer SHOULD release the resources (in 465 particular bandwidth) associated with an FT label when it 466 initiates a Label Release or Label Abort message for the label. 467 The upstream LDP peer MUST preserve state information for 468 the label, even if it releases the resources associated with the 469 label, as it may have to reissue the label operation if the 470 TCP connection is interrupted. 472 - An upstream LDP peer MUST release the state information 473 and resources associated with an FT label when it receives an 474 acknowledgement to a Label Release or Label Abort message that it 475 sent for the label, or when it sends a Label Release 476 message in response to a Label Withdraw message received from the 477 downstream LDP peer. 479 - A downstream LDP peer SHOULD NOT release the resources 480 associated with an FT label when it sends a Label Withdraw message 481 for the label as it has not yet received confirmation that the 482 upstream LDP peer has ceased to send data using the label. The 483 downstream LDP peer MUST NOT release the state information it 484 holds for the label as it may yet have to reissue the label 485 operation if the TCP connection is interrupted. 487 - A downstream LDP peer MUST release the resources and state 488 information associated with an FT label when it receives an 489 acknowledgement to a Label Withdraw message for the label. 491 - When the FT Reconnection Timeout expires, an LSR SHOULD release 492 all state information and resources from previous instantiations 493 of the (permanently) failed LDP session. 495 - When an LSR receives a Status TLV with the E-bit set in 496 the status code, which causes it to close the TCP connection, the 497 LSR MUST release all state information and resources associated 498 with the session. This behaviour is mandated because it is 499 impossible for the LSR to predict the precise state and future 500 behaviour of the partner LSR that issued the E-bit without 501 knowledge of the implementation of that partner LSR. 503 Note that the "Temporary Shutdown" status code does not carry the 504 E-bit, and MAY be used during maintenance or upgrade operations to 505 indicate that the LSR intends to preserve state across a closure 506 and re-establishment of the TCP session. 508 - If an LSR determines that it must release state for any FT 509 label during a failure of the TCP connection on which that label 510 was exchanged, it MUST release all state preserved for the same 511 LDP session. 513 The release of state information and resources associated with non-FT 514 labels is as described in [2] and [4]. 516 4.4 FT Procedure After TCP Failure 518 When an LSR discovers or is notified of a TCP connection failure it 519 SHOULD start an FT Reconnection Timer to allow a period for 520 re-connection of the TCP connection between the LDP peers. 522 Once the TCP connection between LDP peers has failed, the active LSR 523 SHOULD attempt to re-establish the TCP connection. The mechanisms, 524 timers and retry counts to re-establish the TCP connection are an 525 implementation choice. It is RECOMMENDED that any attempt to 526 re-establish the connection take account of the failover processing 527 necessary on the peer LSR, the nature of the network between the 528 LDP peers, and the FT Reconnection Timeout chosen on the previous 529 insanitation of the TCP connection (if any). 531 If the TCP connection cannot be re-established within the FT 532 Reconnection Timeout period, the LSR detecting this timeout SHOULD 533 release all state preserved for the failed LDP session. If the TCP 534 connection is subsequently re-established (for example after a 535 further Hello exchange to set up a new LDP session), the LSR MUST set 536 the FT Reconnect Flag to 0 if it released the preserved state 537 information on this timeout event. 539 If the TCP connection is successfully re-established within the FT 540 Reconnection Timeout, both peers MUST re-issue LDP operations that 541 were interrupted by the TCP connection failure. This procedure is 542 described in section "Procedure After TCP Re-connection". 544 The Hold Timer for an FT LDP Session SHOULD be ignored while the FT 545 Reconnection Timer is running. The hold timer SHOULD be restarted 546 when the TCP connection is re-established. 548 4.4.1 FT LDP Operations During TCP Failure 550 When the LDP FT enhancements are in use for an LDP session, it is 551 possible that an LSR may determine that it needs to send an LDP 552 message to a LDP peer but the TCP connection to that peer is 553 currently down. These label operations affect the state of FT labels 554 preserved for the failed TCP connection, so it is important that the 555 state changes are passed to the LDP peer when the TCP connection is 556 restored. 558 If an LSR determines that it needs to issue a new FT LDP operation to 559 an LDP peer to which the TCP connection has currently failed, it MUST 560 pend the operation (e.g. on a queue) and complete that operation 561 with the LDP peer when the TCP connection is restored, unless the 562 label operation is overridden by a subsequent additional operation 563 during the TCP connection failure (see section "Procedure After TCP 564 Re-connection") 566 In ordered operation, received FT LDP operations that cannot be 567 correctly forwarded because of a TCP connection failure MAY be 568 processed immediately (provided sufficient state is kept to forward 569 the label operation) or pended for processing when the onward TCP 570 connection is restored and the operation can be correctly forwarded 571 upstream or downstream. Operations on existing FT labels SHOULD NOT 572 be failed during TCP session failure. 574 It is RECOMMENDED that Label Request operations for new FT labels are 575 not pended awaiting the re-establishment of TCP connection that is 576 awaiting recovery at the time the LSR determines that it needs to 577 issue the Label Request message. Instead, such Label Request 578 operations SHOULD be failed and, if necessary, a notification message 579 containing the "No LDP Connection" status code sent upstream. 581 Label Requests for new non-FT labels MUST be rejected during TCP 582 connection failure, as specified in [2] and [4]. 584 4.5 FT Procedure After TCP Re-connection 586 The FT operation handshaking described above means that all state 587 changes for FT labels and Address messages are confirmed or 588 reproducible at each LSR. 590 If the TCP connection between LDP peers fails but is re-connected 591 within the FT Reconnection Timeout, both LDP peers on the connection 592 MUST complete any label operations for FT labels that were 593 interrupted by the failure and re-connection of the TCP connection. 594 Label operation are completed using the procedure described below. 596 4.5.1 Re-Issuing FT Messages 598 On restoration of the TCP connection between LDP peers, any FT 599 LDP messages that were lost because of the TCP connection 600 failure are re-issued. The LDP peer that receives a re-issued message 601 processes the message from scratch. 603 "Net-zero" combinations of messages need not be re-issued after 604 re-establishment of the TCP connection between LDP peers. This leads 605 to the following rules for re-issuing messages that are not ACKed by 606 the LDP peer on the LDP Initialization message exchange after 607 re-connection of the TCP session. 609 - A Label Request message MUST be re-issued unless a Label Abort 610 would be re-issued for the same Label Request or the Label Request 611 or if the requested label is no longer required. 613 - A Label Mapping message MUST be re-issued unless a Label Withdraw 614 message would be re-issued for the same FT label. 616 - All other messages on the LDP session that carried the FT 617 Protection TLV MUST be re-issued if an acknowledgement had not 618 previously been received. 620 Any FT label operations that were pended (see section "FT Label 621 Operations During TCP Failure") during the TCP connection failure 622 MUST also be issued on re-establishment of the LDP session, except 623 where they form part of a "net-zero" combination of messages 624 according to the above rules. 626 The determination of "net-zero" FT label operations according to the 627 above rules MAY be performed on pended messages prior to the 628 re-establishment of the TCP connection in order to optimize the use 629 of queue resources. Messages that were sent to the LDP peer before 630 the TCP connection failure, or pended messages that are paired with 631 them, MUST NOT be subject to such optimization until an FT ACK TLV is 632 received from the LDP peer. This ACK allows the LSR to identify 633 which messages were received by the LDP peer prior to the TCP 634 connection failure. 636 4.5.2 Interaction with CR-LDP LSP Modification 638 Re-issuing LDP messages for FT operation is orthogonal to the use of 639 duplicate messages marked with the Modify ActFlg, as specified in 640 [5]. Each time an LSR uses the modification procedure for an FT LSP 641 to issue a new Label Request message, the FT label operation 642 procedures MUST be separately applied to the new Label Request 643 message. 645 5. Changes to Existing Messages 647 5.1 LDP Initialization Message 649 The LDP FT enhancements add the following optional parameters to a 650 LDP Initialization message 652 Optional Parameter Length Value 654 FT Session TLV 4 See below 655 FT ACK TLV 4 See below 657 The encoding for these TLVs is found in Section "New Fields and 658 Values". 660 FT Session 661 If present, specifies the FT behavior of the LDP session. 663 FT ACK TLV 664 If present, specifies the last FT message that the sending LDP 665 peer was able to secure prior to the failure of the previous 666 insanitation of the LDP session. This TLV is only present if the 667 FT Reconnect flag is set in the FT Session TLV, in which case 668 this TLV MUST be present. 670 5.2 LDP Keepalive Messages 672 The LDP FT enhancements add the following optional parameter to a 673 LDP Keepalive message 675 Optional Parameter Length Value 677 FT ACK TLV 4 See below 679 The encoding for FT ACK TLV is found in Section "FT ACK TLV". 681 FT ACK TLV 682 If present, specifies the most recent FT message that the 683 sending LDP peer has been able to secure. 685 5.3 All Other LDP Session Messages 687 The LDP FT enhancements add the following optional parameters to all 688 other message types that flow on an LDP session after the LDP 689 Initialization message 691 Optional Parameter Length Value 693 FT Protection TLV 4 See below 694 FT ACK TLV 4 See below 696 The encoding for these TLVs is found in the section "New Fields and 697 Values". 699 FT Protection 700 If present, specifies FT Sequence Number for the LDP message. 702 FT ACK 703 If present, identifies the most recent FT LDP message 704 ACKed by the sending LDP peer. 706 6. New Fields and Values 708 6.1 Status Codes 710 The following new status codes are defined to indicate various error 711 conditions specific to the LDP FT enhancements. These status codes 712 are carried in the Status TLV of a Notification message. 714 The "E" column is the required setting of the Status Code E-bit; the 715 "Status Data" column is the value of the 30-bit Status Data field in 716 the Status Code TLV. 718 Note that the setting of the Status Code F-bit is at the discretion 719 of the LSR originating the Status TLV. However, it is RECOMMENDED 720 that the F-bit is not set on Notification messages containing 721 status codes 0x00000017 - 0x00000019 because the duplication of 722 messages SHOULD be restricted to being a per-hop behavior. 724 Status Code E Status Data 726 No LDP Session 0 0x00000016 727 Zero FT seqnum 1 0x00000017 728 Unexpected TLV / 1 0x00000018 729 Session Not FT 730 Unexpected TLV / 1 0x00000019 731 Label Not FT 732 Missing FT Protection TLV 1 0x0000001A 733 FT ACK sequence error 1 0x0000001B 734 Temporary Shutdown 0 0x0000001C 735 FT Seq Numbers Exhausted 1 0x0000001D 737 The Temporary Shutdown status code SHOULD be used in place of 738 the Shutdown status code (which carries the E-bit) if the LSR that is 739 shutting down wishes to inform its LDP peer that it expects to be 740 able to preserve FT label state and to return to service before the 741 FT Reconnection Timer expires. 743 6.2 FT Session TLV 745 LDP peers can negotiate whether the LDP session between them supports 746 FT extensions by using a new OPTIONAL parameter, the FT Session 747 TLV, on LDP Initialization Messages. 749 The FT Session TLV is encoded as follows. 751 0 1 2 3 752 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 1 753 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 754 |1|0| FT Session TLV (0x0503) | Length (= 4) | 755 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 756 | FT Flags | FT Reconnection Timeout | 757 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 759 FT Flags 760 FT Flags: A 16 bit field that indicates various attributes the 761 FT support on this LDP session. This fields is formatted as 762 follows: 764 0 1 765 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 766 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 767 |R| Reserved | 768 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 770 R: FT Reconnect Flag. 771 Set to 1 if the sending LSR has preserved state and 772 resources for all FT-labels since the previous LDP 773 session between the same LDP peers, and set to 0 774 otherwise. See the section "FT LDP Session 775 Reconnection" for details of how this flag is used. 777 If the FT Reconnect Flag is set, the sending LSR must 778 include an FT ACK TLV on the LDP Initialization message. 780 All other bits in this field are currently reserved and SHOULD 781 be set to zero on transmission and ignored on receipt. 783 FT Reconnection Timeout 784 The period of time the sending LSR will preserve state and 785 resources for FT labels exchanged on the previous insanitation of 786 an FT LDP session that has currently failed. The timeout is 787 encoded as a 16-bit unsigned integer number of seconds. 789 The value of 0 for this field is reserved and MUST NOT be used. 791 See the section "LDP Session Failure" for details of how this field 792 is used. 794 6.3 FT Protection TLV 796 LDP peers use the FT Protection TLV to indicate that an LDP message 797 contains an FT label operation. 799 The FT Protection TLV MUST NOT be used in messages flowing on an LDP 800 session that does not support the LDP FT enhancements. 802 The FT Protection TLV MAY be carried on an LDP message transported on 803 the LDP session after the initial exchange of LDP Initialization 804 messages. In particular, this TLV MAY optionally be present on the 805 following messages: 807 - Label Request Messages in downstream on-demand distribution mode 808 - Label Mapping messages in downstream unsolicited mode. 810 If a label is to be an FT label, then the Protection TLV MUST be 811 present: 812 - on the Label Request message in DoD mode 813 - on the Label Mapping message in DU mode 814 - on all subsequent messages concerning this label. 816 Here 'subsequent messages concerning this label' means any message 817 whose Label TLV specifies this label or whose Label Request Message ID 818 TLV specifies the initial Label Request message. 820 If a label is not to be an FT label, then the Protection TLV 821 MUST NOT be present on any of these messages. 823 The FT Protection TLV is encoded as follows. 825 0 1 2 3 826 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 1 827 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 828 |0|0| FT Protection (0x0203) | Length (= 4) | 829 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 830 | FT Sequence Number | 831 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 833 FT Sequence Number 834 The sequence number for this FT label operation. The 835 sequence number is encoded as a 32-bit unsigned integer. The 836 initial value for this field on a new LDP session is x00000001 and 837 is incremented by one for each FT LDP message issued by the sending 838 LSR on this LDP session. This field may wrap from xFFFFFFFF to 839 x00000000. 841 This field MUST be reset to x00000001 if either LDP peer does not 842 set the FT Reconnect Flag on re-establishment of the TCP 843 connection. 845 See the section "Use of FT Labels" for details of how this field 846 is used. 848 If an LSR receives an FT Protection TLV on a session that does not 849 support the FT LFP enhancements, it SHOULD send a Notification 850 message to its LDP peer containing the "Unexpected TLV, Session Not 851 FT" status code. 853 If an LSR receives an FT Protection TLV on an operation affecting a 854 label that it believes is a non-FT label, it SHOULD send a 855 Notification message to its LDP peer containing the "Unexpected TLV, 856 Label Not FT" status code. 858 If an LSR receives a message affecting a label that it believes is an 859 FT label, it SHOULD send a Notification message to its LDP peer 860 containing the "Missing FT Protection TLV" status code. 862 If an LSR receives a FT Protection TLV containing a zero FT 863 Sequence Number, it SHOULD send a Notification message to its LDP 864 peer containing the "Zero FT Seqnum" status code. 866 6.4 FT ACK TLV 868 LDP peers use the FT ACK TLV to acknowledge FT 869 label operations. 871 The FT ACK TLV MUST NOT be used in messages flowing on an 872 LDP session that does not support the LDP FT enhancements. 874 The FT ACK TLV MAY be present on any LDP message exchanged on an 875 LDP session after the initial LDP Initialization messages. It is 876 RECOMMENDED that the FT ACK TLV is included on all FT 877 Keepalive messages in order to ensure that the LDP peers do not 878 build up a large backlog of unacknowledged state information. 880 The FT ACK TLV is encoded as follows. 882 0 1 2 3 883 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 1 884 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 885 |0|0| FT ACK (0x0504) | Length (= 4) | 886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 887 | FT ACK Sequence Number | 888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 890 FT ACK Sequence Number 891 The sequence number for this most recent FT label message 892 that the sending LDP peer has received from the receiving LDP 893 peer and secured against failure of the LDP session. It is not 894 necessary for the sending peer to have fully processed the message 895 before ACKing it. For example, a LSR MAY ACK a Label Request 896 message as soon as it has securely recorded the message, without 897 waiting until it can send the Label Mapping message in response. 899 ACKs are cumulative. Receipt of a LDP message containing an FT 900 ACK TLV with an FT ACK Sequence Number of 12 is treated as the 901 acknowledgement of all messages from 1 to 12 inclusive (assuming 902 the LDP session started with a sequence number of 1). 904 This field MUST be set to 0 if the LSR sending the FT ACK TLV has 905 not received any FT label operations on this LDP session. This 906 would apply to LDP sessions to new LDP peers or after an LSR 907 determines that it must drop all state for a failed TCP connection. 909 See the section "Use of FT Labels" for details of how this field 910 is used. 912 If an LSR receives an FT ACK TLV on a session that does not 913 support the FT LFP enhancements, it SHOULD send a Notification 914 message to its LDP peer containing the "Unexpected TLV, Session Not 915 FT" status code. 917 If an LSR receives an FT ACK TLV that contains an FT ACK Sequence 918 Number that is less than the previously received FT ACK Sequence 919 Number (remembering to take account of wrapping), it SHOULD send a 920 Notification message to its LDP peer containing the "FT ACK 921 Sequence Error" status code. 923 7. Example Use 925 Consider two LDP peers, P1 and P2, implementing CR-LDP over a TCP 926 connection that connects them, and the message flow shown below. 928 The parameters shown on each message shown below are as follows: 930 message (label, senders FT sequence #, FT ACK #) 932 A "-" for FT ACK # means that the FT ACK TLV is not included on 933 that message. "n/a" means that the parameter in question is not 934 applicable to that type of message. 936 In the diagram below, time flows from top to bottom. The relative 937 position of each message shows when it is transmitted. See the notes 938 for a description of when each message is received, secured for FT or 939 processed. 941 notes P1 P2 942 ===== == == 943 (1) Label Request(L1,27,-) 944 ---------------------------> 945 Label Request(L2,28,-) 946 ---------------------------> 947 (2) Label Request(L3,93,27) 948 <--------------------------- 949 (3) Label Request(L1,123,-) 950 --------------------------> 951 Label Request(L2,124,-) 952 --------------------------> 953 (4) Label Mapping(L1,57,-) 954 <-------------------------- 955 Label Mapping(L1,94,28) 956 <--------------------------- 957 (5) Label Mapping(L2,58,-) 958 <-------------------------- 959 Label Mapping(L2,95,-) 960 <--------------------------- 961 (6) Address(n/a,29,-) 962 ---------------------------> 963 (7) Label Request(L4,30,-) 964 ---------------------------> 965 (8) Keepalive(n/a,na/,94) 966 ---------------------------> 967 (9) Label Abort(L3,96,-) 968 <--------------------------- 969 (10) ===== TCP Session lost ===== 971 (11) Label Withdraw(L1,59,-) 972 <-------------------------- 974 (12) === TCP Session restored === 976 LDP Init(n/a,n/a,95) 977 ---------------------------> 978 LDP Init(n/a,n/a,29) 979 <--------------------------- 980 (13) Label Request(L4,30,-) 981 ---------------------------> 982 (14) Label Mapping(L2,95,-) 983 <--------------------------- 984 Label Abort(L3,96,30) 985 <--------------------------- 986 (15) Label Withdraw(L1,97,-) 987 <--------------------------- 989 Notes: 990 ====== 992 (1) Assume that the LDP session has already been initialized. 993 P1 issues 2 new Label Requests using the next sequence numbers. 995 (2) P2 issues a third Label request to P1. At the time of sending 996 this request, P2 has secured the receipt of the label request 997 for L1 from P1, so it includes an ACK for that message. 999 (3) P2 Processes the Label Requests for L1 and L2 and forwards them 1000 downstream. Details of downstream processing are not shown in 1001 the diagram above. 1003 (4) P2 receives a Label Mapping from downstream for L1, which it 1004 forwards to P1. It includes an ACK to the Label Request for L2, 1005 as that message has now been secured and processed. 1007 (5) P2 receives the Label Mapping for L2, which it forwards to P1. 1008 This time it does not include an ACK as it has not received any 1009 further messages from P1. 1011 (6) Meanwhile, P1 sends a new Address Message to P2 . 1013 (7) P1 also sends a fourth Label Request to P2 1015 (8) P1 sends a Keepalive message to P2, on which it includes an ACK 1016 for the Label Mapping for L1, which is the latest message P1 has 1017 received and secured at the time the Keepalive is sent. 1019 (9) P2 issues a Label Abort for L3. 1021 (10) At this point, the TCP session goes down. 1023 (11) While the TCP session is down, P2 receives a Label Withdraw 1024 Message for L1, which it queues. 1026 (12) The TCP session is reconnected and P1 and P2 exchange LDP 1027 Initialization messages on the recovered session, which include 1028 ACKS for the last message each peer received and secured prior 1029 to the failure. 1031 (13) From the LDP Init exchange, P1 determines that it needs to 1032 re-issue the Label request for L4. 1034 (14) Similarly, P2 determines that it needs to re-issue the Label 1035 Mapping for L2 and the Label Abort. 1037 (15) P2 issues the queued Label Withdraw to P1. 1039 8. Security Considerations 1041 The LDP FT enhancements inherit similar security considerations to 1042 those discussed in [2] and [4]. 1044 The LDP FT enhancements allow the re-establishment of a TCP 1045 connection between LDP peers without a full re-exchange of the 1046 attributes of established labels, which renders LSRs that implement 1047 the extensions specified in this draft vulnerable to additional 1048 denial-of-service attacks as follows: 1050 - An intruder may impersonate an LDP peer in order to force a 1051 failure and reconnection of the TCP connection, but where the 1052 intruder does not set the FT Reconnect Flag on re-connection. 1053 This forces all FT labels to be released. 1055 - Similarly, an intruder could set the FT Reconnect Flag on 1056 re-establishment of the TCP session without preserving the state 1057 and resources for FT labels. 1059 - An intruder could intercept the traffic between LDP peers and 1060 override the setting of the FT Label Flag to be set to 0 for 1061 all labels. 1063 All of these attacks may be countered by use of an authentication 1064 scheme between LDP peers, such as the MD5-based scheme outlined in 1065 [4]. 1067 Alternative authentication schemes for LDP peers are outside the 1068 scope of this draft, but could be deployed to provide enhanced 1069 security to implementations of LDP, CR-LDP and the LDP FT 1070 enhancements. 1072 9. Implementation Notes 1074 9.1 FT Recovery Support on Non-FT LSRs 1076 In order to take full advantage of the FT capabilities of LSRs in the 1077 network, it may be that an LSR that does not itself contain the 1078 ability to recover from local hardware or software faults still needs 1079 to support the LDP FT enhancements described in this draft. 1081 Consider an LSR, P1, that is an LDP peer of a fully fault tolerant 1082 LSR, P2. If P2 experiences a fault in the hardware or software that 1083 serves an LDP session between P1 and P2, it may fail the TCP 1084 connection between the peers. When the connection is recovered, the 1085 LSPs/labels between P1 and P2 can only be recovered if both LSRs were 1086 applying the FT recovery procedures to the LDP session. 1088 9.2 ACK generation logic 1090 FT ACKs SHOULD be returned to the sending LSR as soon as is 1091 practicable in order to avoid building up a large quantity of 1092 unacknowledged state changes at the LSR. However, immediate 1093 one-for-one acknowledgements would waste bandwidth unnecessarily. 1095 A possible implementation strategy for sending ACKs to FT LDP 1096 messages is as follows: 1097 - A LSR secures received messages in order and tracks the sequence 1098 number of the most recently secured message, Sr. 1099 - On each LDP KeepAlive that the LSR sends, it attaches an FT ACK 1100 TLV listing Sr 1101 - Optionally, the LSR may attach an FT ACK TLV to any other LDP 1102 message sent between Keepalive messages if, for example, Sr has 1103 increased by more than a threshold value since the last ACK sent. 1105 This implementation combines the bandwidth benefits of accumulating 1106 ACKs while still providing timely ACKs. 1108 10. Acknowledgments 1110 The work in this draft is based on the LDP and CR-LDP ideas 1111 expressed by the authors of [2] and [4]. 1113 The ACK scheme used in this draft was inspired by the proposal by 1114 David Ward and John Scudder for restarting BGP sessions [9]. 1116 The authors would also like to acknowledge the careful review and 1117 comments of Nick Weeds, Piers Finlayson, Tim Harrison and Duncan 1118 Archer at Data Connection Ltd, and Peter Ashwood-Smith of Nortel. 1120 11. Intellectual Property Consideration 1122 The IETF has been notified of intellectual property rights claimed in 1123 regard to some or all of the specification contained in this 1124 document. For more information, consult the online list of claimed 1125 rights. 1127 12. Full Copyright Statement 1129 Copyright (c) The Internet Society (2000). All Rights Reserved. This 1130 document and translations of it may be copied and furnished to 1131 others, and derivative works that comment on or otherwise explain it 1132 or assist in its implementation may be prepared, copied, published 1133 and distributed, in whole or in part, without restriction of any 1134 kind, provided that the above copyright notice and this paragraph 1135 are included on all such copies and derivative works. However, this 1136 document itself may not be modified in any way, such as by removing 1137 the copyright notice or references to the Internet Society or other 1138 Internet organizations, except as needed for the purpose of 1139 developing Internet standards in which case the procedures for 1140 copyrights defined in the Internet Standards process must be 1141 followed, or as required to translate it into languages other than 1142 English. 1144 The limited permissions granted above are perpetual and will not be 1145 revoked by the Internet Society or its successors or assigns. 1147 This document and the information contained herein is provided on an 1148 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 1149 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 1150 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 1151 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 1152 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1154 13. IANA Considerations 1156 This draft requires the use of a number of new TLVs and status codes 1157 from the number spaces within the LDP protocol. This section 1158 explains the logic used by the authors to choose the most appropriate 1159 number space for each new entity, and is intended to assist in the 1160 determination of any final values assigned by IANA or the MPLS WG in 1161 the event that the MPLS WG chooses to advance this draft on the 1162 standards track. 1164 This section will be removed when the TLV and status code values have 1165 been agreed with IANA. 1167 13.1 FT Session TLV 1169 The FT Session TLV carries attributes that affect the entire LDP 1170 session between LDP peers. It is suggested that the type for this 1171 TLV should be chosen from the 0x05xx range for TLVs that is used in 1172 [4] by other TLVs carrying session-wide attributes. At the time of 1173 this writing, the next available number in this range is 0x0503. 1175 13.2 FT Protection TLV 1177 The FT Protection TLV carries attributes that affect a single label 1178 exchanged between LDP peers. It is suggested that the type for this 1179 TLV should be chosen from the 0x02xx range for TLVs that is used in 1180 [4] by other TLVs carrying label attributes. At the time of this 1181 writing, the next available number in this range is 0x0203. 1183 Consideration was given to using the message number field instead of 1184 a new FT Sequence Number field. However, the authors felt this 1185 placed unacceptable implementation constraints on the use of message 1186 number (e.g. it could no longer be used to reference a control 1187 block). 1189 13.3 FT ACK TLV 1191 The FT Protection TLV may ACK many label operations at once 1192 if cumulative ACKS are used. It is suggested that the type for this 1193 TLV should be chosen from the 0x05xx range for TLVs that is used in 1194 [4] by other TLVs carrying session-wide attributes. At the time of 1195 this writing, the next available number in this range is 0x0504. 1197 Consideration was given to carrying the FT ACK Number in the FT 1198 Protection TLV, but the authors felt this would be inappropriate as 1199 many implementations may wish to carry the ACKs on Keepalive 1200 messages. 1202 13.4 Status Codes 1204 The authors' current understanding is that MPLS status codes are not 1205 sub-divided into specific ranges for different types of error. 1206 Hence, the numeric status code values suggested in this draft are 1207 simply the next available values at the time of writing and may be 1208 substituted for other numeric values. 1210 See section "Status Codes" for details of the status codes defined in 1211 this draft. 1213 14. Authors' Addresses 1215 Adrian Farrel Paul Brittain (editor) 1216 Data Connection Ltd. Data Connection Ltd. 1217 Windsor House Windsor House 1218 Pepper Street Pepper Street 1219 Chester Chester 1220 Cheshire Cheshire 1221 CH1 1DF CH1 1DF 1222 UK UK 1223 Phone: +44-(0)-1244-313440 Phone: +44-(0)-1244-313440 1224 Fax: +44-(0)-1244-312422 Fax: +44-(0)-1244-312422 1225 Email: af@datcon.co.uk Email: pjb@datcon.co.uk 1227 Philip Matthews Eric Gray 1228 Nortel Networks Corp. Zaffire, Inc. 1229 P.O. Box 3511 Station C, 2630 Orchard Parkway, 1230 Ottawa, ON K1Y 4H7 San Jose, CA - 95134-2020 1231 Canada Phone: (408) 894-7362 1232 Phone: +1 613-768-3262 egray@zaffire.com 1233 philipma@nortelnetworks.com 1235 15. References 1237 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 1238 9, RFC 2026, October 1996. 1240 2 Jamoussi, B., et. al., Constraint-Based LSP Setup using LDP, 1241 draft-ietf-mpls-cr-ldp-03.txt, September 1999,(work in progress). 1243 3 Bradner, S., "Key words for use in RFCs to Indicate Requirement 1244 Levels", BCP 14, RFC 2119, March 1997. 1246 4 Andersson, L., et. al., LDP Specification, draft-ietf-mpls-ldp- 1247 06.txt, October 1999 (work in progress). 1249 5 Ash, G., et al., LSP Modification Using CR-LDP, draft-ietf-mpls- 1250 crlsp-modify-01.txt, February 1000 (work in progress). 1252 6 Braden, R., et al., Resource ReSerVation Protocol (RSVP) -- 1253 Version 1, Functional Specification, RFC 2205, September 1997. 1255 7 Berger, L., et al., RSVP Refresh Reduction Extensions, draft- 1256 ietf-rsvp-refresh-reduct-04.txt, April 2000 (work in progress). 1258 8 Swallow, G., et al,. Extensions to RSVP for LSP Tunnels, draft- 1259 ietf-mpls-rsvp-lsp-tunnel-04.txt, September 1999 (work in 1260 progress). 1262 9 Ward, D, et al., BGP Notification Cease: I'll Be Back, 1263 draft-ward-bgp4-ibb-00.txt, June 1999 (work in progress) 1265 10 Stewart, R, et al., Simple Control Transmission Protocol, 1266 draft-ietf-sigtran-sctp-07.txt, March 2000 (work in progress)