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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references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4379 (Obsoleted by RFC 8029) == Outdated reference: A later version (-03) exists of draft-ietf-mpls-opportunistic-encrypt-00 Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force N. Akiya 3 Internet-Draft Big Switch Networks 4 Updates: 7110 (if approved) G. Swallow 5 Intended status: Standards Track C. Pignataro 6 Expires: April 10, 2016 Cisco Systems 7 L. Andersson 8 M. Chen 9 Huawei 10 October 8, 2015 12 Label Switched Path (LSP) Ping/Traceroute Reply Mode Simplification 13 draft-ietf-mpls-lsp-ping-reply-mode-simple-05 15 Abstract 17 The Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) 18 Ping and Traceroute use the Reply Mode field to signal the method to 19 be used in the MPLS echo reply. This document updates the procedures 20 for the "Reply via Specified Path" Reply Mode, the value of this 21 Reply Mode is 5. The update creates a simple way to indicate that 22 the Reverse LSP should be used as return path. This document also 23 adds an optional TLV which can carry ordered list of Reply Mode 24 values. 26 This document updates RFC7110. 28 Requirements Language 30 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 31 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 32 document are to be interpreted as described in RFC 2119 [RFC2119]. 34 Status of This Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at http://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on April 10, 2016. 50 Copyright Notice 52 Copyright (c) 2015 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. Problem Statements . . . . . . . . . . . . . . . . . . . . . 3 69 3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 5 70 3.1. Reply via Specified Path Update . . . . . . . . . . . . . 5 71 3.2. Reply Mode Order TLV . . . . . . . . . . . . . . . . . . 6 72 4. Relations to Other LSP Ping/Trace Features . . . . . . . . . 8 73 4.1. Backwards Compatibility with Reply via Specified Path 74 Reply Mode . . . . . . . . . . . . . . . . . . . . . . . 8 75 4.2. Reply Path TLV . . . . . . . . . . . . . . . . . . . . . 8 76 4.2.1. Example 1: Reply Mode Order TLV Usage with Reply Path 77 TLV . . . . . . . . . . . . . . . . . . . . . . . . . 9 78 4.2.2. Example 2: Reply Mode Order TLV Usage with Reply Path 79 TLV . . . . . . . . . . . . . . . . . . . . . . . . . 10 80 4.3. Proxy LSP Ping . . . . . . . . . . . . . . . . . . . . . 10 81 4.3.1. Proxy LSR Sending an MPLS Echo Request . . . . . . . 10 82 4.3.2. Proxy LSR Sending an MPLS Proxy Ping Reply . . . . . 11 83 5. Security Considerations . . . . . . . . . . . . . . . . . . . 11 84 6. Manageability Considerations . . . . . . . . . . . . . . . . 11 85 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 86 7.1. New Reply Mode Order TLV . . . . . . . . . . . . . . . . 12 87 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 88 9. Contributing Authors . . . . . . . . . . . . . . . . . . . . 12 89 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 90 10.1. Normative References . . . . . . . . . . . . . . . . . . 13 91 10.2. Informative References . . . . . . . . . . . . . . . . . 13 92 Appendix A. Reply Mode Order TLV Beneficial Scenarios . . . . . 13 93 A.1. Incorrect Forwarding Scenario . . . . . . . . . . . . . . 14 94 A.2. Non-Co-Routed Bidirectional LSP Scenario . . . . . . . . 14 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 97 1. Introduction 99 The Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) 100 Ping, described in [RFC4379], allows an initiator LSR to encode 101 instructions (Reply Mode) on how a responder LSR should send the 102 response back to the initiator LSR. [RFC7110] also allows the 103 initiator LSR to encode a TLV (Reply Path TLV) which can instruct the 104 responder LSR to use a specific LSP to send the response back to the 105 initiator LSR. Both approaches are powerful as they provide the 106 ability for the initiator LSR to control the return path. 108 However, it is becoming increasingly difficult for an initiator LSR 109 to select a valid return path to encode in the MPLS LSP echo request 110 packets. If the initiator LSR does not select a valid return path, 111 the MPLS LSP echo reply will not get back to the initiator LSR. This 112 results in a false failure of MPLS LSP Ping and Traceroute operation. 113 In an effort to minimize such false failures, different 114 implementations have chosen different default return path encoding 115 for different LSP types and LSP operations. The problem with 116 implementations having different default return path encoding is that 117 the MPLS echo reply will not work in many cases, and the default 118 value may not be the preferred choice by the operators. 120 This document describes: 122 o In Section 2, further description of the problems; 124 o In Section 3, a solution to minimize false failures while 125 accommodating operator preferences; 127 o In Section 4, relationships to other LSP Ping/Traceroute features; 129 o In Appendix A, examples of scenarios where the mechanism described 130 in this document provides benefits. 132 This document updates [RFC7110] by allowing the usage of the "Reply 133 via Specified Path" (value=5) Reply Mode without including the Reply 134 Path TLV. The update creates a simple way to indicate that the 135 Reverse LSP should be used as return path. 137 2. Problem Statements 139 It is becoming increasingly difficult for implementations to 140 automatically supply a workable return path encoding for all MPLS LSP 141 Ping and Traceroute operations across all LSP types. There are 142 several factors which are contributing to this complication. 144 o Some LSPs have a control-channel, and some do not. Some LSPs have 145 a reverse LSP, and some do not. Some LSPs have IP reachability in 146 the reverse direction, and some do not. 148 o LSRs on some LSPs can have different available return path(s). 149 Available return path(s) can depend on whether the responder LSR 150 is a transit LSR or an egress LSR. In case of a bi-directional 151 LSP, available return path(s) on transit LSRs can also depend on 152 whether the LSP is completely co-routed, partially co-routed or 153 associated (i.e., the LSPs in the two directions are not co- 154 routed). 156 o MPLS echo request packets may incorrectly terminate on an 157 unintended target, which can have different available return 158 path(s) than the intended target. 160 o The MPLS LSP Ping operation is expected to terminate on an egress 161 LSR. However, the MPLS LSP Ping operation with specific TTL 162 values and MPLS LSP Traceroute operation can terminate on both 163 transit LSR(s) and the egress LSR. 165 Except for the case where the responder LSR does not have an IP route 166 back to the initiator LSR, it is possible to use the "Reply via an 167 IPv4/IPv6 UDP packet" (value=2) Reply Mode value in all cases. 168 However, some operators are preferring control-channel and reverse 169 LSP as default return path if they are available, which is not always 170 the case. 172 When specific return path encoding is supplied by users or 173 applications, then there are no issues in choosing the return path 174 encoding. When specific return path encoding is not supplied by 175 users or applications, then implementations use extra logic to 176 compute, and sometimes guess, the default return path encodings. If 177 a responder LSR receives an MPLS echo request containing return path 178 instructions which cannot be accommodated due to unavailability, then 179 the responder LSR often drops such packets. This failure mode 180 results in the initiator LSR not receiving the intended MPLS LSP echo 181 reply packets. The scenario described here is a potentially 182 acceptable result in some failure cases, like a broken LSP, where the 183 MPLS echo request terminated on an unintended target. However, if 184 the initiator LSR does not receive an MPLS echo replay, even after 185 the responder LSR receives the MPLS echo request and is able to 186 verify the request, information is sent back to the user(s) which is 187 considered a false failure. 189 Many operators prefer particular return path(s) over others return 190 path(s) for specific LSP types. To accommodate operator preferred 191 paths, implementations may default to operator preferred return paths 192 for particular operations, or allow a default return path to be 193 configured. It would not be considered beneficial to use a preferred 194 return path for an intended target LSR if there is previous knowledge 195 at the initiator LSR that the return path is not available. Using a 196 unavailable preferred return path would undesirably result in the 197 initiator LSR not receiving the MPLS echo return packets. It would 198 be considered beneficial, for given operations, if the sender of the 199 MPLS echo request would be able to determined return path 200 availability before the operation is initiated. 202 This document updates the procedures for "Reply via Specified Path" 203 Reply Mode to easily indicate the reverse LSP, and adds one optional 204 TLV to describe an ordered list of Reply Modes. Based on operational 205 needs, the TLV can describe multiple Reply Mode values in a preferred 206 order to allow the responder LSR to use the first available Reply 207 Mode from the list. This eliminates the need for the initiator LSR 208 to compute, or sometimes guess, the default return path encoding. 209 This new mode of operation would resulted in a simplification to 210 implementations across the various vendors and improve both usability 211 and operational needs. 213 3. Solution 215 This document updates the procedures for "Reply via Specified Path" 216 Reply Mode to easily indicate the reverse LSP. This document also 217 adds an optional TLV which can carry an ordered list of Reply Modes. 219 3.1. Reply via Specified Path Update 221 Some LSP types are capable of having a related LSP in reverse 222 direction, through signaling or other association mechanisms. 223 Examples of such LSP types are bidirectional Resource ReserVation 224 Protocol-Traffic Engineering (RSVP-TE) LSPs [RFC3473] and MPLS 225 Transport Profile (MPLS-TP) LSPs ([RFC5960]). This document uses the 226 term "Reverse LSP" to refer to the LSP in the reverse direction of 227 such LSP types. Note that this document restricts the scope of 228 "Reverse LSP" applicability to those reverse LSPs which are capable 229 and allowed to carry the IP encapsulated MPLS echo reply. 231 [RFC7110] has defined the Reply Mode "Reply via Specified Path" which 232 allows the initiator LSR to instruct the responder LSR to send the 233 MPLS echo reply message on the reverse LSP. However, the instruction 234 also requires the initiator LSR to include the "Reply Path TLV" with 235 the B bit (Bidirectional bit) set in the Flags field. Additionally, 236 [RFC7110] defines that if the "Reply via Specified Path" Reply Mode 237 is used the "Reply Path TLV" MUST present. 239 This document updates the procedures for "Reply via Specified Path" 240 Reply Mode as follows: 242 o The "Reply via Specified Path" MAY be used without including a 243 "Reply Path TLV". 245 o The usage of the "Reply via Specified Path" without inclusion of a 246 "Reply Path TLV" implies the reverse LSP. In other words, the 247 usage of the "Reply via Specified Path" without inclusion of a 248 "Reply Path TLV" has the same semantics as the usage of the "Reply 249 via Specified Path" with inclusion of a "Reply Path TLV" with the 250 B bit set in the Flags field. 252 Specific to section 5.1 of [RFC7110], this document updates the first 253 sentence as follows: 255 o When sending an echo request, in addition to the rules and 256 procedures defined in Section 4.3 of [RFC4379], the Reply Mode of 257 the echo request MUST be set to "Reply via Specified Path", and a 258 Reply Path TLV SHOULD be carried in the echo request message 259 correspondingly; if the Reply Path TLV is not carried, then it 260 indicates the reverse LSP as the reply path. 262 Note that the reverse LSP is in relation to the last FEC specified in 263 the Target FEC Stack TLV. 265 3.2. Reply Mode Order TLV 267 This document also introduces a new optional TLV to describe a list 268 of Reply Mode values. The new TLV will contain one or more Reply 269 Mode value(s) in preferred order. The first Reply Mode value is the 270 most preferred and the last Reply Mode value is the least preferred. 271 Following rules apply when using Reply Mode Order TLV. 273 1. The Reply Mode Order TLV MUST NOT be included in any MPLS echo 274 reply. If the initiator LSR receives an MPLS echo reply with the 275 Reply Mode Order TLV, the initiator LSR MUST ignore the whole 276 Reply Mode Order TLV and MUST only use the value from the Reply 277 Mode field of the received MPLS echo reply. It may be beneficial 278 for implementations to provide counters and/or loggings, with 279 appropriate log dampening, to record this error case. 281 2. The Reply Mode Order TLV MAY be included in MPLS echo request. 283 3. The Reply Mode field of an MPLS echo request MUST be set to a 284 valid value even when supplying the Reply Mode Order TLV. The 285 initiator LSR SHOULD set the Reply Mode field of an MPLS echo 286 request to a value that corresponds to a return path which most 287 likely to be available, in case the responder LSR does not 288 understand the Reply Mode Order TLV. 290 4. If a responder LSR understands the Reply Mode Order TLV but the 291 TLV is not valid (due to conditions described in the items 6, 7, 292 8 and 9 immediately below), then the responder LSR MUST ignore 293 the whole Reply Mode Order TLV and MUST only use the value from 294 the Reply Mode field of the received MPLS echo request. It may 295 be beneficial for implementations to provide counters and/or 296 loggings, with appropriate log dampening, to record this error 297 case. 299 5. If a responder LSR understands the Reply Mode Order TLV and the 300 TLV is valid, then the responder LSR MUST consider the Reply Mode 301 values described in the TLV and MUST NOT use the value described 302 in the Reply Mode field of the received MPLS echo request. In 303 other words, a valid Reply Mode Order TLV overrides the value 304 specified in the Reply Mode field of the received MPLS echo 305 request. 307 6. Reply Mode Order TLV MUST contain at least one Reply Mode value. 309 7. A Reply Mode value, except for Reply Mode value 5 (Reply via 310 Specified Path), MUST NOT be repeated (i.e., MUST NOT appear 311 multiple times) in the Reply Mode Order TLV. 313 8. The Reply Mode value 5 (Reply via Specified Path) MAY be included 314 more than once in the Reply Mode Order TLV. However, in such 315 case a Reply Path TLV MUST be included for all instances of the 316 Reply Mode value 5 included in the Reply Mode Order TLV. In 317 other words, 3 instances of the Reply Mode value 5 in the Reply 318 Mode Order TLV will require 3 instances of the Reply Path TLVs. 320 9. The Reply Mode value 1 (Do not reply) MUST NOT be used in the 321 Reply Mode Order TLV. 323 The responder LSR SHOULD select the first available return path in 324 this TLV. The Reply Mode value corresponding to the selected return 325 path MUST be set in Reply Mode field of the MPLS echo reply to 326 communicate back to the initiator LSR which return path was chosen. 328 The format of the TLV is as follows: 330 0 1 2 3 331 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 1 332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 | Reply Mode Order TLV Type | Length | 334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 ~ Reply Mode 1 | Reply Mode 2 | Reply Mode 3 | Reply Mode 4 ~ 336 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 337 Figure 1 Reply Mode Order TLV 339 This is a variable length optional TLV. The Reply Mode Order TLV 340 Type is TBD1. 342 The Length field is 2 octets in length. It defines the length in 343 octets of the list of Reply Mode values. 345 Each Reply Mode field is 1 octet, and there is no padding. 347 4. Relations to Other LSP Ping/Trace Features 349 4.1. Backwards Compatibility with Reply via Specified Path Reply Mode 351 [RFC7110] introduces the "Reply via Specified Path" (value=5) Reply 352 Mode. The RFC also defines that if this Reply Mode is used, the 353 "Reply Path TLV" MUST be included. This document relaxes the 354 semantics and defines that this Reply Mode MAY be used without the 355 "Reply Path TLV". This MAY be done to indicate that the reverse LSP 356 SHALL be used as he return path. 358 If the initiator LSR, which sent an MPLS echo request message with 359 the "Reply via Specified Path" Reply Mode but without including the 360 "Reply Path TLV", receives back an MPLS echo reply message with the 361 return code being "Malformed echo request received", then the 362 initiator LSR SHOULD assume that the responder LSR does not support 363 the mechanism defined in this document. 365 4.2. Reply Path TLV 367 A "Reply Path TLV" [RFC7110] is defined to identify a single return 368 path. When the initiator LSR wants to use the Reply Mode Order TLV 369 to describe multiple return paths, then the initiator SHOULD include 370 multiple "Reply via Specified Path" (value=5) Reply Mode values and 371 multiple corresponding "Reply Path TLV" objects (one "Reply Path TLV" 372 corresponding to a "Reply via Specified Path" Reply Mode, and one 373 "Reply Path TLV" identifies a return path). 375 As described in Section 3.1, it's valid to use the "Reply via 376 Specified Path" Reply Mode without inclusion a "Reply Path TLV". For 377 the Reply Mode Order TLV, it's also valid to include a "Reply via 378 Specified Path" Reply Mode value without a corresponding "Reply Path 379 TLV", this implies that the reverse LSP is the preferred return path. 380 When multiple consecutive "Reply via Specified Path" Reply Mode 381 values are included but less corresponding "Reply Path TLV" objects 382 exist, the responder LSR SHOULD think that the former "Reply via 383 Specified Path" Reply Mode values have corresponding "Reply Path 384 TLV", the latter "Reply via Specified Path" Reply Mode values have no 385 corresponding "Reply Path TLV". For example, if the Reply Mode Order 386 TLV carrying Reply Modes {5, 5, 5} and only two Reply Path TLVs 387 carrying FEC X and FEC Y respectively. The reply path order is as 388 follows: 390 1. Reply via Specified Path (FEC X) 392 2. Reply via Specified Path (FEC Y) 394 3. Reply via Specified Path (Reverse LSP) 396 4.2.1. Example 1: Reply Mode Order TLV Usage with Reply Path TLV 398 If the initiator LSR was interested in encoding following return 399 paths: 401 1. Reply via application level control channel 403 2. FEC X 405 3. FEC Y 407 4. Reply via an IPv4/IPv6 UDP packet 409 Then the MPLS echo request message is to carry: 411 o The Reply Mode Order TLV carrying Reply Modes {4, 5, 5, 2} 413 o One Reply Path TLV carrying FEC X 415 o One Reply Path TLV carrying FEC Y 417 Described encoding of the Reply Mode Order TLV and the Reply Path TLV 418 in the MPLS echo request message will result in the responder LSR to 419 prefer "Reply via application level control channel (4)", followed by 420 FEC X, FEC Y and then "Reply via an IPv4/IPv6 UDP packet (2)". 422 4.2.2. Example 2: Reply Mode Order TLV Usage with Reply Path TLV 424 If the initiator LSR was interested in encoding following return 425 paths: 427 1. Reverse LSP 429 2. Reply via an IPv4/IPv6 UDP packet 431 3. FEC X 433 4. FEC Y 435 Then the MPLS echo request message is to carry: 437 o The Reply Mode Order TLV carrying Reply Modes {5, 2, 5, 5} 439 o One Reply Path TLV with the B bit set. 441 o One Reply Path TLV carrying FEC X 443 o One Reply Path TLV carrying FEC Y 445 Described encoding of the Reply Mode Order TLV and the Reply Path TLV 446 in the MPLS echo request message will result in the responder LSR to 447 prefer the reverse LSP, followed by "Reply via an IPv4/IPv6 UDP 448 packet (2)", FEC X and then FEC Y. 450 4.3. Proxy LSP Ping 452 The mechanism defined in this document will work with Proxy LSP Ping 453 defined by [RFC7555]. The MPLS proxy ping request message can carry 454 a Reply Mode value in the header and one or more Reply Mode values in 455 the Reply Mode Order TLV. It is RECOMMENDED that the Reply Mode 2 456 (Reply via an IPv4/IPv6 UDP packet) be used in the Reply Mode field 457 of the MPLS proxy ping request message. 459 4.3.1. Proxy LSR Sending an MPLS Echo Request 461 If the proxy LSR is sending an MPLS echo request, then the proxy LSR 462 MUST copy the following elements from the MPLS proxy ping request 463 message to the MPLS echo request message. 465 o The Reply Mode field. 467 o The Reply Mode Order TLV. 469 o The Reply Path TLV(s). If there are more than one Reply Path 470 TLVs, then order of them MUST be preserved when copying. 472 4.3.2. Proxy LSR Sending an MPLS Proxy Ping Reply 474 If the proxy LSR is sending an MPLS proxy ping reply, then it is 475 RECOMMENDED that the Reply Mode Order TLV is ignored and the Reply 476 Mode field in the MPLS proxy ping request message is used. 478 5. Security Considerations 480 Those security considerations specified in [RFC4379] and [RFC7110] 481 apply for this document. 483 In addition, this document introduces the Reply Mode Order TLV. It 484 provides a new way for an unauthorized source to gather more network 485 information, especially the potential return path(s) information of 486 an LSP. To protect against unauthorized sources using MPLS echo 487 request messages with the Reply Mode Order TLV to obtain network 488 information, similar to [RFC4379], it is RECOMMENDED that 489 implementations provide a means of checking the source addresses of 490 MPLS echo request messages against an access list before accepting 491 the message. 493 Another potential security issue is that the MPLS echo request and 494 reply messages are not encrypted, the content of the MPLS echo 495 request and reply messages may be potentially exposed. Although the 496 exposure is within the MPLS domain, if such exposure is a concern, 497 some encryption mechanisms [I-D.ietf-mpls-opportunistic-encrypt] may 498 be employed. 500 6. Manageability Considerations 502 Section 2 described the problems which increases the complexity with 503 respect to operations and implementations. In order to simplify 504 operations and to allow for the LSP Ping/Traceroute to function 505 efficiently whilst preserving the code simplicity, it is RECOMMENDED 506 that implementations allow devices to have configuration options to 507 set operator preferred Reply Modes. For example: 509 o For those operators who are more interested in MPLS echo reply 510 packets reaching back to the initiator LSR: 512 1. Reply via an IPv4/IPv6 UDP packet (2) 514 2. Reply via application level control channel (4) 516 3. Reply via Specified Path (5) 518 o For those operators who are more interested in MPLS echo reply 519 packets testing the paths related to the forward LSP: 521 1. Reply via Specified Path (5) 523 2. Reply via application level control channel (4) 525 3. Reply via an IPv4/IPv6 UDP packet (2) 527 7. IANA Considerations 529 7.1. New Reply Mode Order TLV 531 IANA is requested to assign a new TLV type value from the "TLVs" sub- 532 registry within the "Multiprotocol Label Switching Architecture 533 (MPLS)" registry, for the "Reply Mode Order TLV". 535 The new TLV Type value should be assigned from the range 536 (32768-49161) specified in [RFC4379] section 3 that allows the TLV 537 type to be silently dropped if not recognized. 539 Type Meaning Reference 540 ---- ------- --------- 541 TBD1 Reply Mode Order TLV this document 543 8. Acknowledgements 545 Authors would like to thank Santiago Alvarez and Faisal Iqbal for 546 discussions which motivated creation of this document. Authors would 547 also like to thank Sam Aldrin, Curtis Villamizar, Ross Callon, 548 Jeffrey Zhang, Jeremy Whittaker, Mustapha Alissaoui, Qin Wu, Jie Dong 549 and Adrian Farrel for providing valuable comments to influence the 550 contents of the draft. Authors would also like to thank Dan Frost, 551 Tom Taylor, Victor Kuarsingh and Deborah Brungard for reviewing the 552 document and providing useful comments. 554 9. Contributing Authors 556 Shaleen Saxena 557 Brocade 558 Email: ssaxena@brocade.com 560 10. References 561 10.1. Normative References 563 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 564 Requirement Levels", BCP 14, RFC 2119, 565 DOI 10.17487/RFC2119, March 1997, 566 . 568 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 569 Label Switched (MPLS) Data Plane Failures", RFC 4379, 570 DOI 10.17487/RFC4379, February 2006, 571 . 573 [RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord, 574 "Return Path Specified Label Switched Path (LSP) Ping", 575 RFC 7110, DOI 10.17487/RFC7110, January 2014, 576 . 578 10.2. Informative References 580 [I-D.ietf-mpls-opportunistic-encrypt] 581 Farrel, A. and S. Farrell, "Opportunistic Security in MPLS 582 Networks", draft-ietf-mpls-opportunistic-encrypt-00 (work 583 in progress), July 2015. 585 [RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label 586 Switching (GMPLS) Signaling Resource ReserVation Protocol- 587 Traffic Engineering (RSVP-TE) Extensions", RFC 3473, 588 DOI 10.17487/RFC3473, January 2003, 589 . 591 [RFC5960] Frost, D., Ed., Bryant, S., Ed., and M. Bocci, Ed., "MPLS 592 Transport Profile Data Plane Architecture", RFC 5960, 593 DOI 10.17487/RFC5960, August 2010, 594 . 596 [RFC7555] Swallow, G., Lim, V., and S. Aldrin, "Proxy MPLS Echo 597 Request", RFC 7555, DOI 10.17487/RFC7555, June 2015, 598 . 600 Appendix A. Reply Mode Order TLV Beneficial Scenarios 602 This section lists examples of how the Reply Mode Order TLV can 603 benefit. 605 A.1. Incorrect Forwarding Scenario 607 As shown in Figure 2, a network has an LSP with the forwarding path: 608 A-B-C-D-E. The LSP has a control channel. 610 A------B------C------D------E 611 | 612 | 613 F 615 Forward Paths: A-B-C-D-E 617 Figure 2: Incorrect Forwarding 619 If D is incorrectly label switching to F (instead of E). In this 620 scenario, LSP Traceroute with "Reply via application level control 621 channel (4)" will result in following result. 623 Success (Reply from B) 624 Success (Reply from C) 625 Success (Reply from D) 626 Timeout... 627 Complete 629 This is because F does not have a control channel to send the MPLS 630 echo reply message. With the extension described in this document, 631 same procedures can be performed with the Reply Mode Order TLV 632 carrying {4, 2}. When LSP Traceroute is issued, then following output 633 may be displayed without any unnecessary timeout. 635 Success (Reply from B, Reply Mode: 4) 636 Success (Reply from C, Reply Mode: 4) 637 Success (Reply from D, Reply Mode: 4) 638 FEC Mismatch (Reply from F, Reply Mode: 2) 639 Complete 641 The result provides more diagnostic information to the initiator LSR, 642 and without any delay (i.e. timeout from one or more downstream 643 LSRs). 645 A.2. Non-Co-Routed Bidirectional LSP Scenario 647 As shown in Figure 3, a network has a bidirectional LSP where the 648 forward LSP and the reverse LSP are not fully co-routed. 650 +----C------D----+ 651 / \ 652 A------B G------H 653 \ / 654 +----E------F----+ 656 Forward Paths: A-B-C-D-G-H (upper path) 657 Reverse Paths: H-G-F-E-B-A (lower path) 659 Figure 3: Non-Co-Routed Bidirectional LSP 661 Some operators may prefer and configure the system to default the 662 Reply Mode to indicate the reverse LSP when MPLS echo request 663 messages are sent on bidirectional LSPs. Without extensions 664 described in this document, following behaviors will be seen: 666 o When LSP Ping is issued from A, the reply will come back on the 667 reverse LSP from H. 669 o When LSP Traceroute is issued from A, the replies will come back 670 on the reverse LSP from B, G and H, but will encounter a timeout 671 from C and D as there are no reverse LSP on those nodes. 673 o When LSP Ping with specific TTL value is issued from A, whether a 674 timeout will be encountered depends on the value of the TTL used 675 (i.e. whether or not the MPLS echo request terminates on a node 676 that has reverse LSP). 678 One can argue that the initiator LSR can automatically generate the 679 same MPLS echo request with different Reply Mode value to those nodes 680 that timeout. However, such mechanism will result in extended time 681 for the entire operation to complete (i.e. multiple seconds to 682 multiple minutes). This is undesirable, and perhaps unacceptable if 683 the "user" is an application. 685 With the extension described in this document, same procedures can be 686 performed with the Reply Mode Order TLV carrying {5, 2}. When LSP 687 Traceroute is issued, then following output may be displayed without 688 any unnecessary timeout. 690 Success (Reply Mode: 5) 691 Success (Reply Mode: 2) 692 Success (Reply Mode: 2) 693 Success (Reply Mode: 5) 694 Success (Reply Mode: 5) 695 Complete 697 Authors' Addresses 699 Nobo Akiya 700 Big Switch Networks 702 Email: nobo.akiya.dev@gmail.com 704 George Swallow 705 Cisco Systems 707 Email: swallow@cisco.com 709 Carlos Pignataro 710 Cisco Systems 712 Email: cpignata@cisco.com 714 Loa Andersson 715 Huawei 717 Email: loa@mail01.huawei.com 719 Mach(Guoyi) Chen 720 Huawei 722 Email: mach.chen@huawei.com