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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) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 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: November 2, 2015 Cisco Systems 7 L. Andersson 8 M. Chen 9 Huawei 10 May 1, 2015 12 Label Switched Path (LSP) Ping/Traceroute Reply Mode Simplification 13 draft-ietf-mpls-lsp-ping-reply-mode-simple-03 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 "Reply via 20 Specified Path (5)" Reply Mode value to easily indicate the reverse 21 LSP. This document also adds an optional TLV which can carry ordered 22 list of Reply Mode values. 24 This document updates RFC7110. 26 Requirements Language 28 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 29 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 30 document are to be interpreted as described in RFC 2119 [RFC2119]. 32 Status of This Memo 34 This Internet-Draft is submitted in full conformance with the 35 provisions of BCP 78 and BCP 79. 37 Internet-Drafts are working documents of the Internet Engineering 38 Task Force (IETF). Note that other groups may also distribute 39 working documents as Internet-Drafts. The list of current Internet- 40 Drafts is at http://datatracker.ietf.org/drafts/current/. 42 Internet-Drafts are draft documents valid for a maximum of six months 43 and may be updated, replaced, or obsoleted by other documents at any 44 time. It is inappropriate to use Internet-Drafts as reference 45 material or to cite them other than as "work in progress." 47 This Internet-Draft will expire on November 2, 2015. 49 Copyright Notice 51 Copyright (c) 2015 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (http://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the Simplified BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 67 2. Problem Statements . . . . . . . . . . . . . . . . . . . . . 3 68 3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 5 69 3.1. Reply via Specified Path Update . . . . . . . . . . . . . 5 70 3.2. Reply Mode Order TLV . . . . . . . . . . . . . . . . . . 6 71 4. Relations to Other LSP Ping/Trace Features . . . . . . . . . 7 72 4.1. Reply Path TLV . . . . . . . . . . . . . . . . . . . . . 7 73 4.1.1. Example 1: Reply Mode Order TLV Usage with Reply Path 74 TLV . . . . . . . . . . . . . . . . . . . . . . . . . 8 75 4.1.2. Example 2: Reply Mode Order TLV Usage with Reply Path 76 TLV . . . . . . . . . . . . . . . . . . . . . . . . . 8 77 4.2. Proxy LSP Ping . . . . . . . . . . . . . . . . . . . . . 9 78 4.2.1. Proxy LSR Sending an MPLS Echo Request . . . . . . . 9 79 4.2.2. Proxy LSR Sending an MPLS Proxy Ping Reply . . . . . 9 80 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 81 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 82 6.1. New Reply Mode Order TLV . . . . . . . . . . . . . . . . 10 83 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 84 8. Contributing Authors . . . . . . . . . . . . . . . . . . . . 10 85 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 86 9.1. Normative References . . . . . . . . . . . . . . . . . . 10 87 9.2. Informative References . . . . . . . . . . . . . . . . . 11 88 Appendix A. Reply Mode Order TLV Beneficial Scenarios . . . . . 11 89 A.1. Incorrect Forwarding Scenario . . . . . . . . . . . . . . 11 90 A.2. Non-Co-Routed Bidirectional LSP Scenario . . . . . . . . 12 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 93 1. Introduction 95 The MPLS LSP Ping, described in [RFC4379], allows an initiator LSR to 96 encode instructions (Reply Mode) on how a responder LSR should send 97 the response back to the initiator LSR. [RFC7110] also allows the 98 initiator LSR to encode a TLV (Reply Path TLV) which can instruct the 99 responder LSR to use specific LSP to send the response back to the 100 initiator LSR. Both approaches are powerful as they provide the 101 ability for the initiator LSR to control the return path. 103 However, it is becoming increasingly difficult for an initiator LSR 104 to select a valid return path to encode in the MPLS LSP echo request 105 packets. If the initiator LSR does not select a valid return path, 106 the MPLS LSP echo reply will not get back to the initiator LSR. This 107 results in a false failure of MPLS LSP Ping and Traceroute operation. 108 In an effort to minimize such false failures, different 109 implementations have chosen different default return path encoding 110 for different LSP types and LSP operations. The problem with 111 implementations having different default return path encoding is that 112 the MPLS echo reply will not work in many cases, and the default 113 value may not be the preferred choice by the operators. 115 This document describes: 117 o In Section 2, further description of the problems; 119 o In Section 3, a solution to minimize false failures while 120 accommodating operator preferences; 122 o In Section 4, relationships to other LSP Ping/Traceroute features; 124 o In Appendix A, examples of scenarios where the mechanism described 125 in this document provides benefits. 127 This documents updates [RFC7110] by allowing the usage of the Reply 128 Mode value 5 (Reply via Specified Path) without including the Reply 129 Path TLV. 131 2. Problem Statements 133 It is becoming increasingly difficult for implementations to 134 automatically supply a workable return path encoding for all MPLS LSP 135 Ping and Traceroute operations across all LSP types. There are 136 several factors which are contributing to this complication. 138 o Some LSPs have a control-channel, and some do not. Some LSPs have 139 a reverse LSP, and some do not. Some LSPs have IP reachability in 140 the reverse direction, and some do not. 142 o LSRs on some LSPs can have different available return path(s). 143 Available return path(s) can depend on whether the responder LSR 144 is a transit LSR or an egress LSR. In case of a bi-directional 145 LSP, available return path(s) on transit LSRs can also depend on 146 whether LSP is completely co-routed, partially co-routed or 147 associated (i.e., LSPs in the two directions are not co-routed). 149 o MPLS echo request packets may incorrectly terminate on an 150 unintended target, which can have different available return 151 path(s) than the intended target. 153 o The MPLS LSP Ping operation is expected to terminate on egress 154 LSR. However, the MPLS LSP Ping operation with specific TTL 155 values and MPLS LSP Traceroute operation can terminate on both 156 transit LSR(s) and the egress LSR. 158 Except for the case where the responder LSR does not have an IP route 159 back to the initiator LSR, it is possible to use the "Reply via an 160 IPv4/IPv6 UDP packet (2)" Reply Mode value in all cases. However, 161 some operators are preferring control-channel and reverse LSP as 162 default return path if they are available, which is not always the 163 case. 165 When specific return path encoding is supplied by users or 166 applications, then there are no issues in choosing the return path 167 encoding. When specific return path encoding is not supplied by 168 users or applications, then implementations use extra logic to 169 compute, and sometimes guess, the default return path encodings. If 170 a responder LSR receives an MPLS echo request containing return path 171 instructions which cannot be accommodated due to unavailability, then 172 the responder LSR often drops such packets. This results in the 173 initiator LSR not receiving the MPLS LSP echo reply packets back. 174 This consequence may be acceptable for failure cases (e.g., broken 175 LSPs) where the MPLS echo request terminated on unintended target. 176 However, the initiator LSR not receiving back MPLS echo reply 177 packets, even when the intended target received and verified the 178 requests, is not desirable as false failures will be conveyed to 179 users. 181 Many operators prefer some return path(s) over others for specific 182 LSP types. To accommodate this, implementations may default to 183 operator preferred return path (or allow default return path to be 184 configured) for a specific operation. However, if the sender of MPLS 185 echo request knew that preferred return path will not be available at 186 the intended target node, then it is not very beneficial to use a 187 Reply Mode corresponding to preferred return path (i.e., the sender 188 of the MPLS echo request will not receive the MPLS echo reply in the 189 successful case). What would be beneficial, for a given operation, 190 is for the sender of the MPLS echo request to determine which return 191 path(s) can and cannot be used ahead of time. 193 This document adds one Reply Mode value to describe the reverse LSP, 194 and one optional TLV to describe an ordered list of reply modes. 195 Based on operational needs, the TLV can describe multiple Reply Mode 196 values in a preferred order to allow the responder LSR to use the 197 first available Reply Mode from the list. This eliminates the need 198 for the initiator LSR to compute, or sometimes guess, the default 199 return path encoding. And that will result in simplified 200 implementations across vendors, and result in improved usability to 201 fit operational needs. 203 3. Solution 205 This document updates "Reply via Specified Path (5)" Reply Mode to 206 easily indicate the reverse LSP. This document also adds an optional 207 TLV which can carry ordered list of reply modes. 209 3.1. Reply via Specified Path Update 211 Some LSP types are capable of having related LSP in reverse 212 direction, through signaling or other association mechanisms. 213 Examples of such LSP types are RSVP LSPs and TP LSPs. This document 214 uses the term "Reverse LSP" to refer to the LSP in reverse direction 215 of such LSP types. Note that this document restricts the scope of 216 "Reverse LSP" applicability to those reverse LSPs which are capable 217 and allowed to carry the IP encapsulated MPLS echo reply. 219 [RFC7110] has defined the Reply Mode "Reply via Specified Path (5)" 220 which allows the initiator LSR to instruct the responder LSR to send 221 the MPLS echo reply message on the reverse LSP. However, the 222 instruction also requires the initiator LSR to include the "Reply 223 Path TLV" with the B bit (Bidirectional bit) set in the Flags field. 224 Additionally, [RFC7110] defines the usage of the "Reply via Specified 225 Path (5)" Reply Mode without inclusion of the "Reply Path TLV" to be 226 invalid. 228 This document updates the "Reply via Specified Path (5)" Reply Mode 229 as follows: 231 o The usage of the "Reply via Specified Path (5)" without inclusion 232 of a "Reply Path TLV" is no longer invalid. 234 o The usage of the "Reply via Specified Path (5)" without inclusion 235 of a "Reply Path TLV" implies the reverse LSP. In other words, 236 the usage of the "Reply via Specified Path (5)" without inclusion 237 of a "Reply Path TLV" has the same semantics as the usage of the 238 "Reply via Specified Path (5)" with inclusion of a "Reply Path 239 TLV" with the B bit set in the Flags field. 241 Note that the reverse LSP is in relation to the last FEC specified in 242 the Target FEC Stack TLV. 244 When a responder LSR is using this Reply Mode, transmitting MPLS echo 245 reply packet MUST use IP destination address of 127/8 for IPv4 and 246 0:0:0:0:0:FFFF:7F00/104 for IPv6. 248 3.2. Reply Mode Order TLV 250 This document also introduces a new optional TLV to describe list of 251 Reply Mode values. The new TLV will contain one or more Reply Mode 252 value(s) in preferred order. The first Reply Mode value is the most 253 preferred and the last Reply Mode value is the least preferred. 254 Following rules apply when using Reply Mode Order TLV. 256 1. The Reply Mode Order TLV MUST NOT be included in MPLS echo reply. 257 If the initiator LSR receives an MPLS echo reply with the Reply 258 Mode Order TLV, the initiator LSR MUST ignore the whole Reply 259 Mode Order TLV and MUST only use the value from the Reply Mode 260 field of the received MPLS echo reply. It may be beneficial for 261 implementations to provide counters and/or loggings, with 262 appropriate log dampening, to record this error case. 264 2. The Reply Mode Order TLV MAY be included in MPLS echo request. 266 3. The Reply Mode field of an MPLS echo request MUST be set to a 267 valid value even when supplying the Reply Mode Order TLV. The 268 initiator LSR SHOULD set the Reply Mode field of MPLS echo 269 request to a value that corresponds to a return path which most 270 likely to be available, in case the responder LSR does not 271 understand the Reply Mode Order TLV. 273 4. If a responder LSR understands the Reply Mode Order TLV but the 274 TLV is not valid (due to conditions described in the items 6, 7, 275 8 and 9 immediately below), then the responder LSR MUST ignore 276 the whole Reply Mode Order TLV and MUST only use the value from 277 the Reply Mode field of the received MPLS echo request. It may 278 be beneficial for implementations to provide counters and/or 279 loggings, with appropriate log dampening, to record this error 280 case. 282 5. If a responder LSR understands the Reply Mode Order TLV and the 283 TLV is valid, then the responder LSR MUST consider the Reply Mode 284 values described in the TLV and MUST NOT use the value described 285 in the Reply Mode field of received MPLS echo request. In other 286 words, a valid Reply Mode Order TLV overrides the value specified 287 in the Reply Mode field of received MPLS echo request. 289 6. Reply Mode Order TLV MUST contain at least one Reply Mode value. 291 7. A Reply Mode value, except for Reply Mode value 5 (Reply via 292 Specified Path), MUST NOT be repeated (i.e., MUST NOT appear 293 multiple times) in the Reply Mode Order TLV. 295 8. The Reply Mode value 5 (Reply via Specified Path) MAY be included 296 more than once in the Reply Mode Order TLV. However, in such 297 case a Reply Path TLV MUST be included for all instances of the 298 Reply Mode value 5 included in the Reply Mode Order TLV. In 299 other words, 3 instances of the Reply Mode value 5 in the Reply 300 Mode Order TLV will require 3 instances of the Reply Path TLVs. 302 9. The Reply Mode value 1 (Do not reply) MUST NOT be used in the 303 Reply Mode Order TLV. 305 The responder LSR is to select the first available return path in 306 this TLV. Reply Mode value corresponding to the selected return path 307 MUST be set in Reply Mode field of MPLS echo reply to communicate 308 back to the initiator LSR which return path was chosen. 310 The format of the TLV is as follows: 312 0 1 2 3 313 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 1 314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 315 | Reply Mode Order TLV Type | Length | 316 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 317 ~ Reply mode 1 | Reply mode 2 | Reply mode 3 | Reply mode 4 ~ 318 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 319 Figure 1 Reply Mode Order TLV 321 This is a variable length optional TLV. Each Reply Mode field is 1 322 octet. 324 4. Relations to Other LSP Ping/Trace Features 326 4.1. Reply Path TLV 328 [RFC7110] has defined that the "Reply Path TLV" can include Sub-TLVs 329 describing multiple FECs, from which the responder LSR can choose the 330 FEC to send the MPLS echo reply message. [RFC7110] has also defined 331 that Sub-TLVs, within the "Reply Path TLV", describing FECs for 332 return paths SHOULD be ignored when the B bit is set in the Flags 333 field. Therefore, when the initiator LSR wants to use the Reply Mode 334 Order TLV to describe the reverse LSP and other FECs for return 335 paths, then the initiator SHOULD include two "Reply via Specified 336 Path (5)" Reply Mode values and two "Reply Path TLV" objects (one 337 "Reply Path TLV" corresponding to each "Reply via Specified Path 338 (5)"). 340 o The reverse LSP is described by the "Reply via Specified Path (5)" 341 Reply Mode value and the corresponding "Reply Path TLV" with the B 342 bit set in the Flags field. In this "Reply Path TLV", no Sub-TLVs 343 are present. 345 o Other return FECs are described by the "Reply via Specified Path 346 (5)" Reply Mode value and the corresponding "Reply Path TLV" 347 describing the FECs for return paths. In this "Reply Path TLV", 348 the B bit is cleared in the Flags field. 350 4.1.1. Example 1: Reply Mode Order TLV Usage with Reply Path TLV 352 If the initiator LSR was interested in encoding following return 353 paths: 355 1. Reply via application level control channel 357 2. FEC X 359 3. FEC Y 361 4. Reply via an IPv4/IPv6 UDP packet 363 Then the MPLS echo request message is to carry: 365 o The Reply Mode Order TLV carrying Reply Modes {4, 5, 2} 367 o The Reply Path TLV carrying {FEC X, FEC Y} 369 Described encoding of the Reply Mode Order TLV and the Reply Path TLV 370 in the MPLS echo request message will result in the responder LSR to 371 prefer "Reply via application level control channel (4)", followed by 372 FEC X, FEC Y and then "Reply via an IPv4/IPv6 UDP packet (2)". 374 4.1.2. Example 2: Reply Mode Order TLV Usage with Reply Path TLV 376 If the initiator LSR was interested in encoding following return 377 paths: 379 1. Reverse LSP 381 2. Reply via an IPv4/IPv6 UDP packet 382 3. FEC X 384 4. FEC Y 386 Then the MPLS echo request message is to carry: 388 o The Reply Mode Order TLV carrying Reply Modes {5, 2, 5} 390 o One Reply Path TLV with the B bit set. 392 o One Reply Path TLV carrying {FEC X, FEC Y} 394 Described encoding of the Reply Mode Order TLV and the Reply Path TLV 395 in the MPLS echo request message will result in the responder LSR to 396 prefer the reverse LSP, followed by "Reply via an IPv4/IPv6 UDP 397 packet (2)", FEC X and then FEC Y. 399 4.2. Proxy LSP Ping 401 The mechanism defined in this document will work with Proxy LSP Ping 402 defined by [I-D.ietf-mpls-proxy-lsp-ping]. The MPLS proxy ping 403 request message can carry a Reply Mode value in the header and one or 404 more Reply Mode values in the Reply Mode Order TLV. It is 405 RECOMMENDED that the Reply Mode 2 (Reply via an IPv4/IPv6 UDP packet) 406 be used in the Reply Mode field of the MPLS proxy ping request 407 message. 409 4.2.1. Proxy LSR Sending an MPLS Echo Request 411 If the proxy LSR is sending an MPLS echo request, then the proxy LSR 412 MUST copy following elements from the MPLS proxy ping request message 413 to the MPLS echo request message. 415 o The Reply Mode field. 417 o The Reply Mode Order TLV. 419 o The Reply Path TLV(s). If there are more than one Reply Path 420 TLVs, then then order of them MUST be preserved when copying. 422 4.2.2. Proxy LSR Sending an MPLS Proxy Ping Reply 424 If the proxy LSR is sending an MPLS proxy ping reply, then it is 425 RECOMMENDED that the Reply Mode Order TLV be ignored and the Reply 426 Mode field in the MPLS proxy ping request message be used. 428 5. Security Considerations 430 Beyond those specified in [RFC4379] and [RFC7110], there are no 431 further security measures required. 433 6. IANA Considerations 435 6.1. New Reply Mode Order TLV 437 IANA is requested to assign a new TLV type value from the "TLVs" sub- 438 registry within the "Multiprotocol Label Switching Architecture 439 (MPLS)" registry, for the "Reply Mode Order TLV". 441 The new TLV Type value should be assigned from the range 442 (32768-49161) specified in [RFC4379] section 3 that allows the TLV 443 type to be silently dropped if not recognized. 445 Type Meaning Reference 446 ---- ------- --------- 447 TBD1 Reply Mode Order TLV this document 449 7. Acknowledgements 451 Authors would like to thank Santiago Alvarez and Faisal Iqbal for 452 discussions which motivated creation of this document. Authors would 453 also like to thank Sam Aldrin, Curtis Villamizar, Ross Callon, 454 Jeffrey Zhang, Jeremy Whittaker, Mustapha Alissaoui, Qin Wu, Jie Dong 455 and Adrian Farrel for providing valuable comments to influence the 456 contents of the draft. 458 8. Contributing Authors 460 Shaleen Saxena 461 Brocade 462 Email: ssaxena@brocade.com 464 9. References 466 9.1. Normative References 468 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 469 Requirement Levels", BCP 14, RFC 2119, March 1997. 471 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 472 Label Switched (MPLS) Data Plane Failures", RFC 4379, 473 February 2006. 475 [RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord, 476 "Return Path Specified Label Switched Path (LSP) Ping", 477 RFC 7110, January 2014. 479 9.2. Informative References 481 [I-D.ietf-mpls-proxy-lsp-ping] 482 Swallow, G., Lim, V., and S. Aldrin, "Proxy MPLS Echo 483 Request", draft-ietf-mpls-proxy-lsp-ping-05 (work in 484 progress), March 2015. 486 Appendix A. Reply Mode Order TLV Beneficial Scenarios 488 This section lists examples of how the Reply Mode Order TLV can 489 benefit. 491 A.1. Incorrect Forwarding Scenario 493 A network has a following LSP, and the LSP has a control channel. 495 A------B------C------D------E 496 | 497 | 498 F 500 Forward Paths: A-B-C-D-E 502 Figure 2: Incorrect Forwarding 504 Imagine that D is incorrectly label switching to F (instead of E). 505 In this scenario, LSP Traceroute with "Reply via application level 506 control channel (4)" will result in following result. 508 Success (Reply from B) 509 Success (Reply from C) 510 Success (Reply from D) 511 Timeout... 512 Complete 514 This is because F does not have a control channel to send the MPLS 515 echo reply message. With the extension described in this document, 516 same procedures can be performed with the Reply Mode Order TLV 517 carrying {4, 2}. When LSP Traceroute is issued, then following output 518 may be displayed without any unnecessary timeout. 520 Success (Reply from B, Reply Mode: 4) 521 Success (Reply from C, Reply Mode: 4) 522 Success (Reply from D, Reply Mode: 4) 523 FEC Mismatch (Reply from F, Reply Mode: 2) 524 Complete 526 The result provides more diagnostic information to the initiator LSR, 527 and without any delay (i.e. timeout from one or more downstream 528 LSRs). 530 A.2. Non-Co-Routed Bidirectional LSP Scenario 532 A network has a following bidirectional LSP where the forward LSP and 533 the reverse LSP are not fully co-routed. 535 +----C------D----+ 536 / \ 537 A------B G------H 538 \ / 539 +----E------F----+ 541 Forward Paths: A-B-C-D-G-H (upper path) 542 Reverse Paths: H-G-F-E-B-A (lower path) 544 Figure 3: Non-Co-Routed Bidirectional LSP 546 Some operators may prefer and configure the system to default the 547 Reply Mode to indicate the reverse LSP when MPLS echo request 548 messages are sent on bidirectional LSPs. Without extensions 549 described in this document, following behaviors will be seen: 551 o When LSP Ping is issued from A, reply will come back on the 552 reverse LSP from H. 554 o When LSP Traceroute is issued from A, reply will come back on the 555 reverse LSP from B, G and H, but will encounter a timeout from C 556 and D as there are no reverse LSP on those nodes. 558 o When LSP Ping with specific TTL value is issued from A, whether a 559 timeout will be encountered depends on the value of the TTL used 560 (i.e. whether or not MPLS echo request terminates on a node that 561 has reverse LSP). 563 One can argue that the initiator LSR can automatically generate a 564 same MPLS echo request with different Reply Mode value to those nodes 565 that timeout. However, such mechanism will result in extended time 566 for the entire operation to complete (i.e. multiple seconds to 567 multiple minutes). This is undesirable, and perhaps unacceptable if 568 the "user" is an application. 570 With the extension described in this document, same procedures can be 571 performed with the Reply Mode Order TLV carrying {5, 2}. When LSP 572 Traceroute is issued, then following output may be displayed without 573 any unnecessary timeout. 575 Success (Reply Mode: 5) 576 Success (Reply Mode: 2) 577 Success (Reply Mode: 2) 578 Success (Reply Mode: 5) 579 Success (Reply Mode: 5) 580 Complete 582 Authors' Addresses 584 Nobo Akiya 585 Big Switch Networks 587 Email: nobo.akiya.dev@gmail.com 589 George Swallow 590 Cisco Systems 592 Email: swallow@cisco.com 594 Carlos Pignataro 595 Cisco Systems 597 Email: cpignata@cisco.com 599 Loa Andersson 600 Huawei 602 Email: loa@mail01.huawei.com 604 Mach(Guoyi) Chen 605 Huawei 607 Email: mach.chen@huawei.com