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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) ** Obsolete normative reference: RFC 6424 (Obsoleted by RFC 8029) ** Obsolete normative reference: RFC 7537 (Obsoleted by RFC 8029) Summary: 3 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MPLS Working Group N. Akiya 3 Internet-Draft Big Switch Networks 4 Updates: 6790 (if approved) G. Swallow 5 Intended status: Standards Track C. Pignataro 6 Expires: March 9, 2017 Cisco 7 A. Malis 8 Huawei Technologies 9 S. Aldrin 10 Google 11 September 5, 2016 13 Label Switched Path (LSP) and Pseudowire (PW) Ping/Trace over 14 MPLS Network using Entropy Labels (EL) 15 draft-ietf-mpls-entropy-lsp-ping-05 17 Abstract 19 Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) Ping 20 and Traceroute are methods used to test Equal-Cost Multipath (ECMP) 21 paths. Ping is known as a connectivity verification method and 22 Traceroute as a fault isolation method, as described in RFC 4379. 23 When an LSP is signaled using the Entropy Label (EL) described in RFC 24 6790, the ability for LSP Ping and Traceroute operations to discover 25 and exercise ECMP paths is lost for scenarios where Label Switching 26 Routers (LSRs) apply different load balancing techniques. One such 27 scenario is when some LSRs apply EL-based load balancing while other 28 LSRs apply non-EL-based load balancing (e.g., IP). Another scenario 29 is when an EL-based LSP is stitched with another LSP which can be EL- 30 based or non-EL-based. 32 This document extends the MPLS LSP Ping and Traceroute multipath 33 mechanisms in RFC 6424 to allow the ability of exercising LSPs which 34 make use of the EL. This document updates RFC 6790. 36 Requirements Language 38 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 39 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 40 document are to be interpreted as described in RFC 2119 [RFC2119]. 42 Status of This Memo 44 This Internet-Draft is submitted in full conformance with the 45 provisions of BCP 78 and BCP 79. 47 Internet-Drafts are working documents of the Internet Engineering 48 Task Force (IETF). Note that other groups may also distribute 49 working documents as Internet-Drafts. The list of current Internet- 50 Drafts is at http://datatracker.ietf.org/drafts/current/. 52 Internet-Drafts are draft documents valid for a maximum of six months 53 and may be updated, replaced, or obsoleted by other documents at any 54 time. It is inappropriate to use Internet-Drafts as reference 55 material or to cite them other than as "work in progress." 57 This Internet-Draft will expire on March 9, 2017. 59 Copyright Notice 61 Copyright (c) 2016 IETF Trust and the persons identified as the 62 document authors. All rights reserved. 64 This document is subject to BCP 78 and the IETF Trust's Legal 65 Provisions Relating to IETF Documents 66 (http://trustee.ietf.org/license-info) in effect on the date of 67 publication of this document. Please review these documents 68 carefully, as they describe your rights and restrictions with respect 69 to this document. Code Components extracted from this document must 70 include Simplified BSD License text as described in Section 4.e of 71 the Trust Legal Provisions and are provided without warranty as 72 described in the Simplified BSD License. 74 Table of Contents 76 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 77 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 78 1.2. Background . . . . . . . . . . . . . . . . . . . . . . . 4 79 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5 80 3. Multipath Type 9 . . . . . . . . . . . . . . . . . . . . . . 7 81 4. Pseudowire Tracing . . . . . . . . . . . . . . . . . . . . . 7 82 5. Entropy Label FEC . . . . . . . . . . . . . . . . . . . . . . 8 83 6. DS Flags: L and E . . . . . . . . . . . . . . . . . . . . . . 9 84 7. New Multipath Information Type: TBD4 . . . . . . . . . . . . 10 85 8. Initiating LSR Procedures . . . . . . . . . . . . . . . . . . 11 86 9. Responder LSR Procedures . . . . . . . . . . . . . . . . . . 13 87 9.1. IP-based Load Balancer & Not Pushing ELI/EL . . . . . . . 14 88 9.2. IP Based Load Balancer & Pushes ELI/EL . . . . . . . . . 14 89 9.3. Label-based Load Balancer & Not Pushing ELI/EL . . . . . 15 90 9.4. Label-based Load Balancer & Pushes ELI/EL . . . . . . . . 16 91 9.5. Flow-Aware MS-PW Stitching LSR . . . . . . . . . . . . . 17 92 10. Supported and Unsupported Cases . . . . . . . . . . . . . . . 17 93 11. Security Considerations . . . . . . . . . . . . . . . . . . . 19 94 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 95 12.1. Entropy Label FEC . . . . . . . . . . . . . . . . . . . 19 96 12.2. DS Flags . . . . . . . . . . . . . . . . . . . . . . . . 19 97 12.3. Multipath Type . . . . . . . . . . . . . . . . . . . . . 20 98 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20 99 14. Contributing Authors . . . . . . . . . . . . . . . . . . . . 20 100 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 101 15.1. Normative References . . . . . . . . . . . . . . . . . . 20 102 15.2. Informative References . . . . . . . . . . . . . . . . . 21 103 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 105 1. Introduction 107 1.1. Terminology 109 The following acronyms and terms are used in this document: 111 o MPLS - Multiprotocol Label Switching. 113 o LSP - Label Switched Path. 115 o Stitched LSP - Stitched Label Switched Paths combine several LSPs 116 such that a single end-to-end (e2e) LSP is realized. [RFC6424] 117 describes LSP Ping for Stitched LSPs. 119 o LSR - Label Switching Router. 121 o FEC - Forwarding Equivalence Class. 123 o ECMP - Equal-Cost Multipath. 125 o EL - Entropy Label. 127 o ELI - Entropy Label Indicator. 129 o GAL - Generic Associated Channel Label. 131 o MS-PW - Multi-Segment Pseudowire. 133 o Initiating LSR - LSR which sends an MPLS echo request. 135 o Responder LSR - LSR which receives an MPLS echo request and sends 136 an MPLS echo reply. 138 o IP-Based Load Balancer - LSR which load balances on fields from an 139 IP header (and possibly fields from upper layers), and does not 140 consider an entropy label from an MPLS label stack (i.e., flow 141 label [RFC6391] or entropy label [RFC6790]) for load balancing 142 purposes. 144 o Label-Based Load Balancer - LSR which load balances on an entropy 145 label from an MPLS label stack (i.e., flow label or entropy 146 label), and does not consider fields from an IP header (and 147 possibly fields from upper layers) for load balancing purposes. 149 o Label and IP-Based Load Balancer - LSR which load balances on both 150 entropy labels from an MPLS label stack and fields from an IP 151 header (and possibly fields from upper layers). 153 1.2. Background 155 MPLS implementations employ a wide variety of load balancing 156 techniques in terms of fields used for hash "keys". The mechanisms 157 in [RFC4379] and updated by [RFC6424] are designed to provide 158 multipath support for a subset of techniques. The intent of this 159 document is to provide multipath support for the supported techniques 160 which are compromised by the use of ELs [RFC6790]. Section 10 161 describes supported and unsupported cases, and it may be useful for 162 the reader to first review this section. 164 The Downstream Detailed Mapping (DDMAP) TLV [RFC6424] provides 165 Multipath Information which can be used by an LSP Ping initiator to 166 trace and validate ECMP paths between an ingress and egress. The 167 Multipath Information encodings defined by [RFC6424] are sufficient 168 when all the LSRs along the path(s), between ingress and egress, 169 consider the same set of "keys" as input for load balancing 170 algorithms, e.g., either all IP-based or all label-based. 172 With the introduction of [RFC6790], some LSRs may perform load 173 balancing based on labels while others may be IP-based. This results 174 in an LSP Ping initiator that is unable to trace and validate all the 175 ECMP paths in the following scenarios: 177 o One or more transit LSRs along an LSP with ELI/EL in the label 178 stack do not perform ECMP load balancing based on EL (hashes based 179 on "keys" including the IP destination address). This scenario is 180 not only possible but quite common due to transit LSRs not 181 implementing [RFC6790] or transit LSRs implementing [RFC6790], but 182 not implementing the suggested transit LSR behavior in Section 4.3 183 of [RFC6790]. 185 o Two or more LSPs stitched together with at least one of these LSPs 186 pushing ELI/EL into the label stack. 188 These scenarios can be quite common because deployments of [RFC6790] 189 typically have a mixture of nodes that support ELI/EL and nodes that 190 do not. There will also typically be a mixture of areas that support 191 ELI/EL and areas that do not. 193 As pointed out in [RFC6790], the procedures of [RFC4379] (and 194 consequently of [RFC6424]) with respect to Multipath Information Type 195 {9} are incomplete. However, [RFC6790] does not actually update 196 [RFC4379]. Further, the specific EL location is not clearly defined, 197 particularly in the case of Flow Aware Pseudowires [RFC6391]. This 198 document defines a new FEC Stack sub-TLV for the entropy label. 199 Section 3 of this document updates the procedures for Multipath 200 Information Type {9} described in [RFC4379] and applicable to 201 [RFC6424]. The rest of this document describes extensions required 202 to restore ECMP discovery and tracing capabilities for the scenarios 203 described. 205 [RFC4379], [RFC6424], and this document will support IP-based load 206 balancers and label-based load balancers which limit their hash to 207 the first (top-most) or only entropy label in the label stack. Other 208 use cases (refer to Section 10) are out of scope. 210 2. Overview 212 [RFC4379] describes LSP traceroute as an operation where the 213 initiating LSR sends a series of MPLS echo requests towards the same 214 destination. The first packet in the series has the TTL set to 1. 215 When the echo reply is received from the LSR one hop away, the second 216 echo request in the series is sent with the TTL set to 2. For each 217 additional echo request the TLL is incremented by one until a 218 response is received from the intended destination. The initiating 219 LSR discovers and exercises ECMP by obtaining Multipath Information 220 from each transit LSR and using a specific destination IP address or 221 specific entropy label. 223 From here on, the notation {x, y, z} refers to Multipath Information 224 Types x, y, or z. Multipath Information Types are defined in 225 Section 3.3 of [RFC4379]. 227 The LSR initiating LSP Ping sends an MPLS echo request with Multipath 228 Information. This Multipath Information is described in the echo 229 request's DDMAP TLV, and may contain a set of IP addresses or a set 230 of labels. Multipath Information Types {2, 4, 8} carry a set of IP 231 addresses, and Multipath Information Type {9} carries a set of 232 labels. The responder LSR (the receiver of the MPLS echo request) 233 will determine the subset of initiator-specified Multipath 234 Information which load balances to each downstream (outgoing) 235 interface. The responder LSR sends an MPLS echo reply with resulting 236 Multipath Information per downstream (outgoing interface) back to the 237 initiating LSR. The initiating LSR is then able to use a specific IP 238 destination address or a specific label to exercise a specific ECMP 239 path on the responder LSR. 241 The current behavior is problematic in the following scenarios: 243 o The initiating LSR sends IP Multipath Information, but the 244 responder LSR load balances on labels. 246 o The initiating LSR sends Label Multipath Information, but the 247 responder LSR load balances on IP addresses. 249 o The initiating LSR sends existing Multipath Information to an LSR 250 which pushes ELI/EL in the label stack, but the initiating LSR can 251 only continue to discover and exercise specific paths of the ECMP, 252 if the LSR which pushes ELI/EL responds with both IP addresses and 253 the associated EL corresponding to each IP address. This is 254 because: 256 * An ELI/EL-pushing LSR that is a stitching point will load 257 balance based on the IP address. 259 * Downstream LSR(s) of an ELI/EL-pushing LSR may load balance 260 based on ELs. 262 o The initiating LSR sends existing Multipath Information to an ELI/ 263 EL-pushing LSR, but the initiating LSR can only continue to 264 discover and exercise specific paths of ECMP, if the ELI/EL- 265 pushing LSR responds with both labels and the associated EL 266 corresponding to the label. This is because: 268 * An ELI/EL-pushing LSR that is a stitching point will load 269 balance based on the EL from the previous LSP and pushes a new 270 EL. 272 * Downstream LSR(s) of ELI/EL-pushing LSR may load balance based 273 on new ELs. 275 The above scenarios demonstrate the existing Multipath Information is 276 insufficient when LSP traceroute is used on an LSP with entropy 277 labels [RFC6790]. This document defines a new Multipath Information 278 Type to be used in the DDMAP of MPLS echo request/reply packets for 279 [RFC6790] LSPs. 281 The responder LSR can reply with empty Multipath Information if no IP 282 address is set or label set is received with the Multipath 283 Information. An empty return is also possible if an initiating LSR 284 sends Multipath Information of one type, IP Address or Label, but the 285 responder LSR load balances on the other type. To disambiguate 286 between the two results, this document introduces new flags in the 287 DDMAP TLV to allow the responder LSR to describe the load balancing 288 technique being used. 290 To use this enhanced method end-to-end, all LSRs along the LSP need 291 to be able to understand the new flags and the new Multipath 292 Information Type. Mechanisms to verify this condition are outside of 293 the scope of this document. The rest of the requirements are 294 detailed in the initiating LSR and responder LSR procedures. Two 295 additional DS Flags are defined for the DDMAP TLV in Section 6. 296 These two flags are used by the responder LSR to describe its load 297 balance behavior on a received MPLS echo request. 299 Note that the terms "IP-Based Load Balancer" and "Label-Based Load 300 Balancer" are in context of how a received MPLS echo request is 301 handled by the responder LSR. 303 3. Multipath Type 9 305 [RFC4379] defined Multipath Type {9} for tracing of LSPs where label- 306 based load balancing is used. However, as pointed out in [RFC6790], 307 the procedures for using this type are incomplete as the specific 308 location of the label was not defined. It was assumed that the 309 presence of Multipath Type {9} implied the value of the bottom-of- 310 stack label should be varied by the values indicated by multipath to 311 determine the respective outgoing interfaces. 313 Section 5 defines a new FEC-Stack sub-TLV to indicate an entropy 314 label. These labels MAY appear anywhere in a label stack. 316 Multipath Type {9} applies to the first label in the label stack that 317 corresponds to an EL-FEC. If no such label is found, it applies to 318 the label at the bottom of the label stack. 320 4. Pseudowire Tracing 322 This section defines procedures for tracing pseudowires. These 323 procedures pertain to the use of Multipath Information Type {9} as 324 well as Type {TBD4}. In all cases below, when a control word is in 325 use, the N-flag in the DDMAP MUST be set. Note that when a control 326 word is not in use, the returned DDMAPs may not be accurate. 328 In order to trace a non-flow-aware Pseudowire, the initiator includes 329 an EL-FEC instead of the appropriate PW FEC at the bottom of the FEC 330 stack. Tracing in this way will cause compliant routers to return 331 the proper outgoing interface. Note that this procedure only traces 332 to the end of the MPLS LSP that is under test and will not verify the 333 PW FEC. To actually verify the PW FEC or in the case of a MS-PW, to 334 determine the next pseudowire label value, the initiator MUST repeat 335 that step of the trace (i.e., repeating the TTL value used) but with 336 the FEC Stack modified to contain the appropriate PW FEC. Note that 337 these procedures are applicable to scenarios where an initiator is 338 able to vary the bottom label (i.e., Pseudowire label). Possible 339 scenarios are tracing multiple non-flow-aware Pseudowires on the same 340 endpoints or tracing a non-flow-aware Pseudowire provisioned with 341 multiple Pseudowire labels. 343 In order to trace a flow-aware Pseudowire [RFC6391], the initiator 344 includes an EL FEC at the bottom of the FEC Stack and pushes the 345 appropriate PW FEC onto the FEC Stack. 347 In order to trace through non-compliant routers, the initiator forms 348 an MPLS echo request message and includes a DDMAP with Multipath Type 349 {9}. For a non-flow-aware Pseudowire it includes the appropriate PW 350 FEC in the FEC Stack. For a flow-aware Pseudowire, the initiator 351 includes a Nil FEC at the bottom of the FEC Stack and pushes the 352 appropriate PW FEC onto the FEC Stack. 354 5. Entropy Label FEC 356 The entropy label indicator (ELI) is a reserved label that has no 357 explicit FEC associated, and has label value 7 assigned from the 358 reserved range. Use the Nil FEC as the Target FEC Stack sub-TLV to 359 account for ELI in a Target FEC Stack TLV. 361 The entropy label (EL) is a special purpose label with the label 362 value being discretionary (i.e., the label value is not from the 363 reserved range). For LSP verification mechanics to perform its 364 purpose, it is necessary for a Target FEC Stack sub-TLV to clearly 365 describe the EL, particularly in the scenario where the label stack 366 does not carry ELI (e.g., flow-aware Pseudowire [RFC6391]). 367 Therefore, this document defines an EL FEC sub-TLV (TBD1, see 368 Section 12.1) to allow a Target FEC Stack sub-TLV to be added to the 369 Target FEC Stack to account for EL. 371 The Length is 4. Labels are 20-bit values treated as numbers. 373 0 1 2 3 374 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 1 375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 376 | Label | MBZ | 377 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 379 Figure 1: Entropy Label FEC 381 Label is the actual label value inserted in the label stack; the MBZ 382 field MUST be zero when sent and ignored on receipt. 384 6. DS Flags: L and E 386 Two flags, L and E, are added to the DS Flags field of the DDMAP TLV. 387 Both flags MUST NOT be set in echo request packets when sending, and 388 SHOULD be ignored when received. Zero, one or both new flags MUST be 389 set in echo reply packets. 391 DS Flags 392 -------- 394 0 1 2 3 4 5 6 7 395 +-+-+-+-+-+-+-+-+ 396 | MBZ |L|E|I|N| 397 +-+-+-+-+-+-+-+-+ 399 RFC-Editor-Note: Please update the above figure to place the flag E 400 in the bit number TBD2 and the flag L in the bit number TBD3. 402 Flag Name and Meaning 403 ---- ---------------- 404 L Label-based load balance indicator 405 This flag MUST be cleared in the echo request. An LSR 406 which performs load balancing on a label MUST set this 407 flag in the echo reply. An LSR which performs load 408 balancing on IP MUST NOT set this flag in the echo 409 reply. 411 E ELI/EL push indicator 412 This flag MUST be cleared in the echo request. An LSR 413 which pushes ELI/EL MUST set this flag in the echo 414 reply. An LSR which does not push ELI/EL MUST NOT set 415 this flag in the echo reply. 417 The two flags result in four load balancing techniques which the echo 418 reply generating LSR can indicate: 420 o {L=0, E=0} LSR load balances based on IP and does not push ELI/EL. 422 o {L=0, E=1} LSR load balances based on IP and pushes ELI/EL. 424 o {L=1, E=0} LSR load balances based on labels and does not push 425 ELI/EL. 427 o {L=1, E=1} LSR load balances based on labels and pushes ELI/EL. 429 7. New Multipath Information Type: TBD4 431 One new Multipath Information Type is added to be used in DDMAP TLV. 432 This new Multipath Type has the value of TBD4. 434 Key Type Multipath Information 435 --- ---------------- --------------------- 436 TBD4 IP and Label set IP addresses and label prefixes 438 Multipath Type TBD4 is comprised of three sections. The first 439 section describes the IP address set. The second section describes 440 the label set. The third section describes another label set which 441 associates to either the IP address set or the label set specified in 442 the other sections. 444 Multipath Information Type TBD4 has following format: 446 0 1 2 3 447 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 1 448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 |IPMultipathType| IP Multipath Length | Reserved(MBZ) | 450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 451 ~ ~ 452 | (IP Multipath Information) | 453 ~ ~ 454 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 455 |LbMultipathType| Label Multipath Length | Reserved(MBZ) | 456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 457 ~ ~ 458 | (Label Multipath Information) | 459 ~ ~ 460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 461 | Assoc Label Multipath Length | Reserved(MBZ) | 462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 463 ~ ~ 464 | (Associated Label Multipath Information) | 465 ~ ~ 466 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 468 Figure 2: Multipath Information Type TBD4 470 o IPMultipathType 472 * 0 when "IP Multipath Information" is omitted. Otherwise, one 473 of the IP Multipath Information values: {2, 4, 8}. 475 o IP Multipath Information 476 * This section is omitted when "IPMultipathType" is 0. 477 Otherwise, this section reuses IP Multipath Information from 478 [RFC4379]. Specifically, Multipath Information for values {2, 479 4, 8} can be used. 481 o LbMultipathType 483 * 0 when "Label Multipath Information" is omitted. Otherwise, 484 Label Multipath Information value {9}. 486 o Label Multipath Information 488 * This section is omitted when "LbMultipathType" is 0. 489 Otherwise, this section reuses Label Multipath Information from 490 [RFC4379]. Specifically, Multipath Information for value {9} 491 can be used. 493 o Associated Label Multipath Information 495 * "Assoc Label Multipath Length" is a 16-bit field of Multipath 496 Information which indicates the length in octets of the 497 Associated Label Multipath Information. 499 * "Associated Label Multipath Information" is a list of labels 500 with each label described in 24 bits. This section MUST be 501 omitted in an MPLS echo request message. A midpoint which 502 pushes ELI/EL labels SHOULD include "Assoc Label Multipath 503 Information" in its MPLS echo reply message, along with either 504 "IP Multipath Information" or "Label Multipath Information". 505 Each specified associated label described in this section maps 506 to a specific IP address OR label described in the "IP 507 Multipath Information" section or "Label Multipath Information" 508 section. For example, if three IP addresses are specified in 509 the "IP Multipath Information" section, then there MUST be 510 three labels described in this section. The first label maps 511 to the first IP address specified, the second label maps to the 512 second IP address specified, and the third label maps to the 513 third IP address specified. 515 When a section is omitted, the length for that section MUST be set to 516 zero. 518 8. Initiating LSR Procedures 520 The following procedure is described in terms of an EL_LSP boolean 521 maintained by the initiating LSR. This value controls the Multipath 522 Information Type to be used in the transmitted echo request packets. 523 When the initiating LSR is transmitting an echo request packet with 524 DDMAP with a non-zero Multipath Information Type, then the EL_LSP 525 boolean MUST be consulted to determine the Multipath Information Type 526 to use. 528 In addition to procedures described in [RFC4379], as updated by 529 Section 3 and [RFC6424], the initiating LSR MUST operate with the 530 following procedures: 532 o When the initiating LSR pushes ELI/EL, initialize EL_LSP=True. 533 Else set EL_LSP=False. 535 o When the initiating LSR is transmitting a non-zero Multipath 536 Information Type: 538 * If (EL_LSP), the initiating LSR MUST use Multipath Information 539 Type {TBD4} unless the responder LSR cannot handle Type {TBD4}. 540 When the initiating LSR is transmitting Multipath Information 541 Type {TBD4}, both "IP Multipath Information" and "Label 542 Multipath Information" MUST be included, and "Associated Label 543 Multipath Information" MUST be omitted (NULL). 545 * Else the initiating LSR MAY use Multipath Information Type {2, 546 4, 8, 9, TBD4}. When the initiating LSR is transmitting 547 Multipath Information Type {TBD4} in this case, "IP Multipath 548 Information" MUST be included, and "Label Multipath 549 Information" and "Associated Label Multipath Information" MUST 550 be omitted (NULL). 552 o When the initiating LSR receives an echo reply with {L=0, E=1} in 553 the DS flags with valid contents, set EL_LSP=True. 555 In the following conditions, the initiating LSR may have lost the 556 ability to exercise specific ECMP paths. The initiating LSR MAY 557 continue with "best effort" in the following cases: 559 o Received echo reply contains empty Multipath Information. 561 o Received echo reply contains {L=0, E=} DS flags, but does not 562 contain IP Multipath Information. 564 o Received echo reply contains {L=1, E=} DS flags, but does not 565 contain Label Multipath Information. 567 o Received echo reply contains {L=, E=1} DS flags, but does not 568 contain Associated Label Multipath Information. 570 o IP Multipath Information Types {2, 4, 8} sent, and received echo 571 reply with {L=1, E=0} in DS flags. 573 o Multipath Information Type {TBD4} sent, and received echo reply 574 with Multipath Information Type other than {TBD4}. 576 9. Responder LSR Procedures 578 Common Procedures: 580 o The responder LSR receiving an MPLS echo request packet MUST first 581 determine whether or not the initiating LSR supports this LSP Ping 582 and Traceroute extension for Entropy Labels. If either of the 583 following conditions are met, the responder LSR SHOULD determine 584 that the initiating LSR supports this LSP Ping and Traceroute 585 extension for entropy labels. 587 1. Received MPLS echo request contains the Multipath Information 588 Type {TBD4}. 590 2. Received MPLS echo request contains a Target FEC Stack TLV 591 that includes the entropy label FEC. 593 If the initiating LSR is determined not to support this LSP Ping 594 and Traceroute extension for entropy labels, then the responder 595 LSR MUST NOT follow further procedures described in this section. 596 Specifically, MPLS echo reply packets: 598 * MUST have the following DS Flags cleared (i.e., not set): "ELI/ 599 EL push indicator" and "Label-based load balance indicator". 601 * MUST NOT use Multipath Information Type {TBD4}. 603 o The responder LSR receiving an MPLS echo request packet with 604 Multipath Information Type {TBD4} MUST validate the following 605 contents. Any deviation MUST result in the responder LSR 606 considering the packet as malformed and returning code 1 607 ("Malformed echo request received") in the MPLS echo reply packet. 609 * IP Multipath Information MUST be included. 611 * Label Multipath Information MAY be included. 613 * Associated Label Multipath Information MUST be omitted (NULL). 615 The following subsections describe expected responder LSR procedures 616 when the echo reply is to include DDMAP TLVs, based on the local load 617 balance technique being employed. In case the responder LSR performs 618 deviating load balance techniques on a per downstream basis, 619 appropriate procedures matched to each downstream load balance 620 technique MUST be followed. 622 9.1. IP-based Load Balancer & Not Pushing ELI/EL 624 o The responder MUST set {L=0, E=0} in DS flags. 626 o If Multipath Information Type {2, 4, 8} is received, the responder 627 MUST comply with [RFC4379] and [RFC6424]. 629 o If Multipath Information Type {9} is received, the responder MUST 630 reply with Multipath Type {0}. 632 o If Multipath Information Type {TBD4} is received, the following 633 procedures are to be used: 635 * The responder MUST reply with Multipath Information Type 636 {TBD4}. 638 * The "Label Multipath Information" and "Associated Label 639 Multipath Information" sections MUST be omitted (NULL). 641 * If no matching IP address is found, then the "IPMultipathType" 642 field MUST be set to Multipath Information Type {0} and the "IP 643 Multipath Information" section MUST also be omitted (NULL). 645 * If at least one matching IP address is found, then the 646 "IPMultipathType" field MUST be set to appropriate Multipath 647 Information Type {2, 4, 8} and the "IP Multipath Information" 648 section MUST be included. 650 9.2. IP Based Load Balancer & Pushes ELI/EL 652 o The responder MUST set {L=0, E=1} in DS flags. 654 o If Multipath Information Type {9} is received, the responder MUST 655 reply with Multipath Type {0}. 657 o If Multipath Type {2, 4, 8, TBD4} is received, the following 658 procedures are to be used: 660 * The responder MUST respond with Multipath Type {TBD4}. See 661 Section 7 for details of Multipath Type {TBD4}. 663 * The "Label Multipath Information" section MUST be omitted 664 (i.e., it is not there). 666 * The IP address set specified in the received IP Multipath 667 Information MUST be used to determine the returned IP/Label 668 pairs. 670 * If the received Multipath Information Type was {TBD4}, the 671 received "Label Multipath Information" sections MUST NOT be 672 used to determine the associated label portion of the returned 673 IP/Label pairs. 675 * If no matching IP address is found, then the "IPMultipathType" 676 field MUST be set to Multipath Information Type {0} and the "IP 677 Multipath Information" section MUST be omitted. In addition, 678 the "Assoc Label Multipath Length" MUST be set to 0, and the 679 "Associated Label Multipath Information" section MUST also be 680 omitted. 682 * If at least one matching IP address is found, then the 683 "IPMultipathType" field MUST be set to appropriate Multipath 684 Information Type {2, 4, 8} and the "IP Multipath Information" 685 section MUST be included. In addition, the "Associated Label 686 Multipath Information" section MUST be populated with a list of 687 labels corresponding to each IP address specified in the "IP 688 Multipath Information" section. "Assoc Label Multipath Length" 689 MUST be set to a value representing the length in octets of the 690 "Associated Label Multipath Information" field. 692 9.3. Label-based Load Balancer & Not Pushing ELI/EL 694 o The responder MUST set {L=1, E=0} in DS flags. 696 o If Multipath Information Type {2, 4, 8} is received, the responder 697 MUST reply with Multipath Type {0}. 699 o If Multipath Information Type {9} is received, the responder MUST 700 comply with [RFC4379] and [RFC6424] as updated by Section 3. 702 o If Multipath Information Type {TBD4} is received, the following 703 procedures are to be used: 705 * The responder MUST reply with Multipath Information Type 706 {TBD4}. 708 * The "IP Multipath Information" and "Associated Label Multipath 709 Information" sections MUST be omitted (NULL). 711 * If no matching label is found, then the "LbMultipathType" field 712 MUST be set to Multipath Information Type {0} and the "Label 713 Multipath Information" section MUST also be omitted (NULL). 715 * If at least one matching label is found, then the 716 "LbMultipathType" field MUST be set to the appropriate 717 Multipath Information Type {9} and the "Label Multipath 718 Information" section MUST be included. 720 9.4. Label-based Load Balancer & Pushes ELI/EL 722 o The responder MUST set {L=1, E=1} in DS flags. 724 o If Multipath Information Type {2, 4, 8} is received, the responder 725 MUST reply with Multipath Type {0}. 727 o If Multipath Type {9, TBD4} is received, the following procedures 728 are to be used: 730 * The responder MUST respond with Multipath Type {TBD4}. 732 * The "IP Multipath Information" section MUST be omitted. 734 * The label set specified in the received Label Multipath 735 Information MUST be used to determine the returned Label/Label 736 pairs. 738 * If received Multipath Information Type was {TBD4}, received 739 "Label Multipath Information" sections MUST NOT be used to 740 determine the associated label portion of the returned Label/ 741 Label pairs. 743 * If no matching label is found, then the "LbMultipathType" field 744 MUST be set to Multipath Information Type {0} and "Label 745 Multipath Information" section MUST be omitted. In addition, 746 "Assoc Label Multipath Length" MUST be set to 0, and the 747 "Associated Label Multipath Information" section MUST also be 748 omitted. 750 * If at least one matching label is found, then the 751 "LbMultipathType" field MUST be set to the appropriate 752 Multipath Information Type {9} and the "Label Multipath 753 Information" section MUST be included. In addition, the 754 "Associated Label Multipath Information" section MUST be 755 populated with a list of labels corresponding to each label 756 specified in the "Label Multipath Information" section. "Assoc 757 Label Multipath Length" MUST be set to a value representing the 758 length in octets of the "Associated Label Multipath 759 Information" field. 761 9.5. Flow-Aware MS-PW Stitching LSR 763 A stitching LSR that cross-connects flow-aware Pseudowires behaves in 764 one of two ways: 766 o Load balances on the previous flow label, and carries over the 767 same flow label. For this case, the stitching LSR is to behave as 768 described in Section 9.3. 770 o Load balances on the previous flow label, and replaces the flow 771 label with a newly computed label. For this case, the stitching 772 LSR is to behave as described in Section 9.4. 774 10. Supported and Unsupported Cases 776 The MPLS architecture does not define strict rules on how 777 implementations are to identify hash "keys" for load balancing 778 purposes. As a result, implementations may be of the following load 779 balancer types: 781 1. IP-based load balancer. 782 2. Label-based load balancer. 783 3. Label- and IP-based load balancer. 785 For cases (2) and (3), an implementation can include different sets 786 of labels from the label stack for load balancing purpose. Thus the 787 following sub-cases are possible: 789 a. Entire label stack. 790 b. Top N labels from label stack where the number of labels in label 791 stack is > N. 792 c. Bottom N labels from label stack where the number of labels in 793 label stack is > N. 795 In a scenario where there is one flow label or entropy label present 796 in the label stack, the following further cases are possible for 797 (2b), (2c), (3b) and (3c): 799 1. N labels from label stack include flow label or entropy label. 800 2. N labels from label stack do not include flow label or entropy 801 label. 803 Also in a scenario where there are multiple entropy labels present in 804 the label stack, it is possible for implementations to employ 805 deviating techniques: 807 o Search for entropy stops at the first entropy label. 809 o Search for entropy includes any entropy label found plus continues 810 to search for entropy in the label stack. 812 Furthermore, handling of reserved (i.e., special) labels varies among 813 implementations: 815 o Reserved labels are used in the hash as any other label would be 816 (not a recommended practice.) 817 o Reserved labels are skipped over and, for implementations limited 818 to N labels, the reserved labels do not count towards the limit of 819 N. 820 o Reserved labels are skipped over and, for implementations limited 821 to N labels, the reserved labels count towards the limit of N. 823 It is important to point this out since the presence of GAL will 824 affect those implementations which include reserved labels for load 825 balancing purposes. 827 As can be seen from the above, there are many types of potential load 828 balancing implementations. Attempting for any OAM tools to support 829 ECMP discovery and traversal over all types would require fairly 830 complex procedures. Complexities in OAM tools have minimal benefit 831 if the majority of implementations are expected to employ only a 832 small subset of the cases described above. 834 o Section 4.3 of [RFC6790] states that in implementations, for load 835 balancing purposes, parsing beyond the label stack after finding 836 an entropy label has "limited incremental value". Therefore, it 837 is expected that most implementations will be of types "IP-based 838 load balancer" or "Label-based load balancer". 840 o Section 2.4.5.1 of [RFC7325] recommends that searching for entropy 841 labels in the label stack should terminate upon finding the first 842 entropy label. Therefore, it is expected that implementations 843 will only include the first (top-most) entropy label when there 844 are multiple entropy labels in the label stack. 846 o It is expected that, in most cases, the number of labels in the 847 label stack will not exceed the number of labels (N) which 848 implementations can include for load balancing purposes. 850 o It is expected that labels in the label stack, besides the flow 851 label and entropy label, are constant for the lifetime of a single 852 LSP multipath traceroute operation. Therefore, deviating load 853 balancing implementations with respect to reserved labels should 854 not affect this tool. 856 Thus [RFC4379], [RFC6424], and this document support cases (1) and 857 (2a1), where only the first (top-most) entropy label is included when 858 there are multiple entropy labels in the label stack. 860 11. Security Considerations 862 While [RFC4379] and [RFC6424] already allow for the discovery and 863 exercise of ECMP paths, this document extends the LSP Ping and 864 Traceroute mechanisms to more precisely discover and exercise ECMP 865 paths when an LSP uses ELI/EL in the label stack. Sourcing or 866 inspecting LSP Ping packets can be used for network reconnaissance. 868 The extended capability defined in this document requires small 869 additional processing for the responder and initiator nodes. The 870 responder node that pushes ELI/EL will need to compute and return 871 multipath data including associated EL. The initiator node will need 872 to store and handle both IP Multipath and Label Multipath 873 Information, and include destination IP addresses and/or ELs in MPLS 874 echo request packets as well as in Multipath Information sent to 875 downstream nodes. The security considerations of [RFC4379] already 876 cover Denial-of-Service attacks by regulating LSP Ping traffic going 877 to the control plane. 879 Finally, the security measures described in [RFC4379], [RFC6424], and 880 [RFC6790] are applicable. [RFC6424] provides guidelines if a network 881 operator wants to prevent tracing or does not want to expose details 882 of the tunnel and [RFC6790] provides guidance on the use of the EL. 884 12. IANA Considerations 886 12.1. Entropy Label FEC 888 The IANA is requested to assign a new sub-TLV from the "Sub-TLVs for 889 TLV Types 1, 16, and 21" section from the "Multi-Protocol Label 890 Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" 891 registry ([IANA-MPLS-LSP-PING]). 893 Sub-Type Sub-TLV Name Reference 894 -------- ------------ --------- 895 TBD1 Entropy label FEC this document 897 12.2. DS Flags 899 The IANA is requested to assign new bit numbers from the "DS flags" 900 sub-registry from the "Multi-Protocol Label Switching (MPLS) Label 901 Switched Paths (LSPs) Ping Parameters - TLVs" registry 902 ([IANA-MPLS-LSP-PING]). 904 Note: the "DS flags" sub-registry is created by [RFC7537]. 906 Bit number Name Reference 907 ---------- ---------------------------------------- --------- 908 TBD2 E: ELI/EL push indicator this document 909 TBD3 L: Label-based load balance indicator this document 911 12.3. Multipath Type 913 The IANA is requested to assign a new value from the "Multipath Type" 914 sub-registry from the "Multi-Protocol Label Switching (MPLS) Label 915 Switched Paths (LSPs) Ping Parameters - TLVs" registry 916 ([IANA-MPLS-LSP-PING]). 918 Note: The "Multipath Type" sub-registry is created by [RFC7537]. 920 Value Meaning Reference 921 ---------- ---------------------------------------- --------- 922 TBD4 IP and label set this document 924 13. Acknowledgements 926 The authors would like to thank Loa Andersson, Curtis Villamizar, 927 Daniel King, Sriganesh Kini, Victor Ji, Acee Lindem, Deborah 928 Brungard, Shawn M Emery, Scott O. Bradner, and Peter Yee for 929 performing thorough reviews and providing most valuable comments. 931 Carlos Pignataro would like to acknowledge his lifetime friend Martin 932 Rigueiro, with deep gratutide and esteem, for sharing his contagious 933 passion for engineering and sciences, and for selflessly teaching so 934 many lessons. 936 14. Contributing Authors 938 Nagendra Kumar 939 Cisco Systems, Inc. 941 Email: naikumar@cisco.com 943 15. References 945 15.1. Normative References 947 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 948 Requirement Levels", BCP 14, RFC 2119, 949 DOI 10.17487/RFC2119, March 1997, 950 . 952 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 953 Label Switched (MPLS) Data Plane Failures", RFC 4379, 954 DOI 10.17487/RFC4379, February 2006, 955 . 957 [RFC6424] Bahadur, N., Kompella, K., and G. Swallow, "Mechanism for 958 Performing Label Switched Path Ping (LSP Ping) over MPLS 959 Tunnels", RFC 6424, DOI 10.17487/RFC6424, November 2011, 960 . 962 [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and 963 L. Yong, "The Use of Entropy Labels in MPLS Forwarding", 964 RFC 6790, DOI 10.17487/RFC6790, November 2012, 965 . 967 [RFC7537] Decraene, B., Akiya, N., Pignataro, C., Andersson, L., and 968 S. Aldrin, "IANA Registries for LSP Ping Code Points", 969 RFC 7537, DOI 10.17487/RFC7537, May 2015, 970 . 972 15.2. Informative References 974 [IANA-MPLS-LSP-PING] 975 IANA, "Multi-Protocol Label Switching (MPLS) Label 976 Switched Paths (LSPs) Ping Parameters", 977 . 980 [RFC6391] Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V., 981 Regan, J., and S. Amante, "Flow-Aware Transport of 982 Pseudowires over an MPLS Packet Switched Network", 983 RFC 6391, DOI 10.17487/RFC6391, November 2011, 984 . 986 [RFC7325] Villamizar, C., Ed., Kompella, K., Amante, S., Malis, A., 987 and C. Pignataro, "MPLS Forwarding Compliance and 988 Performance Requirements", RFC 7325, DOI 10.17487/RFC7325, 989 August 2014, . 991 Authors' Addresses 993 Nobo Akiya 994 Big Switch Networks 996 Email: nobo.akiya.dev@gmail.com 997 George Swallow 998 Cisco Systems, Inc. 1000 Email: swallow@cisco.com 1002 Carlos Pignataro 1003 Cisco Systems, Inc. 1005 Email: cpignata@cisco.com 1007 Andrew G. Malis 1008 Huawei Technologies 1010 Email: agmalis@gmail.com 1012 Sam Aldrin 1013 Google 1015 Email: aldrin.ietf@gmail.com