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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) == Missing Reference: 'FEC-stack-depth' is mentioned on line 1850, but not defined ** Downref: Normative reference to an Informational RFC: RFC 4026 ** Obsolete normative reference: RFC 4379 (Obsoleted by RFC 8029) ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) -- Obsolete informational reference (is this intentional?): RFC 3107 (Obsoleted by RFC 8277) -- Obsolete informational reference (is this intentional?): RFC 4447 (Obsoleted by RFC 8077) Summary: 4 errors (**), 0 flaws (~~), 5 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Pignataro 3 Internet-Draft N. Kumar 4 Obsoletes: 4379, 6829 (if approved) Cisco 5 Intended status: Standards Track S. Aldrin 6 Expires: April 13, 2016 Google 7 M. Chen 8 Huawei 9 October 11, 2015 11 Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures 12 draft-smack-mpls-rfc4379bis-07 14 Abstract 16 This document describes a simple and efficient mechanism that can be 17 used to detect data plane failures in Multi-Protocol Label Switching 18 (MPLS) Label Switched Paths (LSPs). There are two parts to this 19 document: information carried in an MPLS "echo request" and "echo 20 reply" for the purposes of fault detection and isolation, and 21 mechanisms for reliably sending the echo reply. 23 This document obsoletes RFC 4379. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on April 13, 2016. 42 Copyright Notice 44 Copyright (c) 2015 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 60 1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4 61 1.2. Structure of This Document . . . . . . . . . . . . . . . 4 62 1.3. Contributors . . . . . . . . . . . . . . . . . . . . . . 4 63 1.4. Scope of RFC4379bis work . . . . . . . . . . . . . . . . 5 64 1.5. ToDo . . . . . . . . . . . . . . . . . . . . . . . . . . 5 65 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 2.1. Use of Address Range 127/8 . . . . . . . . . . . . . . . 6 67 2.2. Router Alert Option . . . . . . . . . . . . . . . . . . . 8 68 3. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . 8 69 3.1. Return Codes . . . . . . . . . . . . . . . . . . . . . . 13 70 3.2. Target FEC Stack . . . . . . . . . . . . . . . . . . . . 13 71 3.2.1. LDP IPv4 Prefix . . . . . . . . . . . . . . . . . . . 15 72 3.2.2. LDP IPv6 Prefix . . . . . . . . . . . . . . . . . . . 15 73 3.2.3. RSVP IPv4 LSP . . . . . . . . . . . . . . . . . . . . 15 74 3.2.4. RSVP IPv6 LSP . . . . . . . . . . . . . . . . . . . . 16 75 3.2.5. VPN IPv4 Prefix . . . . . . . . . . . . . . . . . . . 16 76 3.2.6. VPN IPv6 Prefix . . . . . . . . . . . . . . . . . . . 17 77 3.2.7. L2 VPN Endpoint . . . . . . . . . . . . . . . . . . . 18 78 3.2.8. FEC 128 Pseudowire - IPv4 (Deprecated) . . . . . . . 18 79 3.2.9. FEC 128 Pseudowire - IPv4 (Current) . . . . . . . . . 19 80 3.2.10. FEC 129 Pseudowire - IPv4 . . . . . . . . . . . . . . 20 81 3.2.11. BGP Labeled IPv4 Prefix . . . . . . . . . . . . . . . 21 82 3.2.12. BGP Labeled IPv6 Prefix . . . . . . . . . . . . . . . 21 83 3.2.13. Generic IPv4 Prefix . . . . . . . . . . . . . . . . . 22 84 3.2.14. Generic IPv6 Prefix . . . . . . . . . . . . . . . . . 22 85 3.2.15. Nil FEC . . . . . . . . . . . . . . . . . . . . . . . 23 86 3.2.16. FEC 128 Pseudowire - IPv6 . . . . . . . . . . . . . . 23 87 3.2.17. FEC 129 Pseudowire - IPv6 . . . . . . . . . . . . . . 24 88 3.3. Downstream Mapping . . . . . . . . . . . . . . . . . . . 25 89 3.3.1. Multipath Information Encoding . . . . . . . . . . . 28 90 3.3.2. Downstream Router and Interface . . . . . . . . . . . 30 91 3.4. Pad TLV . . . . . . . . . . . . . . . . . . . . . . . . . 31 92 3.5. Vendor Enterprise Number . . . . . . . . . . . . . . . . 31 93 3.6. Interface and Label Stack . . . . . . . . . . . . . . . . 32 94 3.7. Errored TLVs . . . . . . . . . . . . . . . . . . . . . . 33 95 3.8. Reply TOS Byte TLV . . . . . . . . . . . . . . . . . . . 33 96 4. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 34 97 4.1. Dealing with Equal-Cost Multi-Path (ECMP) . . . . . . . . 34 98 4.2. Testing LSPs That Are Used to Carry MPLS Payloads . . . . 35 99 4.3. Sending an MPLS Echo Request . . . . . . . . . . . . . . 35 100 4.4. Receiving an MPLS Echo Request . . . . . . . . . . . . . 36 101 4.4.1. FEC Validation . . . . . . . . . . . . . . . . . . . 42 102 4.5. Sending an MPLS Echo Reply . . . . . . . . . . . . . . . 43 103 4.6. Receiving an MPLS Echo Reply . . . . . . . . . . . . . . 44 104 4.7. Issue with VPN IPv4 and IPv6 Prefixes . . . . . . . . . . 44 105 4.8. Non-compliant Routers . . . . . . . . . . . . . . . . . . 45 106 5. Security Considerations . . . . . . . . . . . . . . . . . . . 45 107 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46 108 6.1. Message Types, Reply Modes, Return Codes . . . . . . . . 47 109 6.2. TLVs . . . . . . . . . . . . . . . . . . . . . . . . . . 47 110 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 48 111 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 49 112 8.1. Normative References . . . . . . . . . . . . . . . . . . 49 113 8.2. Informative References . . . . . . . . . . . . . . . . . 50 114 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51 116 1. Introduction 118 This document describes a simple and efficient mechanism that can be 119 used to detect data plane failures in MPLS Label Switched Paths 120 (LSPs). There are two parts to this document: information carried in 121 an MPLS "echo request" and "echo reply", and mechanisms for 122 transporting the echo reply. The first part aims at providing enough 123 information to check correct operation of the data plane, as well as 124 a mechanism to verify the data plane against the control plane, and 125 thereby localize faults. The second part suggests two methods of 126 reliable reply channels for the echo request message for more robust 127 fault isolation. 129 An important consideration in this design is that MPLS echo requests 130 follow the same data path that normal MPLS packets would traverse. 131 MPLS echo requests are meant primarily to validate the data plane, 132 and secondarily to verify the data plane against the control plane. 133 Mechanisms to check the control plane are valuable, but are not 134 covered in this document. 136 This document makes special use of the address range 127/8. This is 137 an exception to the behavior defined in RFC 1122 [RFC1122] and 138 updates that RFC. The motivation for this change and the details of 139 this exceptional use are discussed in section 2.1 below. 141 1.1. Conventions 143 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 144 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 145 document are to be interpreted as described in RFC 2119 [RFC2119]. 147 The term "Must Be Zero" (MBZ) is used in object descriptions for 148 reserved fields. These fields MUST be set to zero when sent and 149 ignored on receipt. 151 Terminology pertaining to L2 and L3 Virtual Private Networks (VPNs) 152 is defined in [RFC4026]. 154 Since this document refers to the MPLS Time to Live (TTL) far more 155 frequently than the IP TTL, the authors have chosen the convention of 156 using the unqualified "TTL" to mean "MPLS TTL" and using "IP TTL" for 157 the TTL value in the IP header. 159 1.2. Structure of This Document 161 The body of this memo contains four main parts: motivation, MPLS echo 162 request/reply packet format, LSP ping operation, and a reliable 163 return path. It is suggested that first-time readers skip the actual 164 packet formats and read the Theory of Operation first; the document 165 is structured the way it is to avoid forward references. 167 1.3. Contributors 169 A mechanism used to detect data plane failures in Multi-Protocol 170 Label Switching (MPLS) Label Switched Paths (LSPs) was originally 171 published as RFC 4379 in February 2006. It was produced by the MPLS 172 Working Group of the IETF and was jointly authored by Kireeti 173 Kompella and George Swallow. 175 The following made vital contributions to all aspects of the original 176 RFC 4379, and much of the material came out of debate and discussion 177 among this group. 179 Ronald P. Bonica, Juniper Networks, Inc. 180 Dave Cooper, Global Crossing 181 Ping Pan, Hammerhead Systems 182 Nischal Sheth, Juniper Networks, Inc. 183 Sanjay Wadhwa, Juniper Networks, Inc. 185 1.4. Scope of RFC4379bis work 187 The goal of this document is to take LSP Ping to an Internet 188 Standard. 190 [RFC4379] defines the basic mechanism for MPLS LSP validation that 191 can be used for fault detection and isolation. The scope of this 192 document also is to address various updates to MPLS LSP Ping, 193 including: 195 1. Updates to all references and citations. Obsoleted RFCs 2434, 196 2030, and 3036 are respectively replaced with RFCs 5226, 5905, 197 and 5036. Additionally, these three documents published as RFCs: 198 RFCs 4447, 5085, and 4761. 199 2. Incorporate all outstanding Errata. These include Erratum with 200 IDs: 108, 1418, 1714, 1786, 3399, 742, and 2978. 201 3. Replace EXP with Traffic Class (TC), based on the update from RFC 202 5462. 203 4. Incorporate the updates from RFC 6829, adding the PW FECs 204 advertised over IPv6. 205 5. Incorporate the updates from RFC 7506, adding IPv6 Router Alert 206 Option for MPLS OAM. 208 1.5. ToDo 210 This section should be empty, and removed, prior to publication. 211 ToDos: 213 1. Evaluation of which of the RFCs that updated RFC 4379 need to be 214 incorporated into this 4379bis document. Specifically, these 215 RFCs updated RFC 4379: 6424, 6425, 6426 and 7537. RFCs that 216 updated RFC 4379 and are incorporated into this 4379bis, will be 217 Obsoleted by 4379bis. 218 2. Review IANA Allocations 220 2. Motivation 222 When an LSP fails to deliver user traffic, the failure cannot always 223 be detected by the MPLS control plane. There is a need to provide a 224 tool that would enable users to detect such traffic "black holes" or 225 misrouting within a reasonable period of time, and a mechanism to 226 isolate faults. 228 In this document, we describe a mechanism that accomplishes these 229 goals. This mechanism is modeled after the ping/traceroute paradigm: 230 ping (ICMP echo request [RFC0792]) is used for connectivity checks, 231 and traceroute is used for hop-by-hop fault localization as well as 232 path tracing. This document specifies a "ping" mode and a 233 "traceroute" mode for testing MPLS LSPs. 235 The basic idea is to verify that packets that belong to a particular 236 Forwarding Equivalence Class (FEC) actually end their MPLS path on a 237 Label Switching Router (LSR) that is an egress for that FEC. This 238 document proposes that this test be carried out by sending a packet 239 (called an "MPLS echo request") along the same data path as other 240 packets belonging to this FEC. An MPLS echo request also carries 241 information about the FEC whose MPLS path is being verified. This 242 echo request is forwarded just like any other packet belonging to 243 that FEC. In "ping" mode (basic connectivity check), the packet 244 should reach the end of the path, at which point it is sent to the 245 control plane of the egress LSR, which then verifies whether it is 246 indeed an egress for the FEC. In "traceroute" mode (fault 247 isolation), the packet is sent to the control plane of each transit 248 LSR, which performs various checks that it is indeed a transit LSR 249 for this path; this LSR also returns further information that helps 250 check the control plane against the data plane, i.e., that forwarding 251 matches what the routing protocols determined as the path. 253 One way these tools can be used is to periodically ping an FEC to 254 ensure connectivity. If the ping fails, one can then initiate a 255 traceroute to determine where the fault lies. One can also 256 periodically traceroute FECs to verify that forwarding matches the 257 control plane; however, this places a greater burden on transit LSRs 258 and thus should be used with caution. 260 2.1. Use of Address Range 127/8 262 As described above, LSP ping is intended as a diagnostic tool. It is 263 intended to enable providers of an MPLS-based service to isolate 264 network faults. In particular, LSP ping needs to diagnose situations 265 where the control and data planes are out of sync. It performs this 266 by routing an MPLS echo request packet based solely on its label 267 stack. That is, the IP destination address is never used in a 268 forwarding decision. In fact, the sender of an MPLS echo request 269 packet may not know, a priori, the address of the router at the end 270 of the LSP. 272 Providers of MPLS-based services also need the ability to trace all 273 of the possible paths that an LSP may take. Since most MPLS services 274 are based on IP unicast forwarding, these paths are subject to equal- 275 cost multi-path (ECMP) load sharing. 277 This leads to the following requirements: 279 1. Although the LSP in question may be broken in unknown ways, the 280 likelihood of a diagnostic packet being delivered to a user of an 281 MPLS service MUST be held to an absolute minimum. 283 2. If an LSP is broken in such a way that it prematurely terminates, 284 the diagnostic packet MUST NOT be IP forwarded. 286 3. A means of varying the diagnostic packets such that they exercise 287 all ECMP paths is thus REQUIRED. 289 Clearly, using general unicast addresses satisfies neither of the 290 first two requirements. A number of other options for addresses were 291 considered, including a portion of the private address space (as 292 determined by the network operator) and the newly designated IPv4 293 link local addresses. Use of the private address space was deemed 294 ineffective since the leading MPLS-based service is an IPv4 Virtual 295 Private Network (VPN). VPNs often use private addresses. 297 The IPv4 link local addresses are more attractive in that the scope 298 over which they can be forwarded is limited. However, if one were to 299 use an address from this range, it would still be possible for the 300 first recipient of a diagnostic packet that "escaped" from a broken 301 LSP to have that address assigned to the interface on which it 302 arrived and thus could mistakenly receive such a packet. 303 Furthermore, the IPv4 link local address range has only recently been 304 allocated. Many deployed routers would forward a packet with an 305 address from that range toward the default route. 307 The 127/8 range for IPv4 and that same range embedded in as 308 IPv4-mapped IPv6 addresses for IPv6 was chosen for a number of 309 reasons. 311 RFC 1122 allocates the 127/8 as "Internal host loopback address" and 312 states: "Addresses of this form MUST NOT appear outside a host." 313 Thus, the default behavior of hosts is to discard such packets. This 314 helps to ensure that if a diagnostic packet is misdirected to a host, 315 it will be silently discarded. 317 RFC 1812 [RFC1812] states: 319 A router SHOULD NOT forward, except over a loopback interface, any 320 packet that has a destination address on network 127. A router 321 MAY have a switch that allows the network manager to disable these 322 checks. If such a switch is provided, it MUST default to 323 performing the checks. 325 This helps to ensure that diagnostic packets are never IP forwarded. 327 The 127/8 address range provides 16M addresses allowing wide 328 flexibility in varying addresses to exercise ECMP paths. Finally, as 329 an implementation optimization, the 127/8 provides an easy means of 330 identifying possible LSP packets. 332 2.2. Router Alert Option 334 This document requires the use of the Router Alert Option (RAO) set 335 in IP header in order to have the transit node process the MPLS OAM 336 payload. 338 [RFC2113] defines a generic Option Value 0x0 for IPv4 RAO that alerts 339 transit router to examine the IPv4 packet. [RFC7506] defines MPLS 340 OAM Option Value 69 for IPv6 RAO to alert transit routers to examine 341 the IPv6 packet more closely for MPLS OAM purposes. 343 The use of the Router Alert IP Option in this document is as follows: 345 In case of an IPv4 header, the generic IPv4 RAO value 0x0 346 [RFC2113] SHOULD be used. In case of an IPv6 header, the IPv6 RAO 347 value (69) for MPLS OAM [RFC7506] MUST be used. 349 3. Packet Format 351 An MPLS echo request is a (possibly labeled) IPv4 or IPv6 UDP packet; 352 the contents of the UDP packet have the following format: 354 0 1 2 3 355 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 1 356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 357 | Version Number | Global Flags | 358 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 359 | Message Type | Reply mode | Return Code | Return Subcode| 360 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 361 | Sender's Handle | 362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 363 | Sequence Number | 364 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 365 | TimeStamp Sent (seconds) | 366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 367 | TimeStamp Sent (seconds fraction) | 368 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 369 | TimeStamp Received (seconds) | 370 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 371 | TimeStamp Received (seconds fraction) | 372 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 373 | TLVs ... | 374 . . 375 . . 376 . . 377 | | 378 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 380 The Version Number is currently 1. (Note: the version number is to 381 be incremented whenever a change is made that affects the ability of 382 an implementation to correctly parse or process an MPLS echo request/ 383 reply. These changes include any syntactic or semantic changes made 384 to any of the fixed fields, or to any Type-Length-Value (TLV) or sub- 385 TLV assignment or format that is defined at a certain version number. 386 The version number may not need to be changed if an optional TLV or 387 sub-TLV is added.) 389 The Global Flags field is a bit vector with the following format: 391 0 1 392 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 393 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 394 | MBZ |V| 395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 397 One flag is defined for now, the V bit; the rest MUST be set to zero 398 when sending and ignored on receipt. 400 The V (Validate FEC Stack) flag is set to 1 if the sender wants the 401 receiver to perform FEC Stack validation; if V is 0, the choice is 402 left to the receiver. 404 The Message Type is one of the following: 406 Value Meaning 407 ----- ------- 408 1 MPLS echo request 409 2 MPLS echo reply 411 The Reply Mode can take one of the following values: 413 Value Meaning 414 ----- ------- 415 1 Do not reply 416 2 Reply via an IPv4/IPv6 UDP packet 417 3 Reply via an IPv4/IPv6 UDP packet with Router Alert 418 4 Reply via application level control channel 420 An MPLS echo request with 1 (Do not reply) in the Reply Mode field 421 may be used for one-way connectivity tests; the receiving router may 422 log gaps in the Sequence Numbers and/or maintain delay/jitter 423 statistics. An MPLS echo request would normally have 2 (Reply via an 424 IPv4/IPv6 UDP packet) in the Reply Mode field. If the normal IP 425 return path is deemed unreliable, one may use 3 (Reply via an IPv4/ 426 IPv6 UDP packet with Router Alert). Note that this requires that all 427 intermediate routers understand and know how to forward MPLS echo 428 replies. The echo reply uses the same IP version number as the 429 received echo request, i.e., an IPv4 encapsulated echo reply is sent 430 in response to an IPv4 encapsulated echo request. 432 Some applications support an IP control channel. One such example is 433 the associated control channel defined in Virtual Circuit 434 Connectivity Verification (VCCV) [RFC5085]. Any application that 435 supports an IP control channel between its control entities may set 436 the Reply Mode to 4 (Reply via application level control channel) to 437 ensure that replies use that same channel. Further definition of 438 this codepoint is application specific and thus beyond the scope of 439 this document. 441 Return Codes and Subcodes are described in the next section. 443 The Sender's Handle is filled in by the sender, and returned 444 unchanged by the receiver in the echo reply (if any). There are no 445 semantics associated with this handle, although a sender may find 446 this useful for matching up requests with replies. 448 The Sequence Number is assigned by the sender of the MPLS echo 449 request and can be (for example) used to detect missed replies. 451 The TimeStamp Sent is the time-of-day (according to the sender's 452 clock) in NTP format [RFC5905] when the MPLS echo request is sent. 453 The TimeStamp Received in an echo reply is the time-of-day (according 454 to the receiver's clock) in NTP format that the corresponding echo 455 request was received. 457 TLVs (Type-Length-Value tuples) have the following format: 459 0 1 2 3 460 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 1 461 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 462 | Type | Length | 463 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 464 | Value | 465 . . 466 . . 467 . . 468 | | 469 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 471 Types are defined below; Length is the length of the Value field in 472 octets. The Value field depends on the Type; it is zero padded to 473 align to a 4-octet boundary. TLVs may be nested within other TLVs, 474 in which case the nested TLVs are called sub-TLVs. Sub-TLVs have 475 independent types and MUST also be 4-octet aligned. 477 Two examples follow. The Label Distribution Protocol (LDP) IPv4 FEC 478 sub-TLV has the following format: 480 0 1 2 3 481 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 1 482 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 483 | Type = 1 (LDP IPv4 FEC) | Length = 5 | 484 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 485 | IPv4 prefix | 486 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 487 | Prefix Length | Must Be Zero | 488 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 490 The Length for this TLV is 5. A Target FEC Stack TLV that contains 491 an LDP IPv4 FEC sub-TLV and a VPN IPv4 prefix sub-TLV has the 492 following format: 494 0 1 2 3 495 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 1 496 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 497 | Type = 1 (FEC TLV) | Length = 32 | 498 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 499 | sub-Type = 1 (LDP IPv4 FEC) | Length = 5 | 500 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 501 | IPv4 prefix | 502 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 503 | Prefix Length | Must Be Zero | 504 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 505 | sub-Type = 6 (VPN IPv4 prefix)| Length = 13 | 506 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 507 | Route Distinguisher | 508 | (8 octets) | 509 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 510 | IPv4 prefix | 511 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 512 | Prefix Length | Must Be Zero | 513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 515 A description of the Types and Values of the top-level TLVs for LSP 516 ping are given below: 518 Type # Value Field 519 ------ ----------- 520 1 Target FEC Stack 521 2 Downstream Mapping 522 3 Pad 523 4 Not Assigned 524 5 Vendor Enterprise Number 525 6 Not Assigned 526 7 Interface and Label Stack 527 8 Not Assigned 528 9 Errored TLVs 529 10 Reply TOS Byte 531 Types less than 32768 (i.e., with the high-order bit equal to 0) are 532 mandatory TLVs that MUST either be supported by an implementation or 533 result in the return code of 2 ("One or more of the TLVs was not 534 understood") being sent in the echo response. 536 Types greater than or equal to 32768 (i.e., with the high-order bit 537 equal to 1) are optional TLVs that SHOULD be ignored if the 538 implementation does not understand or support them. 540 3.1. Return Codes 542 The Return Code is set to zero by the sender. The receiver can set 543 it to one of the values listed below. The notation refers to 544 the Return Subcode. This field is filled in with the stack-depth for 545 those codes that specify that. For all other codes, the Return 546 Subcode MUST be set to zero. 548 Value Meaning 549 ----- ------- 550 0 No return code 551 1 Malformed echo request received 552 2 One or more of the TLVs was not understood 553 3 Replying router is an egress for the FEC at stack- 554 depth 555 4 Replying router has no mapping for the FEC at stack- 556 depth 557 5 Downstream Mapping Mismatch (See Note 1) 558 6 Upstream Interface Index Unknown (See Note 1) 559 7 Reserved 560 8 Label switched at stack-depth 561 9 Label switched but no MPLS forwarding at stack-depth 562 563 10 Mapping for this FEC is not the given label at stack- 564 depth 565 11 No label entry at stack-depth 566 12 Protocol not associated with interface at FEC stack- 567 depth 568 13 Premature termination of ping due to label stack 569 shrinking to a single label 571 Note 1 573 The Return Subcode contains the point in the label stack where 574 processing was terminated. If the RSC is 0, no labels were 575 processed. Otherwise the packet would have been label switched at 576 depth RSC. 578 3.2. Target FEC Stack 580 A Target FEC Stack is a list of sub-TLVs. The number of elements is 581 determined by looking at the sub-TLV length fields. 583 Sub-Type Length Value Field 584 -------- ------ ----------- 585 1 5 LDP IPv4 prefix 586 2 17 LDP IPv6 prefix 587 3 20 RSVP IPv4 LSP 588 4 56 RSVP IPv6 LSP 589 5 Not Assigned 590 6 13 VPN IPv4 prefix 591 7 25 VPN IPv6 prefix 592 8 14 L2 VPN endpoint 593 9 10 "FEC 128" Pseudowire - IPv4 (deprecated) 594 10 14 "FEC 128" Pseudowire - IPv4 595 11 16+ "FEC 129" Pseudowire - IPv4 596 12 5 BGP labeled IPv4 prefix 597 13 17 BGP labeled IPv6 prefix 598 14 5 Generic IPv4 prefix 599 15 17 Generic IPv6 prefix 600 16 4 Nil FEC 601 24 38 "FEC 128" Pseudowire - IPv6 602 25 40+ "FEC 129" Pseudowire - IPv6 604 Other FEC Types will be defined as needed. 606 Note that this TLV defines a stack of FECs, the first FEC element 607 corresponding to the top of the label stack, etc. 609 An MPLS echo request MUST have a Target FEC Stack that describes the 610 FEC Stack being tested. For example, if an LSR X has an LDP mapping 611 [RFC5036] for 192.168.1.1 (say, label 1001), then to verify that 612 label 1001 does indeed reach an egress LSR that announced this prefix 613 via LDP, X can send an MPLS echo request with an FEC Stack TLV with 614 one FEC in it, namely, of type LDP IPv4 prefix, with prefix 615 192.168.1.1/32, and send the echo request with a label of 1001. 617 Say LSR X wanted to verify that a label stack of <1001, 23456> is the 618 right label stack to use to reach a VPN IPv4 prefix [see section 619 3.2.5] of 10/8 in VPN foo. Say further that LSR Y with loopback 620 address 192.168.1.1 announced prefix 10/8 with Route Distinguisher 621 RD-foo-Y (which may in general be different from the Route 622 Distinguisher that LSR X uses in its own advertisements for VPN foo), 623 label 23456 and BGP next hop 192.168.1.1 [RFC4271]. Finally, suppose 624 that LSR X receives a label binding of 1001 for 192.168.1.1 via LDP. 625 X has two choices in sending an MPLS echo request: X can send an MPLS 626 echo request with an FEC Stack TLV with a single FEC of type VPN IPv4 627 prefix with a prefix of 10/8 and a Route Distinguisher of RD-foo-Y. 628 Alternatively, X can send an FEC Stack TLV with two FECs, the first 629 of type LDP IPv4 with a prefix of 192.168.1.1/32 and the second of 630 type of IP VPN with a prefix 10/8 with Route Distinguisher of RD-foo- 631 Y. In either case, the MPLS echo request would have a label stack of 632 <1001, 23456>. (Note: in this example, 1001 is the "outer" label and 633 23456 is the "inner" label.) 635 3.2.1. LDP IPv4 Prefix 637 The IPv4 Prefix FEC is defined in [RFC5036]. When an LDP IPv4 prefix 638 is encoded in a label stack, the following format is used. The value 639 consists of 4 octets of an IPv4 prefix followed by 1 octet of prefix 640 length in bits; the format is given below. The IPv4 prefix is in 641 network byte order; if the prefix is shorter than 32 bits, trailing 642 bits SHOULD be set to zero. See [RFC5036] for an example of a 643 Mapping for an IPv4 FEC. 645 0 1 2 3 646 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 1 647 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 648 | IPv4 prefix | 649 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 650 | Prefix Length | Must Be Zero | 651 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 653 3.2.2. LDP IPv6 Prefix 655 The IPv6 Prefix FEC is defined in [RFC5036]. When an LDP IPv6 prefix 656 is encoded in a label stack, the following format is used. The value 657 consists of 16 octets of an IPv6 prefix followed by 1 octet of prefix 658 length in bits; the format is given below. The IPv6 prefix is in 659 network byte order; if the prefix is shorter than 128 bits, the 660 trailing bits SHOULD be set to zero. See [RFC5036] for an example of 661 a Mapping for an IPv6 FEC. 663 0 1 2 3 664 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 1 665 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 666 | IPv6 prefix | 667 | (16 octets) | 668 | | 669 | | 670 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 671 | Prefix Length | Must Be Zero | 672 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 674 3.2.3. RSVP IPv4 LSP 676 The value has the format below. The value fields are taken from RFC 677 3209, sections 4.6.1.1 and 4.6.2.1. See [RFC3209]. 679 0 1 2 3 680 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 1 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 682 | IPv4 tunnel end point address | 683 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 684 | Must Be Zero | Tunnel ID | 685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 686 | Extended Tunnel ID | 687 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 688 | IPv4 tunnel sender address | 689 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 690 | Must Be Zero | LSP ID | 691 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 693 3.2.4. RSVP IPv6 LSP 695 The value has the format below. The value fields are taken from RFC 696 3209, sections 4.6.1.2 and 4.6.2.2. See [RFC3209]. 698 0 1 2 3 699 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 1 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 | IPv6 tunnel end point address | 702 | | 703 | | 704 | | 705 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 706 | Must Be Zero | Tunnel ID | 707 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 708 | Extended Tunnel ID | 709 | | 710 | | 711 | | 712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 713 | IPv6 tunnel sender address | 714 | | 715 | | 716 | | 717 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 718 | Must Be Zero | LSP ID | 719 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 721 3.2.5. VPN IPv4 Prefix 723 VPN-IPv4 Network Layer Routing Information (NLRI) is defined in 724 [RFC4365]. This document uses the term VPN IPv4 prefix for a VPN- 725 IPv4 NLRI that has been advertised with an MPLS label in BGP. See 726 [RFC3107]. 728 When a VPN IPv4 prefix is encoded in a label stack, the following 729 format is used. The value field consists of the Route Distinguisher 730 advertised with the VPN IPv4 prefix, the IPv4 prefix (with trailing 0 731 bits to make 32 bits in all), and a prefix length, as follows: 733 0 1 2 3 734 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 1 735 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 736 | Route Distinguisher | 737 | (8 octets) | 738 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 739 | IPv4 prefix | 740 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 741 | Prefix Length | Must Be Zero | 742 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 744 The Route Distinguisher (RD) is an 8-octet identifier; it does not 745 contain any inherent information. The purpose of the RD is solely to 746 allow one to create distinct routes to a common IPv4 address prefix. 747 The encoding of the RD is not important here. When matching this 748 field to the local FEC information, it is treated as an opaque value. 750 3.2.6. VPN IPv6 Prefix 752 VPN-IPv6 Network Layer Routing Information (NLRI) is defined in 753 [RFC4365]. This document uses the term VPN IPv6 prefix for a VPN- 754 IPv6 NLRI that has been advertised with an MPLS label in BGP. See 755 [RFC3107]. 757 When a VPN IPv6 prefix is encoded in a label stack, the following 758 format is used. The value field consists of the Route Distinguisher 759 advertised with the VPN IPv6 prefix, the IPv6 prefix (with trailing 0 760 bits to make 128 bits in all), and a prefix length, as follows: 762 0 1 2 3 763 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 1 764 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 765 | Route Distinguisher | 766 | (8 octets) | 767 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 768 | IPv6 prefix | 769 | | 770 | | 771 | | 772 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 773 | Prefix Length | Must Be Zero | 774 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 776 The Route Distinguisher is identical to the VPN IPv4 Prefix RD, 777 except that it functions here to allow the creation of distinct 778 routes to IPv6 prefixes. See section 3.2.5. When matching this 779 field to local FEC information, it is treated as an opaque value. 781 3.2.7. L2 VPN Endpoint 783 VPLS stands for Virtual Private LAN Service. The terms VPLS BGP NLRI 784 and VE ID (VPLS Edge Identifier) are defined in [RFC4761]. This 785 document uses the simpler term L2 VPN endpoint when referring to a 786 VPLS BGP NLRI. The Route Distinguisher is an 8-octet identifier used 787 to distinguish information about various L2 VPNs advertised by a 788 node. The VE ID is a 2-octet identifier used to identify a 789 particular node that serves as the service attachment point within a 790 VPLS. The structure of these two identifiers is unimportant here; 791 when matching these fields to local FEC information, they are treated 792 as opaque values. The encapsulation type is identical to the PW Type 793 in section 3.2.8 below. 795 When an L2 VPN endpoint is encoded in a label stack, the following 796 format is used. The value field consists of a Route Distinguisher (8 797 octets), the sender (of the ping)'s VE ID (2 octets), the receiver's 798 VE ID (2 octets), and an encapsulation type (2 octets), formatted as 799 follows: 801 0 1 2 3 802 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 1 803 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 804 | Route Distinguisher | 805 | (8 octets) | 806 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 807 | Sender's VE ID | Receiver's VE ID | 808 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 809 | Encapsulation Type | Must Be Zero | 810 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 812 3.2.8. FEC 128 Pseudowire - IPv4 (Deprecated) 814 FEC 128 (0x80) is defined in [RFC4447], as are the terms PW ID 815 (Pseudowire ID) and PW Type (Pseudowire Type). A PW ID is a non-zero 816 32-bit connection ID. The PW Type is a 15-bit number indicating the 817 encapsulation type. It is carried right justified in the field below 818 termed encapsulation type with the high-order bit set to zero. Both 819 of these fields are treated in this protocol as opaque values. 821 When an FEC 128 is encoded in a label stack, the following format is 822 used. The value field consists of the remote PE IPv4 address (the 823 destination address of the targeted LDP session), the PW ID, and the 824 encapsulation type as follows: 826 0 1 2 3 827 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 1 828 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 829 | Remote PE IPv4 Address | 830 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 831 | PW ID | 832 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 833 | PW Type | Must Be Zero | 834 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 836 This FEC is deprecated and is retained only for backward 837 compatibility. Implementations of LSP ping SHOULD accept and process 838 this TLV, but SHOULD send LSP ping echo requests with the new TLV 839 (see next section), unless explicitly configured to use the old TLV. 841 An LSR receiving this TLV SHOULD use the source IP address of the LSP 842 echo request to infer the sender's PE address. 844 3.2.9. FEC 128 Pseudowire - IPv4 (Current) 846 FEC 128 (0x80) is defined in [RFC4447], as are the terms PW ID 847 (Pseudowire ID) and PW Type (Pseudowire Type). A PW ID is a non-zero 848 32-bit connection ID. The PW Type is a 15-bit number indicating the 849 encapsulation type. It is carried right justified in the field below 850 termed encapsulation type with the high-order bit set to zero. 852 Both of these fields are treated in this protocol as opaque values. 853 When matching these field to the local FEC information, the match 854 MUST be exact. 856 When an FEC 128 is encoded in a label stack, the following format is 857 used. The value field consists of the sender's PE IPv4 address (the 858 source address of the targeted LDP session), the remote PE IPv4 859 address (the destination address of the targeted LDP session), the PW 860 ID, and the encapsulation type as follows: 862 0 1 2 3 863 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 1 864 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 865 | Sender's PE IPv4 Address | 866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 867 | Remote PE IPv4 Address | 868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 869 | PW ID | 870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 871 | PW Type | Must Be Zero | 872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 874 3.2.10. FEC 129 Pseudowire - IPv4 876 FEC 129 (0x81) and the terms PW Type, Attachment Group Identifier 877 (AGI), Attachment Group Identifier Type (AGI Type), Attachment 878 Individual Identifier Type (AII Type), Source Attachment Individual 879 Identifier (SAII), and Target Attachment Individual Identifier (TAII) 880 are defined in [RFC4447]. The PW Type is a 15-bit number indicating 881 the encapsulation type. It is carried right justified in the field 882 below PW Type with the high-order bit set to zero. All the other 883 fields are treated as opaque values and copied directly from the FEC 884 129 format. All of these values together uniquely define the FEC 885 within the scope of the LDP session identified by the source and 886 remote PE IPv4 addresses. 888 When an FEC 129 is encoded in a label stack, the following format is 889 used. The Length of this TLV is 16 + AGI length + SAII length + TAII 890 length. Padding is used to make the total length a multiple of 4; 891 the length of the padding is not included in the Length field. 893 0 1 2 3 894 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 1 895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 896 | Sender's PE IPv4 Address | 897 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 898 | Remote PE IPv4 Address | 899 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 900 | PW Type | AGI Type | AGI Length | 901 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 902 ~ AGI Value ~ 903 | | 904 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 905 | AII Type | SAII Length | SAII Value | 906 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 907 ~ SAII Value (continued) ~ 908 | | 909 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 910 | AII Type | TAII Length | TAII Value | 911 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 912 ~ TAII Value (continued) ~ 913 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 914 | TAII (cont.) | 0-3 octets of zero padding | 915 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 917 3.2.11. BGP Labeled IPv4 Prefix 919 BGP labeled IPv4 prefixes are defined in [RFC3107]. When a BGP 920 labeled IPv4 prefix is encoded in a label stack, the following format 921 is used. The value field consists the IPv4 prefix (with trailing 0 922 bits to make 32 bits in all), and the prefix length, as follows: 924 0 1 2 3 925 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 1 926 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 927 | IPv4 Prefix | 928 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 929 | Prefix Length | Must Be Zero | 930 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 932 3.2.12. BGP Labeled IPv6 Prefix 934 BGP labeled IPv6 prefixes are defined in [RFC3107]. When a BGP 935 labeled IPv6 prefix is encoded in a label stack, the following format 936 is used. The value consists of 16 octets of an IPv6 prefix followed 937 by 1 octet of prefix length in bits; the format is given below. The 938 IPv6 prefix is in network byte order; if the prefix is shorter than 939 128 bits, the trailing bits SHOULD be set to zero. 941 0 1 2 3 942 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 1 943 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 944 | IPv6 prefix | 945 | (16 octets) | 946 | | 947 | | 948 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 949 | Prefix Length | Must Be Zero | 950 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 952 3.2.13. Generic IPv4 Prefix 954 The value consists of 4 octets of an IPv4 prefix followed by 1 octet 955 of prefix length in bits; the format is given below. The IPv4 prefix 956 is in network byte order; if the prefix is shorter than 32 bits, 957 trailing bits SHOULD be set to zero. This FEC is used if the 958 protocol advertising the label is unknown or may change during the 959 course of the LSP. An example is an inter-AS LSP that may be 960 signaled by LDP in one Autonomous System (AS), by RSVP-TE [RFC3209] 961 in another AS, and by BGP between the ASes, such as is common for 962 inter-AS VPNs. 964 0 1 2 3 965 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 1 966 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 967 | IPv4 prefix | 968 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 969 | Prefix Length | Must Be Zero | 970 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 972 3.2.14. Generic IPv6 Prefix 974 The value consists of 16 octets of an IPv6 prefix followed by 1 octet 975 of prefix length in bits; the format is given below. The IPv6 prefix 976 is in network byte order; if the prefix is shorter than 128 bits, the 977 trailing bits SHOULD be set to zero. 979 0 1 2 3 980 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 1 981 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 982 | IPv6 prefix | 983 | (16 octets) | 984 | | 985 | | 986 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 987 | Prefix Length | Must Be Zero | 988 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 990 3.2.15. Nil FEC 992 At times, labels from the reserved range, e.g., Router Alert and 993 Explicit-null, may be added to the label stack for various diagnostic 994 purposes such as influencing load-balancing. These labels may have 995 no explicit FEC associated with them. The Nil FEC Stack is defined 996 to allow a Target FEC Stack sub-TLV to be added to the Target FEC 997 Stack to account for such labels so that proper validation can still 998 be performed. 1000 The Length is 4. Labels are 20-bit values treated as numbers. 1002 0 1 2 3 1003 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 1004 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1005 | Label | MBZ | 1006 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1008 Label is the actual label value inserted in the label stack; the MBZ 1009 fields MUST be zero when sent and ignored on receipt. 1011 3.2.16. FEC 128 Pseudowire - IPv6 1013 The FEC 128 Pseudowire IPv6 sub-TLV has a structure consistent with 1014 the FEC 128 Pseudowire IPv4 sub-TLV as described in Section 3.2.9. 1015 The value field consists of the Sender's PE IPv6 address (the source 1016 address of the targeted LDP session), the remote PE IPv6 address (the 1017 destination address of the targeted LDP session), the PW ID, and the 1018 encapsulation type as follows: 1020 0 1 2 3 1021 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 1022 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1023 ~ Sender's PE IPv6 Address ~ 1024 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1025 ~ Remote PE IPv6 Address ~ 1026 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1027 | PW ID | 1028 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1029 | PW Type | Must Be Zero | 1030 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1032 Sender's PE IPv6 Address: The source IP address of the target IPv6 1033 LDP session. 16 octets. 1035 Remote PE IPv6 Address: The destination IP address of the target IPv6 1036 LDP session. 16 octets. 1038 PW ID: Same as FEC 128 Pseudowire IPv4 in Section 3.2.9. 1040 PW Type: Same as FEC 128 Pseudowire IPv4 in Section 3.2.9. 1042 3.2.17. FEC 129 Pseudowire - IPv6 1044 The FEC 129 Pseudowire IPv6 sub-TLV has a structure consistent with 1045 the FEC 129 Pseudowire IPv4 sub-TLV as described in Section 3.2.10. 1046 When an FEC 129 is encoded in a label stack, the following format is 1047 used. The length of this TLV is 40 + AGI (Attachment Group 1048 Identifier) length + SAII (Source Attachment Individual Identifier) 1049 length + TAII (Target Attachment Individual Identifier) length. 1050 Padding is used to make the total length a multiple of 4; the length 1051 of the padding is not included in the Length field. 1053 0 1 2 3 1054 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 1055 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1056 ~ Sender's PE IPv6 Address ~ 1057 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1058 ~ Remote PE IPv6 Address ~ 1059 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1060 | PW Type | AGI Type | AGI Length | 1061 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1062 ~ AGI Value ~ 1063 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1064 | AII Type | SAII Length | SAII Value | 1065 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1066 ~ SAII Value (continued) ~ 1067 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1068 | AII Type | TAII Length | TAII Value | 1069 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1070 ~ TAII Value (continued) ~ 1071 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1072 | TAII (cont.) | 0-3 octets of zero padding | 1073 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1075 Sender's PE IPv6 Address: The source IP address of the target IPv6 1076 LDP session. 16 octets. 1078 Remote PE IPv6 Address: The destination IP address of the target IPv6 1079 LDP session. 16 octets. 1081 The other fields are the same as FEC 129 Pseudowire IPv4 in 1082 Section 3.2.10. 1084 3.3. Downstream Mapping 1086 The Downstream Mapping object is a TLV that MAY be included in an 1087 echo request message. Only one Downstream Mapping object may appear 1088 in an echo request. The presence of a Downstream Mapping object is a 1089 request that Downstream Mapping objects be included in the echo 1090 reply. If the replying router is the destination of the FEC, then a 1091 Downstream Mapping TLV SHOULD NOT be included in the echo reply. 1092 Otherwise the replying router SHOULD include a Downstream Mapping 1093 object for each interface over which this FEC could be forwarded. 1094 For a more precise definition of the notion of "downstream", see 1095 section 3.3.2, "Downstream Router and Interface". 1097 The Length is K + M + 4*N octets, where M is the Multipath Length, 1098 and N is the number of Downstream Labels. Values for K are found in 1099 the description of Address Type below. The Value field of a 1100 Downstream Mapping has the following format: 1102 0 1 2 3 1103 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 1104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1105 | MTU | Address Type | DS Flags | 1106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1107 | Downstream IP Address (4 or 16 octets) | 1108 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1109 | Downstream Interface Address (4 or 16 octets) | 1110 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1111 | Multipath Type| Depth Limit | Multipath Length | 1112 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1113 . . 1114 . (Multipath Information) . 1115 . . 1116 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1117 | Downstream Label | Protocol | 1118 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1119 . . 1120 . . 1121 . . 1122 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1123 | Downstream Label | Protocol | 1124 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1126 Maximum Transmission Unit (MTU) 1128 The MTU is the size in octets of the largest MPLS frame (including 1129 label stack) that fits on the interface to the Downstream LSR. 1131 Address Type 1132 The Address Type indicates if the interface is numbered or 1133 unnumbered. It also determines the length of the Downstream IP 1134 Address and Downstream Interface fields. The resulting total for 1135 the initial part of the TLV is listed in the table below as "K 1136 Octets". The Address Type is set to one of the following values: 1138 Type # Address Type K Octets 1139 ------ ------------ -------- 1140 1 IPv4 Numbered 16 1141 2 IPv4 Unnumbered 16 1142 3 IPv6 Numbered 40 1143 4 IPv6 Unnumbered 28 1145 DS Flags 1147 The DS Flags field is a bit vector with the following format: 1149 0 1 2 3 4 5 6 7 1150 +-+-+-+-+-+-+-+-+ 1151 | Rsvd(MBZ) |I|N| 1152 +-+-+-+-+-+-+-+-+ 1154 Two flags are defined currently, I and N. The remaining flags MUST 1155 be set to zero when sending and ignored on receipt. 1157 Flag Name and Meaning 1158 ---- ---------------- 1159 I Interface and Label Stack Object Request 1161 When this flag is set, it indicates that the replying 1162 router SHOULD include an Interface and Label Stack 1163 Object in the echo reply message. 1165 N Treat as a Non-IP Packet 1167 Echo request messages will be used to diagnose non-IP 1168 flows. However, these messages are carried in IP 1169 packets. For a router that alters its ECMP algorithm 1170 based on the FEC or deep packet examination, this flag 1171 requests that the router treat this as it would if the 1172 determination of an IP payload had failed. 1174 Downstream IP Address and Downstream Interface Address 1176 IPv4 addresses and interface indices are encoded in 4 octets; IPv6 1177 addresses are encoded in 16 octets. 1179 If the interface to the downstream LSR is numbered, then the 1180 Address Type MUST be set to IPv4 or IPv6, the Downstream IP 1181 Address MUST be set to either the downstream LSR's Router ID or 1182 the interface address of the downstream LSR, and the Downstream 1183 Interface Address MUST be set to the downstream LSR's interface 1184 address. 1186 If the interface to the downstream LSR is unnumbered, the Address 1187 Type MUST be IPv4 Unnumbered or IPv6 Unnumbered, the Downstream IP 1188 Address MUST be the downstream LSR's Router ID, and the Downstream 1189 Interface Address MUST be set to the index assigned by the 1190 upstream LSR to the interface. 1192 If an LSR does not know the IP address of its neighbor, then it 1193 MUST set the Address Type to either IPv4 Unnumbered or IPv6 1194 Unnumbered. For IPv4, it must set the Downstream IP Address to 1195 127.0.0.1; for IPv6 the address is set to 0::1. In both cases, 1196 the interface index MUST be set to 0. If an LSR receives an Echo 1197 Request packet with either of these addresses in the Downstream IP 1198 Address field, this indicates that it MUST bypass interface 1199 verification but continue with label validation. 1201 If the originator of an Echo Request packet wishes to obtain 1202 Downstream Mapping information but does not know the expected 1203 label stack, then it SHOULD set the Address Type to either IPv4 1204 Unnumbered or IPv6 Unnumbered. For IPv4, it MUST set the 1205 Downstream IP Address to 224.0.0.2; for IPv6 the address MUST be 1206 set to FF02::2. In both cases, the interface index MUST be set to 1207 0. If an LSR receives an Echo Request packet with the all-routers 1208 multicast address, then this indicates that it MUST bypass both 1209 interface and label stack validation, but return Downstream 1210 Mapping TLVs using the information provided. 1212 Multipath Type 1214 The following Multipath Types are defined: 1216 Key Type Multipath Information 1217 --- ---------------- --------------------- 1218 0 no multipath Empty (Multipath Length = 0) 1219 2 IP address IP addresses 1220 4 IP address range low/high address pairs 1221 8 Bit-masked IP IP address prefix and bit mask 1222 address set 1223 9 Bit-masked label set Label prefix and bit mask 1225 Type 0 indicates that all packets will be forwarded out this one 1226 interface. 1228 Types 2, 4, 8, and 9 specify that the supplied Multipath 1229 Information will serve to exercise this path. 1231 Depth Limit 1233 The Depth Limit is applicable only to a label stack and is the 1234 maximum number of labels considered in the hash; this SHOULD be 1235 set to zero if unspecified or unlimited. 1237 Multipath Length 1239 The length in octets of the Multipath Information. 1241 Multipath Information 1243 Address or label values encoded according to the Multipath Type. 1244 See the next section below for encoding details. 1246 Downstream Label(s) 1248 The set of labels in the label stack as it would have appeared if 1249 this router were forwarding the packet through this interface. 1250 Any Implicit Null labels are explicitly included. Labels are 1251 treated as numbers, i.e., they are right justified in the field. 1253 A Downstream Label is 24 bits, in the same format as an MPLS label 1254 minus the TTL field, i.e., the MSBit of the label is bit 0, the 1255 LSBit is bit 19, the Traffic Class (TC) bits are bits 20-22, and 1256 bit 23 is the S bit. The replying router SHOULD fill in the TC 1257 and S bits; the LSR receiving the echo reply MAY choose to ignore 1258 these bits. Protocol 1260 The Protocol is taken from the following table: 1262 Protocol # Signaling Protocol 1263 ---------- ------------------ 1264 0 Unknown 1265 1 Static 1266 2 BGP 1267 3 LDP 1268 4 RSVP-TE 1270 3.3.1. Multipath Information Encoding 1272 The Multipath Information encodes labels or addresses that will 1273 exercise this path. The Multipath Information depends on the 1274 Multipath Type. The contents of the field are shown in the table 1275 above. IPv4 addresses are drawn from the range 127/8; IPv6 addresses 1276 are drawn from the range 0:0:0:0:0:FFFF:7F00/104. Labels are treated 1277 as numbers, i.e., they are right justified in the field. For Type 4, 1278 ranges indicated by Address pairs MUST NOT overlap and MUST be in 1279 ascending sequence. 1281 Type 8 allows a more dense encoding of IP addresses. The IP prefix 1282 is formatted as a base IP address with the non-prefix low-order bits 1283 set to zero. The maximum prefix length is 27. Following the prefix 1284 is a mask of length 2^(32-prefix length) bits for IPv4 and 1285 2^(128-prefix length) bits for IPv6. Each bit set to 1 represents a 1286 valid address. The address is the base IPv4 address plus the 1287 position of the bit in the mask where the bits are numbered left to 1288 right beginning with zero. For example, the IPv4 addresses 1289 127.2.1.0, 127.2.1.5-127.2.1.15, and 127.2.1.20-127.2.1.29 would be 1290 encoded as follows: 1292 0 1 2 3 1293 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 1294 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1295 |0 1 1 1 1 1 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0| 1296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1297 |1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0 0| 1298 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1300 Those same addresses embedded in IPv6 would be encoded as follows: 1302 0 1 2 3 1303 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 1304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1305 |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0| 1306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1307 |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0| 1308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1309 |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1| 1310 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1311 |0 1 1 1 1 1 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0| 1312 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1313 |1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0 0| 1314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1316 Type 9 allows a more dense encoding of labels. The label prefix is 1317 formatted as a base label value with the non-prefix low-order bits 1318 set to zero. The maximum prefix (including leading zeros due to 1319 encoding) length is 27. Following the prefix is a mask of length 1320 2^(32-prefix length) bits. Each bit set to one represents a valid 1321 label. The label is the base label plus the position of the bit in 1322 the mask where the bits are numbered left to right beginning with 1323 zero. Label values of all the odd numbers between 1152 and 1279 1324 would be encoded as follows: 1326 0 1 2 3 1327 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 1328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1329 |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0| 1330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1331 |0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1| 1332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1333 |0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1| 1334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1335 |0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1| 1336 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1337 |0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1| 1338 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1340 If the received Multipath Information is non-null, the labels and IP 1341 addresses MUST be picked from the set provided. If none of these 1342 labels or addresses map to a particular downstream interface, then 1343 for that interface, the type MUST be set to 0. If the received 1344 Multipath Information is null (i.e., Multipath Length = 0, or for 1345 Types 8 and 9, a mask of all zeros), the type MUST be set to 0. 1347 For example, suppose LSR X at hop 10 has two downstream LSRs, Y and 1348 Z, for the FEC in question. The received X could return Multipath 1349 Type 4, with low/high IP addresses of 127.1.1.1->127.1.1.255 for 1350 downstream LSR Y and 127.2.1.1->127.2.1.255 for downstream LSR Z. 1351 The head end reflects this information to LSR Y. Y, which has three 1352 downstream LSRs, U, V, and W, computes that 127.1.1.1->127.1.1.127 1353 would go to U and 127.1.1.128-> 127.1.1.255 would go to V. Y would 1354 then respond with 3 Downstream Mappings: to U, with Multipath Type 4 1355 (127.1.1.1->127.1.1.127); to V, with Multipath Type 4 1356 (127.1.1.127->127.1.1.255); and to W, with Multipath Type 0. 1358 Note that computing Multipath Information may impose a significant 1359 processing burden on the receiver. A receiver MAY thus choose to 1360 process a subset of the received prefixes. The sender, on receiving 1361 a reply to a Downstream Mapping with partial information, SHOULD 1362 assume that the prefixes missing in the reply were skipped by the 1363 receiver, and MAY re-request information about them in a new echo 1364 request. 1366 3.3.2. Downstream Router and Interface 1368 The notion of "downstream router" and "downstream interface" should 1369 be explained. Consider an LSR X. If a packet that was originated 1370 with TTL n>1 arrived with outermost label L and TTL=1 at LSR X, X 1371 must be able to compute which LSRs could receive the packet if it was 1372 originated with TTL=n+1, over which interface the request would 1373 arrive and what label stack those LSRs would see. (It is outside the 1374 scope of this document to specify how this computation is done.) The 1375 set of these LSRs/interfaces consists of the downstream routers/ 1376 interfaces (and their corresponding labels) for X with respect to L. 1377 Each pair of downstream router and interface requires a separate 1378 Downstream Mapping to be added to the reply. 1380 The case where X is the LSR originating the echo request is a special 1381 case. X needs to figure out what LSRs would receive the MPLS echo 1382 request for a given FEC Stack that X originates with TTL=1. 1384 The set of downstream routers at X may be alternative paths (see the 1385 discussion below on ECMP) or simultaneous paths (e.g., for MPLS 1386 multicast). In the former case, the Multipath Information is used as 1387 a hint to the sender as to how it may influence the choice of these 1388 alternatives. 1390 3.4. Pad TLV 1392 The value part of the Pad TLV contains a variable number (>= 1) of 1393 octets. The first octet takes values from the following table; all 1394 the other octets (if any) are ignored. The receiver SHOULD verify 1395 that the TLV is received in its entirety, but otherwise ignores the 1396 contents of this TLV, apart from the first octet. 1398 Value Meaning 1399 ----- ------- 1400 1 Drop Pad TLV from reply 1401 2 Copy Pad TLV to reply 1402 3-255 Reserved for future use 1404 3.5. Vendor Enterprise Number 1406 SMI Private Enterprise Numbers are maintained by IANA. The Length is 1407 always 4; the value is the SMI Private Enterprise code, in network 1408 octet order, of the vendor with a Vendor Private extension to any of 1409 the fields in the fixed part of the message, in which case this TLV 1410 MUST be present. If none of the fields in the fixed part of the 1411 message have Vendor Private extensions, inclusion of this TLV is 1412 OPTIONAL. Vendor Private ranges for Message Types, Reply Modes, and 1413 Return Codes have been defined. When any of these are used, the 1414 Vendor Enterprise Number TLV MUST be included in the message. 1416 3.6. Interface and Label Stack 1418 The Interface and Label Stack TLV MAY be included in a reply message 1419 to report the interface on which the request message was received and 1420 the label stack that was on the packet when it was received. Only 1421 one such object may appear. The purpose of the object is to allow 1422 the upstream router to obtain the exact interface and label stack 1423 information as it appears at the replying LSR. 1425 The Length is K + 4*N octets; N is the number of labels in the label 1426 stack. Values for K are found in the description of Address Type 1427 below. The Value field of a Downstream Mapping has the following 1428 format: 1430 0 1 2 3 1431 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 1432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1433 | Address Type | Must Be Zero | 1434 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1435 | IP Address (4 or 16 octets) | 1436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1437 | Interface (4 or 16 octets) | 1438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1439 . . 1440 . . 1441 . Label Stack . 1442 . . 1443 . . 1444 . . 1445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1447 Address Type 1449 The Address Type indicates if the interface is numbered or 1450 unnumbered. It also determines the length of the IP Address and 1451 Interface fields. The resulting total for the initial part of the 1452 TLV is listed in the table below as "K Octets". The Address Type 1453 is set to one of the following values: 1455 Type # Address Type K Octets 1456 ------ ------------ -------- 1457 1 IPv4 Numbered 12 1458 2 IPv4 Unnumbered 12 1459 3 IPv6 Numbered 36 1460 4 IPv6 Unnumbered 24 1462 IP Address and Interface 1463 IPv4 addresses and interface indices are encoded in 4 octets; IPv6 1464 addresses are encoded in 16 octets. 1466 If the interface upon which the echo request message was received 1467 is numbered, then the Address Type MUST be set to IPv4 or IPv6, 1468 the IP Address MUST be set to either the LSR's Router ID or the 1469 interface address, and the Interface MUST be set to the interface 1470 address. 1472 If the interface is unnumbered, the Address Type MUST be either 1473 IPv4 Unnumbered or IPv6 Unnumbered, the IP Address MUST be the 1474 LSR's Router ID, and the Interface MUST be set to the index 1475 assigned to the interface. 1477 Label Stack 1479 The label stack of the received echo request message. If any TTL 1480 values have been changed by this router, they SHOULD be restored. 1482 3.7. Errored TLVs 1484 The following TLV is a TLV that MAY be included in an echo reply to 1485 inform the sender of an echo request of mandatory TLVs either not 1486 supported by an implementation or parsed and found to be in error. 1488 The Value field contains the TLVs that were not understood, encoded 1489 as sub-TLVs. 1491 0 1 2 3 1492 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 1493 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1494 | Type = 9 | Length | 1495 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1496 | Value | 1497 . . 1498 . . 1499 . . 1500 | | 1501 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1503 3.8. Reply TOS Byte TLV 1505 This TLV MAY be used by the originator of the echo request to request 1506 that an echo reply be sent with the IP header TOS byte set to the 1507 value specified in the TLV. This TLV has a length of 4 with the 1508 following value field. 1510 0 1 2 3 1511 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 1512 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1513 | Reply-TOS Byte| Must Be Zero | 1514 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1516 4. Theory of Operation 1518 An MPLS echo request is used to test a particular LSP. The LSP to be 1519 tested is identified by the "FEC Stack"; for example, if the LSP was 1520 set up via LDP, and is to an egress IP address of 10.1.1.1, the FEC 1521 Stack contains a single element, namely, an LDP IPv4 prefix sub-TLV 1522 with value 10.1.1.1/32. If the LSP being tested is an RSVP LSP, the 1523 FEC Stack consists of a single element that captures the RSVP Session 1524 and Sender Template that uniquely identifies the LSP. 1526 FEC Stacks can be more complex. For example, one may wish to test a 1527 VPN IPv4 prefix of 10.1/8 that is tunneled over an LDP LSP with 1528 egress 10.10.1.1. The FEC Stack would then contain two sub-TLVs, the 1529 bottom being a VPN IPv4 prefix, and the top being an LDP IPv4 prefix. 1530 If the underlying (LDP) tunnel were not known, or was considered 1531 irrelevant, the FEC Stack could be a single element with just the VPN 1532 IPv4 sub-TLV. 1534 When an MPLS echo request is received, the receiver is expected to 1535 verify that the control plane and data plane are both healthy (for 1536 the FEC Stack being pinged) and that the two planes are in sync. The 1537 procedures for this are in section 4.4 below. 1539 4.1. Dealing with Equal-Cost Multi-Path (ECMP) 1541 LSPs need not be simple point-to-point tunnels. Frequently, a single 1542 LSP may originate at several ingresses, and terminate at several 1543 egresses; this is very common with LDP LSPs. LSPs for a given FEC 1544 may also have multiple "next hops" at transit LSRs. At an ingress, 1545 there may also be several different LSPs to choose from to get to the 1546 desired endpoint. Finally, LSPs may have backup paths, detour paths, 1547 and other alternative paths to take should the primary LSP go down. 1549 To deal with the last two first: it is assumed that the LSR sourcing 1550 MPLS echo requests can force the echo request into any desired LSP, 1551 so choosing among multiple LSPs at the ingress is not an issue. The 1552 problem of probing the various flavors of backup paths that will 1553 typically not be used for forwarding data unless the primary LSP is 1554 down will not be addressed here. 1556 Since the actual LSP and path that a given packet may take may not be 1557 known a priori, it is useful if MPLS echo requests can exercise all 1558 possible paths. This, although desirable, may not be practical, 1559 because the algorithms that a given LSR uses to distribute packets 1560 over alternative paths may be proprietary. 1562 To achieve some degree of coverage of alternate paths, there is a 1563 certain latitude in choosing the destination IP address and source 1564 UDP port for an MPLS echo request. This is clearly not sufficient; 1565 in the case of traceroute, more latitude is offered by means of the 1566 Multipath Information of the Downstream Mapping TLV. This is used as 1567 follows. An ingress LSR periodically sends an MPLS traceroute 1568 message to determine whether there are multipaths for a given LSP. 1569 If so, each hop will provide some information how each of its 1570 downstream paths can be exercised. The ingress can then send MPLS 1571 echo requests that exercise these paths. If several transit LSRs 1572 have ECMP, the ingress may attempt to compose these to exercise all 1573 possible paths. However, full coverage may not be possible. 1575 4.2. Testing LSPs That Are Used to Carry MPLS Payloads 1577 To detect certain LSP breakages, it may be necessary to encapsulate 1578 an MPLS echo request packet with at least one additional label when 1579 testing LSPs that are used to carry MPLS payloads (such as LSPs used 1580 to carry L2VPN and L3VPN traffic. For example, when testing LDP or 1581 RSVP-TE LSPs, just sending an MPLS echo request packet may not detect 1582 instances where the router immediately upstream of the destination of 1583 the LSP ping may forward the MPLS echo request successfully over an 1584 interface not configured to carry MPLS payloads because of the use of 1585 penultimate hop popping. Since the receiving router has no means to 1586 differentiate whether the IP packet was sent unlabeled or implicitly 1587 labeled, the addition of labels shimmed above the MPLS echo request 1588 (using the Nil FEC) will prevent a router from forwarding such a 1589 packet out unlabeled interfaces. 1591 4.3. Sending an MPLS Echo Request 1593 An MPLS echo request is a UDP packet. The IP header is set as 1594 follows: the source IP address is a routable address of the sender; 1595 the destination IP address is a (randomly chosen) IPv4 address from 1596 the range 127/8 or IPv6 address from the range 1597 0:0:0:0:0:FFFF:7F00/104. The IP TTL is set to 1. The source UDP 1598 port is chosen by the sender; the destination UDP port is set to 3503 1599 (assigned by IANA for MPLS echo requests). The Router Alert IP 1600 option of value 0x0 [RFC2113] for IPv4 or value 69 [RFC7506] for IPv6 1601 MUST be set in IP header. 1603 An MPLS echo request is sent with a label stack corresponding to the 1604 FEC Stack being tested. Note that further labels could be applied 1605 if, for example, the normal route to the topmost FEC in the stack is 1606 via a Traffic Engineered Tunnel [RFC3209]. If all of the FECs in the 1607 stack correspond to Implicit Null labels, the MPLS echo request is 1608 considered unlabeled even if further labels will be applied in 1609 sending the packet. 1611 If the echo request is labeled, one MAY (depending on what is being 1612 pinged) set the TTL of the innermost label to 1, to prevent the ping 1613 request going farther than it should. Examples of where this SHOULD 1614 be done include pinging a VPN IPv4 or IPv6 prefix, an L2 VPN endpoint 1615 or a pseudowire. Preventing the ping request from going too far can 1616 also be accomplished by inserting a Router Alert label above this 1617 label; however, this may lead to the undesired side effect that MPLS 1618 echo requests take a different data path than actual data. For more 1619 information on how these mechanisms can be used for pseudowire 1620 connectivity verification, see [RFC5085]. 1622 In "ping" mode (end-to-end connectivity check), the TTL in the 1623 outermost label is set to 255. In "traceroute" mode (fault isolation 1624 mode), the TTL is set successively to 1, 2, and so on. 1626 The sender chooses a Sender's Handle and a Sequence Number. When 1627 sending subsequent MPLS echo requests, the sender SHOULD increment 1628 the Sequence Number by 1. However, a sender MAY choose to send a 1629 group of echo requests with the same Sequence Number to improve the 1630 chance of arrival of at least one packet with that Sequence Number. 1632 The TimeStamp Sent is set to the time-of-day in NTP format that the 1633 echo request is sent. The TimeStamp Received is set to zero. 1635 An MPLS echo request MUST have an FEC Stack TLV. Also, the Reply 1636 Mode must be set to the desired reply mode; the Return Code and 1637 Subcode are set to zero. In the "traceroute" mode, the echo request 1638 SHOULD include a Downstream Mapping TLV. 1640 4.4. Receiving an MPLS Echo Request 1642 Sending an MPLS echo request to the control plane is triggered by one 1643 of the following packet processing exceptions: Router Alert option, 1644 IP TTL expiration, MPLS TTL expiration, MPLS Router Alert label, or 1645 the destination address in the 127/8 address range. The control 1646 plane further identifies it by UDP destination port 3503. 1648 For reporting purposes the bottom of stack is considered to be stack- 1649 depth of 1. This is to establish an absolute reference for the case 1650 where the actual stack may have more labels than there are FECs in 1651 the Target FEC Stack. 1653 Furthermore, in all the error codes listed in this document, a stack- 1654 depth of 0 means "no value specified". This allows compatibility 1655 with existing implementations that do not use the Return Subcode 1656 field. 1658 An LSR X that receives an MPLS echo request then processes it as 1659 follows. 1661 1. General packet sanity is verified. If the packet is not well- 1662 formed, LSR X SHOULD send an MPLS Echo Reply with the Return Code 1663 set to "Malformed echo request received" and the Subcode to zero. 1664 If there are any TLVs not marked as "Ignore" that LSR X does not 1665 understand, LSR X SHOULD send an MPLS "TLV not understood" (as 1666 appropriate), and the Subcode set to zero. In the latter case, 1667 the misunderstood TLVs (only) are included as sub-TLVs in an 1668 Errored TLVs TLV in the reply. The header fields Sender's 1669 Handle, Sequence Number, and Timestamp Sent are not examined, but 1670 are included in the MPLS echo reply message. 1672 The algorithm uses the following variables and identifiers: 1674 Interface-I: the interface on which the MPLS echo request was 1675 received. 1677 Stack-R: the label stack on the packet as it was received. 1679 Stack-D: the label stack carried in the Downstream Mapping 1680 TLV (not always present) 1682 Label-L: the label from the actual stack currently being 1683 examined. Requires no initialization. 1685 Label-stack-depth: the depth of label being verified. Initialized 1686 to the number of labels in the received label 1687 stack S. 1689 FEC-stack-depth: depth of the FEC in the Target FEC Stack that 1690 should be used to verify the current actual 1691 label. Requires no initialization. 1693 Best-return-code: contains the return code for the echo reply 1694 packet as currently best known. As the algorithm 1695 progresses, this code may change depending on the 1696 results of further checks that it performs. 1698 Best-rtn-subcode: similar to Best-return-code, but for the Echo 1699 Reply Subcode. 1701 FEC-status: result value returned by the FEC Checking 1702 algorithm described in section 4.4.1. 1704 /* Save receive context information */ 1706 2. If the echo request is good, LSR X stores the interface over 1707 which the echo was received in Interface-I, and the label stack 1708 with which it came in Stack-R. 1710 /* The rest of the algorithm iterates over the labels in Stack-R, 1711 verifies validity of label values, reports associated label switching 1712 operations (for traceroute), verifies correspondence between the 1713 Stack-R and the Target FEC Stack description in the body of the echo 1714 request, and reports any errors. */ 1716 /* The algorithm iterates as follows. */ 1718 3. Label Validation: 1720 If Label-stack-depth is 0 { 1722 /* The LSR needs to report its being a tail-end for the LSP */ 1724 Set FEC-stack-depth to 1, set Label-L to 3 (Implicit Null). 1725 Set Best-return-code to 3 ("Replying router is an egress for 1726 the FEC at stack depth"), set Best-rtn-subcode to the value of 1727 FEC-stack-depth (1) and go to step 5 (Egress Processing). 1729 } 1731 /* This step assumes there is always an entry for well-known label 1732 values */ 1734 Set Label-L to the value extracted from Stack-R at depth Label- 1735 stack-depth. Look up Label-L in the Incoming Label Map (ILM) to 1736 determine if the label has been allocated and an operation is 1737 associated with it. 1739 If there is no entry for L { 1741 /* Indicates a temporary or permanent label synchronization 1742 problem the LSR needs to report an error */ 1744 Set Best-return-code to 11 ("No label entry at stack-depth") 1745 and Best-rtn-subcode to Label-stack-depth. Go to step 7 (Send 1746 Reply Packet). 1748 } 1749 Else { 1751 Retrieve the associated label operation from the corresponding 1752 NHLFE and proceed to step 4 (Label Operation check). 1754 } 1756 4. Label Operation Check 1758 If the label operation is "Pop and Continue Processing" { 1760 /* Includes Explicit Null and Router Alert label cases */ 1762 Iterate to the next label by decrementing Label-stack-depth and 1763 loop back to step 3 (Label Validation). 1765 } 1767 If the label operation is "Swap or Pop and Switch based on Popped 1768 Label" { 1770 Set Best-return-code to 8 ("Label switched at stack-depth") and 1771 Best-rtn-subcode to Label-stack-depth to report transit 1772 switching. 1774 If a Downstream Mapping TLV is present in the received echo 1775 request { 1777 If the IP address in the TLV is 127.0.0.1 or 0::1 { 1779 Set Best-return-code to 6 ("Upstream Interface Index 1780 Unknown"). An Interface and Label Stack TLV SHOULD be 1781 included in the reply and filled with Interface-I and 1782 Stack-R. 1784 } 1786 Else { 1788 Verify that the IP address, interface address, and label 1789 stack in the Downstream Mapping TLV match Interface-I and 1790 Stack-R. If there is a mismatch, set Best-return-code to 1791 5, "Downstream Mapping Mismatch". An Interface and Label 1792 Stack TLV SHOULD be included in the reply and filled in 1793 based on Interface-I and Stack-R. Go to step 7 (Send 1794 Reply Packet). 1796 } 1798 } 1800 For each available downstream ECMP path { 1802 Retrieve output interface from the NHLFE entry. 1804 /* Note: this return code is set even if Label-stack-depth 1805 is one */ 1807 If the output interface is not MPLS enabled { 1809 Set Best-return-code to Return Code 9, "Label switched 1810 but no MPLS forwarding at stack-depth" and set Best-rtn- 1811 subcode to Label-stack-depth and goto Send_Reply_Packet. 1813 } 1815 If a Downstream Mapping TLV is present { 1817 A Downstream Mapping TLV SHOULD be included in the echo 1818 reply (see section 3.3) filled in with information about 1819 the current ECMP path. 1821 } 1823 } 1825 If no Downstream Mapping TLV is present, or the Downstream IP 1826 Address is set to the ALLROUTERS multicast address, go to step 1827 7 (Send Reply Packet). 1829 If the "Validate FEC Stack" flag is not set and the LSR is not 1830 configured to perform FEC checking by default, go to step 7 1831 (Send Reply Packet). 1833 /* Validate the Target FEC Stack in the received echo request. 1835 First determine FEC-stack-depth from the Downstream Mapping 1836 TLV. This is done by walking through Stack-D (the Downstream 1837 labels) from the bottom, decrementing the number of labels for 1838 each non-Implicit Null label, while incrementing FEC-stack- 1839 depth for each label. If the Downstream Mapping TLV contains 1840 one or more Implicit Null labels, FEC-stack-depth may be 1841 greater than Label-stack-depth. To be consistent with the 1842 above stack-depths, the bottom is considered to be entry 1. 1843 */ 1845 Set FEC-stack-depth to 0. Set i to Label-stack-depth. 1847 While (i > 0 ) do { 1849 ++FEC-stack-depth. 1850 if Stack-D[FEC-stack-depth] != 3 (Implicit Null) 1851 --i. 1852 } 1854 If the number of FECs in the FEC stack is greater than or equal 1855 to FEC-stack-depth { 1856 Perform the FEC Checking procedure (see subsection 4.4.1 1857 below). 1859 If FEC-status is 2, set Best-return-code to 10 ("Mapping for 1860 this FEC is not the given label at stack-depth"). 1862 If the return code is 1, set Best-return-code to FEC-return- 1863 code and Best-rtn-subcode to FEC-stack-depth. 1864 } 1866 Go to step 7 (Send Reply Packet). 1867 } 1869 5. Egress Processing: 1871 /* These steps are performed by the LSR that identified itself as 1872 the tail-end LSR for an LSP. */ 1874 If received echo request contains no Downstream Mapping TLV, or 1875 the Downstream IP Address is set to 127.0.0.1 or 0::1 go to step 6 1876 (Egress FEC Validation). 1878 Verify that the IP address, interface address, and label stack in 1879 the Downstream Mapping TLV match Interface-I and Stack-R. If not, 1880 set Best-return-code to 5, "Downstream Mapping Mis-match". A 1881 Received Interface and Label Stack TLV SHOULD be created for the 1882 echo response packet. Go to step 7 (Send Reply Packet). 1884 6. Egress FEC Validation: 1886 /* This is a loop for all entries in the Target FEC Stack starting 1887 with FEC-stack-depth. */ 1889 Perform FEC checking by following the algorithm described in 1890 subsection 4.4.1 for Label-L and the FEC at FEC-stack-depth. 1892 Set Best-return-code to FEC-code and Best-rtn-subcode to the value 1893 in FEC-stack-depth. 1895 If FEC-status (the result of the check) is 1, 1896 go to step 7 (Send Reply Packet). 1898 /* Iterate to the next FEC entry */ 1900 ++FEC-stack-depth. 1901 If FEC-stack-depth > the number of FECs in the FEC-stack, 1902 go to step 7 (Send Reply Packet). 1904 If FEC-status is 0 { 1906 ++Label-stack-depth. 1907 If Label-stack-depth > the number of labels in Stack-R, 1908 Go to step 7 (Send Reply Packet). 1910 Label-L = extracted label from Stack-R at depth 1911 Label-stack-depth. 1912 Loop back to step 6 (Egress FEC Validation). 1913 } 1915 7. Send Reply Packet: 1917 Send an MPLS echo reply with a Return Code of Best-return-code, 1918 and a Return Subcode of Best-rtn-subcode. Include any TLVs 1919 created during the above process. The procedures for sending the 1920 echo reply are found in subsection 4.5. 1922 4.4.1. FEC Validation 1924 /* This subsection describes validation of an FEC entry within the 1925 Target FEC Stack and accepts an FEC, Label-L, and Interface-I. The 1926 algorithm performs the following steps. */ 1928 1. Two return values, FEC-status and FEC-return-code, are 1929 initialized to 0. 1931 2. If the FEC is the Nil FEC { 1933 If Label-L is either Explicit_Null or Router_Alert, return. 1935 Else { 1937 Set FEC-return-code to 10 ("Mapping for this FEC is not the 1938 given label at stack-depth"). 1939 Set FEC-status to 1 1940 Return. 1941 } 1943 } 1945 3. Check the FEC label mapping that describes how traffic received 1946 on the LSP is further switched or which application it is 1947 associated with. If no mapping exists, set FEC-return-code to 1948 Return 4, "Replying router has no mapping for the FEC at stack- 1949 depth". Set FEC-status to 1. Return. 1951 4. If the label mapping for FEC is Implicit Null, set FEC-status to 1952 2 and proceed to step 5. Otherwise, if the label mapping for FEC 1953 is Label-L, proceed to step 5. Otherwise, set FEC-return-code to 1954 10 ("Mapping for this FEC is not the given label at stack- 1955 depth"), set FEC-status to 1, and return. 1957 5. This is a protocol check. Check what protocol would be used to 1958 advertise FEC. If it can be determined that no protocol 1959 associated with Interface-I would have advertised an FEC of that 1960 FEC-Type, set FEC-return-code to 12 ("Protocol not associated 1961 with interface at FEC stack-depth"). Set FEC-status to 1. 1963 6. Return. 1965 4.5. Sending an MPLS Echo Reply 1967 An MPLS echo reply is a UDP packet. It MUST ONLY be sent in response 1968 to an MPLS echo request. The source IP address is a routable address 1969 of the replier; the source port is the well-known UDP port for LSP 1970 ping. The destination IP address and UDP port are copied from the 1971 source IP address and UDP port of the echo request. The IP TTL is 1972 set to 255. If the Reply Mode in the echo request is "Reply via an 1973 IPv4 UDP packet with Router Alert", then the IP header MUST contain 1974 the Router Alert IP option of value 0x0 [RFC2113] for IPv4 or 69 1975 [RFC7506] for IPv6. If the reply is sent over an LSP, the topmost 1976 label MUST in this case be the Router Alert label (1) (see 1977 [RFC3032]). 1979 The format of the echo reply is the same as the echo request. The 1980 Sender's Handle, the Sequence Number, and TimeStamp Sent are copied 1981 from the echo request; the TimeStamp Received is set to the time-of- 1982 day that the echo request is received (note that this information is 1983 most useful if the time-of-day clocks on the requester and the 1984 replier are synchronized). The FEC Stack TLV from the echo request 1985 MAY be copied to the reply. 1987 The replier MUST fill in the Return Code and Subcode, as determined 1988 in the previous subsection. 1990 If the echo request contains a Pad TLV, the replier MUST interpret 1991 the first octet for instructions regarding how to reply. 1993 If the replying router is the destination of the FEC, then Downstream 1994 Mapping TLVs SHOULD NOT be included in the echo reply. 1996 If the echo request contains a Downstream Mapping TLV, and the 1997 replying router is not the destination of the FEC, the replier SHOULD 1998 compute its downstream routers and corresponding labels for the 1999 incoming label, and add Downstream Mapping TLVs for each one to the 2000 echo reply it sends back. 2002 If the Downstream Mapping TLV contains Multipath Information 2003 requiring more processing than the receiving router is willing to 2004 perform, the responding router MAY choose to respond with only a 2005 subset of multipaths contained in the echo request Downstream 2006 Mapping. (Note: The originator of the echo request MAY send another 2007 echo request with the Multipath Information that was not included in 2008 the reply.) 2010 Except in the case of Reply Mode 4, "Reply via application level 2011 control channel", echo replies are always sent in the context of the 2012 IP/MPLS network. 2014 4.6. Receiving an MPLS Echo Reply 2016 An LSR X should only receive an MPLS echo reply in response to an 2017 MPLS echo request that it sent. Thus, on receipt of an MPLS echo 2018 reply, X should parse the packet to ensure that it is well-formed, 2019 then attempt to match up the echo reply with an echo request that it 2020 had previously sent, using the destination UDP port and the Sender's 2021 Handle. If no match is found, then X jettisons the echo reply; 2022 otherwise, it checks the Sequence Number to see if it matches. 2024 If the echo reply contains Downstream Mappings, and X wishes to 2025 traceroute further, it SHOULD copy the Downstream Mapping(s) into its 2026 next echo request(s) (with TTL incremented by one). 2028 4.7. Issue with VPN IPv4 and IPv6 Prefixes 2030 Typically, an LSP ping for a VPN IPv4 prefix or VPN IPv6 prefix is 2031 sent with a label stack of depth greater than 1, with the innermost 2032 label having a TTL of 1. This is to terminate the ping at the egress 2033 PE, before it gets sent to the customer device. However, under 2034 certain circumstances, the label stack can shrink to a single label 2035 before the ping hits the egress PE; this will result in the ping 2036 terminating prematurely. One such scenario is a multi-AS Carrier's 2037 Carrier VPN. 2039 To get around this problem, one approach is for the LSR that receives 2040 such a ping to realize that the ping terminated prematurely, and send 2041 back error code 13. In that case, the initiating LSR can retry the 2042 ping after incrementing the TTL on the VPN label. In this fashion, 2043 the ingress LSR will sequentially try TTL values until it finds one 2044 that allows the VPN ping to reach the egress PE. 2046 4.8. Non-compliant Routers 2048 If the egress for the FEC Stack being pinged does not support MPLS 2049 ping, then no reply will be sent, resulting in possible "false 2050 negatives". If in "traceroute" mode, a transit LSR does not support 2051 LSP ping, then no reply will be forthcoming from that LSR for some 2052 TTL, say, n. The LSR originating the echo request SHOULD try sending 2053 the echo request with TTL=n+1, n+2, ..., n+k to probe LSRs further 2054 down the path. In such a case, the echo request for TTL > n SHOULD 2055 be sent with Downstream Mapping TLV "Downstream IP Address" field set 2056 to the ALLROUTERs multicast address until a reply is received with a 2057 Downstream Mapping TLV. The label stack MAY be omitted from the 2058 Downstream Mapping TLV. Furthermore, the "Validate FEC Stack" flag 2059 SHOULD NOT be set until an echo reply packet with a Downstream 2060 Mapping TLV is received. 2062 5. Security Considerations 2064 Overall, the security needs for LSP ping are similar to those of ICMP 2065 ping. 2067 There are at least three approaches to attacking LSRs using the 2068 mechanisms defined here. One is a Denial-of-Service attack, by 2069 sending MPLS echo requests/replies to LSRs and thereby increasing 2070 their workload. The second is obfuscating the state of the MPLS data 2071 plane liveness by spoofing, hijacking, replaying, or otherwise 2072 tampering with MPLS echo requests and replies. The third is an 2073 unauthorized source using an LSP ping to obtain information about the 2074 network. 2076 To avoid potential Denial-of-Service attacks, it is RECOMMENDED that 2077 implementations regulate the LSP ping traffic going to the control 2078 plane. A rate limiter SHOULD be applied to the well-known UDP port 2079 defined below. 2081 Unsophisticated replay and spoofing attacks involving faking or 2082 replaying MPLS echo reply messages are unlikely to be effective. 2083 These replies would have to match the Sender's Handle and Sequence 2084 Number of an outstanding MPLS echo request message. A non-matching 2085 replay would be discarded as the sequence has moved on, thus a spoof 2086 has only a small window of opportunity. However, to provide a 2087 stronger defense, an implementation MAY also validate the TimeStamp 2088 Sent by requiring an exact match on this field. 2090 To protect against unauthorized sources using MPLS echo request 2091 messages to obtain network information, it is RECOMMENDED that 2092 implementations provide a means of checking the source addresses of 2093 MPLS echo request messages against an access list before accepting 2094 the message. 2096 It is not clear how to prevent hijacking (non-delivery) of echo 2097 requests or replies; however, if these messages are indeed hijacked, 2098 LSP ping will report that the data plane is not working as it should. 2100 It does not seem vital (at this point) to secure the data carried in 2101 MPLS echo requests and replies, although knowledge of the state of 2102 the MPLS data plane may be considered confidential by some. 2103 Implementations SHOULD, however, provide a means of filtering the 2104 addresses to which echo reply messages may be sent. 2106 Although this document makes special use of 127/8 address, these are 2107 used only in conjunction with the UDP port 3503. Furthermore, these 2108 packets are only processed by routers. All other hosts MUST treat 2109 all packets with a destination address in the range 127/8 in 2110 accordance to RFC 1122. Any packet received by a router with a 2111 destination address in the range 127/8 without a destination UDP port 2112 of 3503 MUST be treated in accordance to RFC 1812. In particular, 2113 the default behavior is to treat packets destined to a 127/8 address 2114 as "martians". 2116 6. IANA Considerations 2118 The TCP and UDP port number 3503 has been allocated by IANA for LSP 2119 echo requests and replies. 2121 The following sections detail the new name spaces to be managed by 2122 IANA. For each of these name spaces, the space is divided into 2123 assignment ranges; the following terms are used in describing the 2124 procedures by which IANA allocates values: "Standards Action" (as 2125 defined in [RFC5226]), "Specification Required", and "Vendor Private 2126 Use". 2128 Values from "Specification Required" ranges MUST be registered with 2129 IANA. The request MUST be made via an Experimental RFC that 2130 describes the format and procedures for using the code point; the 2131 actual assignment is made during the IANA actions for the RFC. 2133 Values from "Vendor Private" ranges MUST NOT be registered with IANA; 2134 however, the message MUST contain an enterprise code as registered 2135 with the IANA SMI Private Network Management Private Enterprise 2136 Numbers. For each name space that has a Vendor Private range, it 2137 must be specified where exactly the SMI Private Enterprise Number 2138 resides; see below for examples. In this way, several enterprises 2139 (vendors) can use the same code point without fear of collision. 2141 6.1. Message Types, Reply Modes, Return Codes 2143 The IANA has created and will maintain registries for Message Types, 2144 Reply Modes, and Return Codes. Each of these can take values in the 2145 range 0-255. Assignments in the range 0-191 are via Standards 2146 Action; assignments in the range 192-251 are made via "Specification 2147 Required"; values in the range 252-255 are for Vendor Private Use, 2148 and MUST NOT be allocated. 2150 If any of these fields fall in the Vendor Private range, a top-level 2151 Vendor Enterprise Number TLV MUST be present in the message. 2153 Message Types defined in this document are the following: 2155 Value Meaning 2156 ----- ------- 2157 1 MPLS echo request 2158 2 MPLS echo reply 2160 Reply Modes defined in this document are the following: 2162 Value Meaning 2163 ----- ------- 2164 1 Do not reply 2165 2 Reply via an IPv4/IPv6 UDP packet 2166 3 Reply via an IPv4/IPv6 UDP packet with Router Alert 2167 4 Reply via application level control channel 2169 Return Codes defined in this document are listed in section 3.1. 2171 6.2. TLVs 2173 The IANA has created and will maintain a registry for the Type field 2174 of top-level TLVs as well as for any associated sub-TLVs. Note the 2175 meaning of a sub-TLV is scoped by the TLV. The number spaces for the 2176 sub-TLVs of various TLVs are independent. 2178 The valid range for TLVs and sub-TLVs is 0-65535. Assignments in the 2179 range 0-16383 and 32768-49161 are made via Standards Action as 2180 defined in [RFC5226]; assignments in the range 16384-31743 and 2181 49162-64511 are made via "Specification Required" as defined above; 2182 values in the range 31744-32767 and 64512-65535 are for Vendor 2183 Private Use, and MUST NOT be allocated. 2185 If a TLV or sub-TLV has a Type that falls in the range for Vendor 2186 Private Use, the Length MUST be at least 4, and the first four octets 2187 MUST be that vendor's SMI Private Enterprise Number, in network octet 2188 order. The rest of the Value field is private to the vendor. 2190 TLVs and sub-TLVs defined in this document are the following: 2192 Type Sub-Type Value Field 2193 ---- -------- ----------- 2194 1 Target FEC Stack 2195 1 LDP IPv4 prefix 2196 2 LDP IPv6 prefix 2197 3 RSVP IPv4 LSP 2198 4 RSVP IPv6 LSP 2199 5 Not Assigned 2200 6 VPN IPv4 prefix 2201 7 VPN IPv6 prefix 2202 8 L2 VPN endpoint 2203 9 "FEC 128" Pseudowire - IPv4 (Deprecated) 2204 10 "FEC 128" Pseudowire - IPv4 2205 11 "FEC 129" Pseudowire - IPv4 2206 12 BGP labeled IPv4 prefix 2207 13 BGP labeled IPv6 prefix 2208 14 Generic IPv4 prefix 2209 15 Generic IPv6 prefix 2210 16 Nil FEC 2211 24 "FEC 128" Pseudowire - IPv6 2212 25 "FEC 129" Pseudowire - IPv6 2213 2 Downstream Mapping 2214 3 Pad 2215 4 Not Assigned 2216 5 Vendor Enterprise Number 2217 6 Not Assigned 2218 7 Interface and Label Stack 2219 8 Not Assigned 2220 9 Errored TLVs 2221 Any value The TLV not understood 2222 10 Reply TOS Byte 2224 7. Acknowledgements 2226 The original acknowledgements from RFC 4379 state the following: 2228 This document is the outcome of many discussions among many 2229 people, including Manoj Leelanivas, Paul Traina, Yakov Rekhter, 2230 Der-Hwa Gan, Brook Bailey, Eric Rosen, Ina Minei, Shivani 2231 Aggarwal, and Vanson Lim. 2233 The description of the Multipath Information sub-field of the 2234 Downstream Mapping TLV was adapted from text suggested by Curtis 2235 Villamizar. 2237 We would like to thank Loa Andersson for motivating the advancement 2238 of this bis specification. We also would like to thank Alexander 2239 Vainshtein for his review and comments. 2241 8. References 2243 8.1. Normative References 2245 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 2246 Communication Layers", STD 3, RFC 1122, 2247 DOI 10.17487/RFC1122, October 1989, 2248 . 2250 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 2251 RFC 1812, DOI 10.17487/RFC1812, June 1995, 2252 . 2254 [RFC2113] Katz, D., "IP Router Alert Option", RFC 2113, 2255 DOI 10.17487/RFC2113, February 1997, 2256 . 2258 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2259 Requirement Levels", BCP 14, RFC 2119, 2260 DOI 10.17487/RFC2119, March 1997, 2261 . 2263 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., 2264 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack 2265 Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, 2266 . 2268 [RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual 2269 Private Network (VPN) Terminology", RFC 4026, 2270 DOI 10.17487/RFC4026, March 2005, 2271 . 2273 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 2274 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 2275 DOI 10.17487/RFC4271, January 2006, 2276 . 2278 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 2279 Label Switched (MPLS) Data Plane Failures", RFC 4379, 2280 DOI 10.17487/RFC4379, February 2006, 2281 . 2283 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 2284 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 2285 DOI 10.17487/RFC5226, May 2008, 2286 . 2288 [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, 2289 "Network Time Protocol Version 4: Protocol and Algorithms 2290 Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, 2291 . 2293 [RFC7506] Raza, K., Akiya, N., and C. Pignataro, "IPv6 Router Alert 2294 Option for MPLS Operations, Administration, and 2295 Maintenance (OAM)", RFC 7506, DOI 10.17487/RFC7506, April 2296 2015, . 2298 8.2. Informative References 2300 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 2301 RFC 792, DOI 10.17487/RFC0792, September 1981, 2302 . 2304 [RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in 2305 BGP-4", RFC 3107, DOI 10.17487/RFC3107, May 2001, 2306 . 2308 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 2309 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 2310 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 2311 . 2313 [RFC4365] Rosen, E., "Applicability Statement for BGP/MPLS IP 2314 Virtual Private Networks (VPNs)", RFC 4365, 2315 DOI 10.17487/RFC4365, February 2006, 2316 . 2318 [RFC4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and 2319 G. Heron, "Pseudowire Setup and Maintenance Using the 2320 Label Distribution Protocol (LDP)", RFC 4447, 2321 DOI 10.17487/RFC4447, April 2006, 2322 . 2324 [RFC4761] Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private 2325 LAN Service (VPLS) Using BGP for Auto-Discovery and 2326 Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007, 2327 . 2329 [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., 2330 "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, 2331 October 2007, . 2333 [RFC5085] Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual 2334 Circuit Connectivity Verification (VCCV): A Control 2335 Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085, 2336 December 2007, . 2338 Authors' Addresses 2340 Carlos Pignataro 2341 Cisco Systems, Inc. 2343 Email: cpignata@cisco.com 2345 Nagendra Kumar 2346 Cisco Systems, Inc. 2348 Email: naikumar@cisco.com 2350 Sam Aldrin 2351 Google 2353 Email: aldrin.ietf@gmail.com 2355 Mach(Guoyi) Chen 2356 Huawei 2358 Email: mach.chen@huawei.com