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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 1742, 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: 3 errors (**), 0 flaws (~~), 5 warnings (==), 4 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 (if approved) Cisco 5 Intended status: Standards Track S. Aldrin 6 Expires: March 29, 2016 Google 7 M. Chen 8 Huawei 9 September 26, 2015 11 Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures 12 draft-smack-mpls-rfc4379bis-01.txt 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 March 29, 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 . . . . . . . . . . . . . . . . . . . . . . 3 61 1.2. Structure of This Document . . . . . . . . . . . . . . . 4 62 1.3. Contributors . . . . . . . . . . . . . . . . . . . . . . 4 63 1.4. Scope of RFC4379bis work . . . . . . . . . . . . . . . . 4 64 1.5. ToDo . . . . . . . . . . . . . . . . . . . . . . . . . . 5 65 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 2.1. Use of Address Range 127/8 . . . . . . . . . . . . . . . 6 67 3. Packet Format . . . . . . . . . . . . . . . . . . . . . . . 7 68 3.1. Return Codes . . . . . . . . . . . . . . . . . . . . . . 12 69 3.2. Target FEC Stack . . . . . . . . . . . . . . . . . . . . 12 70 3.2.1. LDP IPv4 Prefix . . . . . . . . . . . . . . . . . . 14 71 3.2.2. LDP IPv6 Prefix . . . . . . . . . . . . . . . . . . 14 72 3.2.3. RSVP IPv4 LSP . . . . . . . . . . . . . . . . . . . 14 73 3.2.4. RSVP IPv6 LSP . . . . . . . . . . . . . . . . . . . 15 74 3.2.5. VPN IPv4 Prefix . . . . . . . . . . . . . . . . . . 15 75 3.2.6. VPN IPv6 Prefix . . . . . . . . . . . . . . . . . . 16 76 3.2.7. L2 VPN Endpoint . . . . . . . . . . . . . . . . . . 17 77 3.2.8. FEC 128 Pseudowire (Deprecated) . . . . . . . . . . 17 78 3.2.9. FEC 128 Pseudowire (Current) . . . . . . . . . . . . 18 79 3.2.10. FEC 129 Pseudowire . . . . . . . . . . . . . . . . . 19 80 3.2.11. BGP Labeled IPv4 Prefix . . . . . . . . . . . . . . 20 81 3.2.12. BGP Labeled IPv6 Prefix . . . . . . . . . . . . . . 20 82 3.2.13. Generic IPv4 Prefix . . . . . . . . . . . . . . . . 21 83 3.2.14. Generic IPv6 Prefix . . . . . . . . . . . . . . . . 21 84 3.2.15. Nil FEC . . . . . . . . . . . . . . . . . . . . . . 22 85 3.3. Downstream Mapping . . . . . . . . . . . . . . . . . . . 22 86 3.3.1. Multipath Information Encoding . . . . . . . . . . . 26 87 3.3.2. Downstream Router and Interface . . . . . . . . . . 28 88 3.4. Pad TLV . . . . . . . . . . . . . . . . . . . . . . . . 29 89 3.5. Vendor Enterprise Number . . . . . . . . . . . . . . . . 29 90 3.6. Interface and Label Stack . . . . . . . . . . . . . . . 29 91 3.7. Errored TLVs . . . . . . . . . . . . . . . . . . . . . . 31 92 3.8. Reply TOS Byte TLV . . . . . . . . . . . . . . . . . . . 31 93 4. Theory of Operation . . . . . . . . . . . . . . . . . . . . 32 94 4.1. Dealing with Equal-Cost Multi-Path (ECMP) . . . . . . . 32 95 4.2. Testing LSPs That Are Used to Carry MPLS Payloads . . . 33 96 4.3. Sending an MPLS Echo Request . . . . . . . . . . . . . . 33 97 4.4. Receiving an MPLS Echo Request . . . . . . . . . . . . . 34 98 4.4.1. FEC Validation . . . . . . . . . . . . . . . . . . . 40 99 4.5. Sending an MPLS Echo Reply . . . . . . . . . . . . . . . 41 100 4.6. Receiving an MPLS Echo Reply . . . . . . . . . . . . . . 42 101 4.7. Issue with VPN IPv4 and IPv6 Prefixes . . . . . . . . . 42 102 4.8. Non-compliant Routers . . . . . . . . . . . . . . . . . 43 103 5. Security Considerations . . . . . . . . . . . . . . . . . . 43 104 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . 44 105 6.1. Message Types, Reply Modes, Return Codes . . . . . . . . 45 106 6.2. TLVs . . . . . . . . . . . . . . . . . . . . . . . . . . 45 107 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 46 108 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 47 109 8.1. Normative References . . . . . . . . . . . . . . . . . . 47 110 8.2. Informative References . . . . . . . . . . . . . . . . . 48 111 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48 113 1. Introduction 115 This document describes a simple and efficient mechanism that can be 116 used to detect data plane failures in MPLS Label Switched Paths 117 (LSPs). There are two parts to this document: information carried in 118 an MPLS "echo request" and "echo reply", and mechanisms for 119 transporting the echo reply. The first part aims at providing enough 120 information to check correct operation of the data plane, as well as 121 a mechanism to verify the data plane against the control plane, and 122 thereby localize faults. The second part suggests two methods of 123 reliable reply channels for the echo request message for more robust 124 fault isolation. 126 An important consideration in this design is that MPLS echo requests 127 follow the same data path that normal MPLS packets would traverse. 128 MPLS echo requests are meant primarily to validate the data plane, 129 and secondarily to verify the data plane against the control plane. 130 Mechanisms to check the control plane are valuable, but are not 131 covered in this document. 133 This document makes special use of the address range 127/8. This is 134 an exception to the behavior defined in RFC 1122 [RFC1122] and 135 updates that RFC. The motivation for this change and the details of 136 this exceptional use are discussed in section 2.1 below. 138 1.1. Conventions 140 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 141 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 142 document are to be interpreted as described in RFC 2119 [RFC2119]. 144 The term "Must Be Zero" (MBZ) is used in object descriptions for 145 reserved fields. These fields MUST be set to zero when sent and 146 ignored on receipt. 148 Terminology pertaining to L2 and L3 Virtual Private Networks (VPNs) 149 is defined in [RFC4026]. 151 Since this document refers to the MPLS Time to Live (TTL) far more 152 frequently than the IP TTL, the authors have chosen the convention of 153 using the unqualified "TTL" to mean "MPLS TTL" and using "IP TTL" for 154 the TTL value in the IP header. 156 1.2. Structure of This Document 158 The body of this memo contains four main parts: motivation, MPLS echo 159 request/reply packet format, LSP ping operation, and a reliable 160 return path. It is suggested that first-time readers skip the actual 161 packet formats and read the Theory of Operation first; the document 162 is structured the way it is to avoid forward references. 164 1.3. Contributors 166 A mechanism used to detect data plane failures in Multi-Protocol 167 Label Switching (MPLS) Label Switched Paths (LSPs) was originally 168 published as RFC 4379 in February 2006. It was produced by the MPLS 169 Working Group of the IETF and was jointly authored by Kireeti 170 Kompella and George Swallow. 172 The following made vital contributions to all aspects of the original 173 RFC 4379, and much of the material came out of debate and discussion 174 among this group. 176 Ronald P. Bonica, Juniper Networks, Inc. 177 Dave Cooper, Global Crossing 178 Ping Pan, Hammerhead Systems 179 Nischal Sheth, Juniper Networks, Inc. 180 Sanjay Wadhwa, Juniper Networks, Inc. 182 1.4. Scope of RFC4379bis work 184 The goal of this document is to take LSP Ping to an Internet 185 Standard. 187 [RFC4379] defines the basic mechanism for MPLS LSP validation that 188 can be used for fault detection and isolation. The scope of this 189 document also is to address various updates to MPLS LSP Ping, 190 including: 192 1. Updates to all references and citations. 194 1.5. ToDo 196 Please remove this ToDo prior to publication: 198 1. Incorporate Errata 199 2. Review IANA Allocations 201 2. Motivation 203 When an LSP fails to deliver user traffic, the failure cannot always 204 be detected by the MPLS control plane. There is a need to provide a 205 tool that would enable users to detect such traffic "black holes" or 206 misrouting within a reasonable period of time, and a mechanism to 207 isolate faults. 209 In this document, we describe a mechanism that accomplishes these 210 goals. This mechanism is modeled after the ping/traceroute paradigm: 211 ping (ICMP echo request [RFC0792]) is used for connectivity checks, 212 and traceroute is used for hop-by-hop fault localization as well as 213 path tracing. This document specifies a "ping" mode and a 214 "traceroute" mode for testing MPLS LSPs. 216 The basic idea is to verify that packets that belong to a particular 217 Forwarding Equivalence Class (FEC) actually end their MPLS path on a 218 Label Switching Router (LSR) that is an egress for that FEC. This 219 document proposes that this test be carried out by sending a packet 220 (called an "MPLS echo request") along the same data path as other 221 packets belonging to this FEC. An MPLS echo request also carries 222 information about the FEC whose MPLS path is being verified. This 223 echo request is forwarded just like any other packet belonging to 224 that FEC. In "ping" mode (basic connectivity check), the packet 225 should reach the end of the path, at which point it is sent to the 226 control plane of the egress LSR, which then verifies whether it is 227 indeed an egress for the FEC. In "traceroute" mode (fault 228 isolation), the packet is sent to the control plane of each transit 229 LSR, which performs various checks that it is indeed a transit LSR 230 for this path; this LSR also returns further information that helps 231 check the control plane against the data plane, i.e., that forwarding 232 matches what the routing protocols determined as the path. 234 One way these tools can be used is to periodically ping an FEC to 235 ensure connectivity. If the ping fails, one can then initiate a 236 traceroute to determine where the fault lies. One can also 237 periodically traceroute FECs to verify that forwarding matches the 238 control plane; however, this places a greater burden on transit LSRs 239 and thus should be used with caution. 241 2.1. Use of Address Range 127/8 243 As described above, LSP ping is intended as a diagnostic tool. It is 244 intended to enable providers of an MPLS-based service to isolate 245 network faults. In particular, LSP ping needs to diagnose situations 246 where the control and data planes are out of sync. It performs this 247 by routing an MPLS echo request packet based solely on its label 248 stack. That is, the IP destination address is never used in a 249 forwarding decision. In fact, the sender of an MPLS echo request 250 packet may not know, a priori, the address of the router at the end 251 of the LSP. 253 Providers of MPLS-based services also need the ability to trace all 254 of the possible paths that an LSP may take. Since most MPLS services 255 are based on IP unicast forwarding, these paths are subject to 256 equal-cost multi-path (ECMP) load sharing. 258 This leads to the following requirements: 260 1. Although the LSP in question may be broken in unknown ways, the 261 likelihood of a diagnostic packet being delivered to a user of an 262 MPLS service MUST be held to an absolute minimum. 264 2. If an LSP is broken in such a way that it prematurely terminates, 265 the diagnostic packet MUST NOT be IP forwarded. 267 3. A means of varying the diagnostic packets such that they exercise 268 all ECMP paths is thus REQUIRED. 270 Clearly, using general unicast addresses satisfies neither of the 271 first two requirements. A number of other options for addresses were 272 considered, including a portion of the private address space (as 273 determined by the network operator) and the newly designated IPv4 274 link local addresses. Use of the private address space was deemed 275 ineffective since the leading MPLS-based service is an IPv4 Virtual 276 Private Network (VPN). VPNs often use private addresses. 278 The IPv4 link local addresses are more attractive in that the scope 279 over which they can be forwarded is limited. However, if one were to 280 use an address from this range, it would still be possible for the 281 first recipient of a diagnostic packet that "escaped" from a broken 282 LSP to have that address assigned to the interface on which it 283 arrived and thus could mistakenly receive such a packet. 284 Furthermore, the IPv4 link local address range has only recently been 285 allocated. Many deployed routers would forward a packet with an 286 address from that range toward the default route. 288 The 127/8 range for IPv4 and that same range embedded in as 289 IPv4-mapped IPv6 addresses for IPv6 was chosen for a number of 290 reasons. 292 RFC 1122 allocates the 127/8 as "Internal host loopback address" and 293 states: "Addresses of this form MUST NOT appear outside a host." 294 Thus, the default behavior of hosts is to discard such packets. This 295 helps to ensure that if a diagnostic packet is misdirected to a host, 296 it will be silently discarded. 298 RFC 1812 [RFC1812] states: 300 A router SHOULD NOT forward, except over a loopback interface, any 301 packet that has a destination address on network 127. A router 302 MAY have a switch that allows the network manager to disable these 303 checks. If such a switch is provided, it MUST default to 304 performing the checks. 306 This helps to ensure that diagnostic packets are never IP forwarded. 308 The 127/8 address range provides 16M addresses allowing wide 309 flexibility in varying addresses to exercise ECMP paths. Finally, as 310 an implementation optimization, the 127/8 provides an easy means of 311 identifying possible LSP packets. 313 3. Packet Format 315 An MPLS echo request is a (possibly labeled) IPv4 or IPv6 UDP packet; 316 the contents of the UDP packet have the following format: 318 0 1 2 3 319 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 1 320 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 321 | Version Number | Global Flags | 322 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 323 | Message Type | Reply mode | Return Code | Return Subcode| 324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 325 | Sender's Handle | 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 | Sequence Number | 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 | TimeStamp Sent (seconds) | 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 | TimeStamp Sent (microseconds) | 332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 | TimeStamp Received (seconds) | 334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 | TimeStamp Received (microseconds) | 336 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 337 | TLVs ... | 338 . . 339 . . 340 . . 341 | | 342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 344 The Version Number is currently 1. (Note: the version number is to 345 be incremented whenever a change is made that affects the ability of 346 an implementation to correctly parse or process an MPLS echo 347 request/reply. These changes include any syntactic or semantic 348 changes made to any of the fixed fields, or to any Type-Length-Value 349 (TLV) or sub-TLV assignment or format that is defined at a certain 350 version number. The version number may not need to be changed if an 351 optional TLV or sub-TLV is added.) 353 The Global Flags field is a bit vector with the following format: 355 0 1 356 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 357 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 358 | MBZ |V| 359 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 361 One flag is defined for now, the V bit; the rest MUST be set to zero 362 when sending and ignored on receipt. 364 The V (Validate FEC Stack) flag is set to 1 if the sender wants the 365 receiver to perform FEC Stack validation; if V is 0, the choice is 366 left to the receiver. 368 The Message Type is one of the following: 370 Value Meaning 371 ----- ------- 372 1 MPLS echo request 373 2 MPLS echo reply 375 The Reply Mode can take one of the following values: 377 Value Meaning 378 ----- ------- 379 1 Do not reply 380 2 Reply via an IPv4/IPv6 UDP packet 381 3 Reply via an IPv4/IPv6 UDP packet with Router Alert 382 4 Reply via application level control channel 384 An MPLS echo request with 1 (Do not reply) in the Reply Mode field 385 may be used for one-way connectivity tests; the receiving router may 386 log gaps in the Sequence Numbers and/or maintain delay/jitter 387 statistics. An MPLS echo request would normally have 2 (Reply via an 388 IPv4/IPv6 UDP packet) in the Reply Mode field. If the normal IP 389 return path is deemed unreliable, one may use 3 (Reply via an IPv4/ 390 IPv6 UDP packet with Router Alert). Note that this requires that all 391 intermediate routers understand and know how to forward MPLS echo 392 replies. The echo reply uses the same IP version number as the 393 received echo request, i.e., an IPv4 encapsulated echo reply is sent 394 in response to an IPv4 encapsulated echo request. 396 Some applications support an IP control channel. One such example is 397 the associated control channel defined in Virtual Circuit 398 Connectivity Verification (VCCV) [RFC5085]. Any application that 399 supports an IP control channel between its control entities may set 400 the Reply Mode to 4 (Reply via application level control channel) to 401 ensure that replies use that same channel. Further definition of 402 this codepoint is application specific and thus beyond the scope of 403 this document. 405 Return Codes and Subcodes are described in the next section. 407 The Sender's Handle is filled in by the sender, and returned 408 unchanged by the receiver in the echo reply (if any). There are no 409 semantics associated with this handle, although a sender may find 410 this useful for matching up requests with replies. 412 The Sequence Number is assigned by the sender of the MPLS echo 413 request and can be (for example) used to detect missed replies. 415 The TimeStamp Sent is the time-of-day (in seconds and microseconds, 416 according to the sender's clock) in NTP format [RFC5905] when the 417 MPLS echo request is sent. The TimeStamp Received in an echo reply 418 is the time-of-day (according to the receiver's clock) in NTP format 419 that the corresponding echo request was received. 421 TLVs (Type-Length-Value tuples) have the following format: 423 0 1 2 3 424 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 1 425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 426 | Type | Length | 427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 428 | Value | 429 . . 430 . . 431 . . 432 | | 433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 435 Types are defined below; Length is the length of the Value field in 436 octets. The Value field depends on the Type; it is zero padded to 437 align to a 4-octet boundary. TLVs may be nested within other TLVs, 438 in which case the nested TLVs are called sub-TLVs. Sub-TLVs have 439 independent types and MUST also be 4-octet aligned. 441 Two examples follow. The Label Distribution Protocol (LDP) IPv4 FEC 442 sub-TLV has the following format: 444 0 1 2 3 445 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 1 446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 447 | Type = 1 (LDP IPv4 FEC) | Length = 5 | 448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 | IPv4 prefix | 450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 451 | Prefix Length | Must Be Zero | 452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 454 The Length for this TLV is 5. A Target FEC Stack TLV that contains 455 an LDP IPv4 FEC sub-TLV and a VPN IPv4 prefix sub-TLV has the 456 following format: 458 0 1 2 3 459 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 1 460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 461 | Type = 1 (FEC TLV) | Length = 12 | 462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 463 | sub-Type = 1 (LDP IPv4 FEC) | Length = 5 | 464 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 465 | IPv4 prefix | 466 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 467 | Prefix Length | Must Be Zero | 468 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 469 | sub-Type = 6 (VPN IPv4 prefix)| Length = 13 | 470 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 471 | Route Distinguisher | 472 | (8 octets) | 473 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 474 | IPv4 prefix | 475 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 476 | Prefix Length | Must Be Zero | 477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 479 A description of the Types and Values of the top-level TLVs for LSP 480 ping are given below: 482 Type # Value Field 483 ------ ----------- 484 1 Target FEC Stack 485 2 Downstream Mapping 486 3 Pad 487 4 Not Assigned 488 5 Vendor Enterprise Number 489 6 Not Assigned 490 7 Interface and Label Stack 491 8 Not Assigned 492 9 Errored TLVs 493 10 Reply TOS Byte 495 Types less than 32768 (i.e., with the high-order bit equal to 0) are 496 mandatory TLVs that MUST either be supported by an implementation or 497 result in the return code of 2 ("One or more of the TLVs was not 498 understood") being sent in the echo response. 500 Types greater than or equal to 32768 (i.e., with the high-order bit 501 equal to 1) are optional TLVs that SHOULD be ignored if the 502 implementation does not understand or support them. 504 3.1. Return Codes 506 The Return Code is set to zero by the sender. The receiver can set 507 it to one of the values listed below. The notation refers to 508 the Return Subcode. This field is filled in with the stack-depth for 509 those codes that specify that. For all other codes, the Return 510 Subcode MUST be set to zero. 512 Value Meaning 513 ----- ------- 514 0 No return code 515 1 Malformed echo request received 516 2 One or more of the TLVs was not understood 517 3 Replying router is an egress for the FEC at stack- 518 depth 519 4 Replying router has no mapping for the FEC at stack- 520 depth 521 5 Downstream Mapping Mismatch (See Note 1) 522 6 Upstream Interface Index Unknown (See Note 1) 523 7 Reserved 524 8 Label switched at stack-depth 525 9 Label switched but no MPLS forwarding at stack-depth 526 527 10 Mapping for this FEC is not the given label at stack- 528 depth 529 11 No label entry at stack-depth 530 12 Protocol not associated with interface at FEC stack- 531 depth 532 13 Premature termination of ping due to label stack 533 shrinking to a single label 535 Note 1 537 The Return Subcode contains the point in the label stack where 538 processing was terminated. If the RSC is 0, no labels were 539 processed. Otherwise the packet would have been label switched at 540 depth RSC. 542 3.2. Target FEC Stack 544 A Target FEC Stack is a list of sub-TLVs. The number of elements is 545 determined by looking at the sub-TLV length fields. 547 Sub-Type Length Value Field 548 -------- ------ ----------- 549 1 5 LDP IPv4 prefix 550 2 17 LDP IPv6 prefix 551 3 20 RSVP IPv4 LSP 552 4 56 RSVP IPv6 LSP 553 5 Not Assigned 554 6 13 VPN IPv4 prefix 555 7 25 VPN IPv6 prefix 556 8 14 L2 VPN endpoint 557 9 10 "FEC 128" Pseudowire (deprecated) 558 10 14 "FEC 128" Pseudowire 559 11 16+ "FEC 129" Pseudowire 560 12 5 BGP labeled IPv4 prefix 561 13 17 BGP labeled IPv6 prefix 562 14 5 Generic IPv4 prefix 563 15 17 Generic IPv6 prefix 564 16 4 Nil FEC 566 Other FEC Types will be defined as needed. 568 Note that this TLV defines a stack of FECs, the first FEC element 569 corresponding to the top of the label stack, etc. 571 An MPLS echo request MUST have a Target FEC Stack that describes the 572 FEC Stack being tested. For example, if an LSR X has an LDP mapping 573 [RFC5036] for 192.168.1.1 (say, label 1001), then to verify that 574 label 1001 does indeed reach an egress LSR that announced this prefix 575 via LDP, X can send an MPLS echo request with an FEC Stack TLV with 576 one FEC in it, namely, of type LDP IPv4 prefix, with prefix 577 192.168.1.1/32, and send the echo request with a label of 1001. 579 Say LSR X wanted to verify that a label stack of <1001, 23456> is the 580 right label stack to use to reach a VPN IPv4 prefix [see section 581 3.2.5] of 10/8 in VPN foo. Say further that LSR Y with loopback 582 address 192.168.1.1 announced prefix 10/8 with Route Distinguisher 583 RD-foo-Y (which may in general be different from the Route 584 Distinguisher that LSR X uses in its own advertisements for VPN foo), 585 label 23456 and BGP next hop 192.168.1.1 [RFC4271]. Finally, suppose 586 that LSR X receives a label binding of 1001 for 192.168.1.1 via LDP. 587 X has two choices in sending an MPLS echo request: X can send an MPLS 588 echo request with an FEC Stack TLV with a single FEC of type VPN IPv4 589 prefix with a prefix of 10/8 and a Route Distinguisher of RD-foo-Y. 590 Alternatively, X can send an FEC Stack TLV with two FECs, the first 591 of type LDP IPv4 with a prefix of 192.168.1.1/32 and the second of 592 type of IP VPN with a prefix 10/8 with Route Distinguisher of RD-foo- 593 Y. In either case, the MPLS echo request would have a label stack of 594 <1001, 23456>. (Note: in this example, 1001 is the "outer" label and 595 23456 is the "inner" label.) 597 3.2.1. LDP IPv4 Prefix 599 The IPv4 Prefix FEC is defined in [RFC5036]. When an LDP IPv4 prefix 600 is encoded in a label stack, the following format is used. The value 601 consists of 4 octets of an IPv4 prefix followed by 1 octet of prefix 602 length in bits; the format is given below. The IPv4 prefix is in 603 network byte order; if the prefix is shorter than 32 bits, trailing 604 bits SHOULD be set to zero. See [RFC5036] for an example of a 605 Mapping for an IPv4 FEC. 607 0 1 2 3 608 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 1 609 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 610 | IPv4 prefix | 611 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 612 | Prefix Length | Must Be Zero | 613 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 615 3.2.2. LDP IPv6 Prefix 617 The IPv6 Prefix FEC is defined in [RFC5036]. When an LDP IPv6 prefix 618 is encoded in a label stack, the following format is used. The value 619 consists of 16 octets of an IPv6 prefix followed by 1 octet of prefix 620 length in bits; the format is given below. The IPv6 prefix is in 621 network byte order; if the prefix is shorter than 128 bits, the 622 trailing bits SHOULD be set to zero. See [RFC5036] for an example of 623 a Mapping for an IPv6 FEC. 625 0 1 2 3 626 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 1 627 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 628 | IPv6 prefix | 629 | (16 octets) | 630 | | 631 | | 632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 633 | Prefix Length | Must Be Zero | 634 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 636 3.2.3. RSVP IPv4 LSP 638 The value has the format below. The value fields are taken from RFC 639 3209, sections 4.6.1.1 and 4.6.2.1. See [RFC3209]. 641 0 1 2 3 642 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 1 643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 644 | IPv4 tunnel end point address | 645 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 646 | Must Be Zero | Tunnel ID | 647 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 648 | Extended Tunnel ID | 649 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 650 | IPv4 tunnel sender address | 651 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 652 | Must Be Zero | LSP ID | 653 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 655 3.2.4. RSVP IPv6 LSP 657 The value has the format below. The value fields are taken from RFC 658 3209, sections 4.6.1.2 and 4.6.2.2. See [RFC3209]. 660 0 1 2 3 661 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 1 662 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 663 | IPv6 tunnel end point address | 664 | | 665 | | 666 | | 667 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 668 | Must Be Zero | Tunnel ID | 669 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 670 | Extended Tunnel ID | 671 | | 672 | | 673 | | 674 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 675 | IPv6 tunnel sender address | 676 | | 677 | | 678 | | 679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 680 | Must Be Zero | LSP ID | 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 683 3.2.5. VPN IPv4 Prefix 685 VPN-IPv4 Network Layer Routing Information (NLRI) is defined in 686 [RFC4365]. This document uses the term VPN IPv4 prefix for a VPN- 687 IPv4 NLRI that has been advertised with an MPLS label in BGP. See 688 [RFC3107]. 690 When a VPN IPv4 prefix is encoded in a label stack, the following 691 format is used. The value field consists of the Route Distinguisher 692 advertised with the VPN IPv4 prefix, the IPv4 prefix (with trailing 0 693 bits to make 32 bits in all), and a prefix length, as follows: 695 0 1 2 3 696 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 1 697 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 698 | Route Distinguisher | 699 | (8 octets) | 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 | IPv4 prefix | 702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 703 | Prefix Length | Must Be Zero | 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 706 The Route Distinguisher (RD) is an 8-octet identifier; it does not 707 contain any inherent information. The purpose of the RD is solely to 708 allow one to create distinct routes to a common IPv4 address prefix. 709 The encoding of the RD is not important here. When matching this 710 field to the local FEC information, it is treated as an opaque value. 712 3.2.6. VPN IPv6 Prefix 714 VPN-IPv6 Network Layer Routing Information (NLRI) is defined in 715 [RFC4365]. This document uses the term VPN IPv6 prefix for a VPN- 716 IPv6 NLRI that has been advertised with an MPLS label in BGP. See 717 [RFC3107]. 719 When a VPN IPv6 prefix is encoded in a label stack, the following 720 format is used. The value field consists of the Route Distinguisher 721 advertised with the VPN IPv6 prefix, the IPv6 prefix (with trailing 0 722 bits to make 128 bits in all), and a prefix length, as follows: 724 0 1 2 3 725 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 1 726 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 727 | Route Distinguisher | 728 | (8 octets) | 729 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 730 | IPv6 prefix | 731 | | 732 | | 733 | | 734 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 735 | Prefix Length | Must Be Zero | 736 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 738 The Route Distinguisher is identical to the VPN IPv4 Prefix RD, 739 except that it functions here to allow the creation of distinct 740 routes to IPv6 prefixes. See section 3.2.5. When matching this 741 field to local FEC information, it is treated as an opaque value. 743 3.2.7. L2 VPN Endpoint 745 VPLS stands for Virtual Private LAN Service. The terms VPLS BGP NLRI 746 and VE ID (VPLS Edge Identifier) are defined in [RFC4761]. This 747 document uses the simpler term L2 VPN endpoint when referring to a 748 VPLS BGP NLRI. The Route Distinguisher is an 8-octet identifier used 749 to distinguish information about various L2 VPNs advertised by a 750 node. The VE ID is a 2-octet identifier used to identify a 751 particular node that serves as the service attachment point within a 752 VPLS. The structure of these two identifiers is unimportant here; 753 when matching these fields to local FEC information, they are treated 754 as opaque values. The encapsulation type is identical to the PW Type 755 in section 3.2.8 below. 757 When an L2 VPN endpoint is encoded in a label stack, the following 758 format is used. The value field consists of a Route Distinguisher (8 759 octets), the sender (of the ping)'s VE ID (2 octets), the receiver's 760 VE ID (2 octets), and an encapsulation type (2 octets), formatted as 761 follows: 763 0 1 2 3 764 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 1 765 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 766 | Route Distinguisher | 767 | (8 octets) | 768 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 769 | Sender's VE ID | Receiver's VE ID | 770 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 771 | Encapsulation Type | Must Be Zero | 772 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 774 3.2.8. FEC 128 Pseudowire (Deprecated) 776 FEC 128 (0x80) is defined in [RFC4447], as are the terms PW ID 777 (Pseudowire ID) and PW Type (Pseudowire Type). A PW ID is a non-zero 778 32-bit connection ID. The PW Type is a 15-bit number indicating the 779 encapsulation type. It is carried right justified in the field below 780 termed encapsulation type with the high-order bit set to zero. Both 781 of these fields are treated in this protocol as opaque values. 783 When an FEC 128 is encoded in a label stack, the following format is 784 used. The value field consists of the remote PE address (the 785 destination address of the targeted LDP session), the PW ID, and the 786 encapsulation type as follows: 788 0 1 2 3 789 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 1 790 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 791 | Remote PE Address | 792 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 793 | PW ID | 794 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 795 | PW Type | Must Be Zero | 796 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 798 This FEC is deprecated and is retained only for backward 799 compatibility. Implementations of LSP ping SHOULD accept and process 800 this TLV, but SHOULD send LSP ping echo requests with the new TLV 801 (see next section), unless explicitly configured to use the old TLV. 803 An LSR receiving this TLV SHOULD use the source IP address of the LSP 804 echo request to infer the sender's PE address. 806 3.2.9. FEC 128 Pseudowire (Current) 808 FEC 128 (0x80) is defined in [RFC4447], as are the terms PW ID 809 (Pseudowire ID) and PW Type (Pseudowire Type). A PW ID is a non-zero 810 32-bit connection ID. The PW Type is a 15-bit number indicating the 811 encapsulation type. It is carried right justified in the field below 812 termed encapsulation type with the high-order bit set to zero. 814 Both of these fields are treated in this protocol as opaque values. 815 When matching these field to the local FEC information, the match 816 MUST be exact. 818 When an FEC 128 is encoded in a label stack, the following format is 819 used. The value field consists of the sender's PE address (the 820 source address of the targeted LDP session), the remote PE address 821 (the destination address of the targeted LDP session), the PW ID, and 822 the encapsulation type as follows: 824 0 1 2 3 825 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 1 826 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 827 | Sender's PE Address | 828 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 829 | Remote PE Address | 830 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 831 | PW ID | 832 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 833 | PW Type | Must Be Zero | 834 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 836 3.2.10. FEC 129 Pseudowire 838 FEC 129 (0x81) and the terms PW Type, Attachment Group Identifier 839 (AGI), Attachment Group Identifier Type (AGI Type), Attachment 840 Individual Identifier Type (AII Type), Source Attachment Individual 841 Identifier (SAII), and Target Attachment Individual Identifier (TAII) 842 are defined in [RFC4447]. The PW Type is a 15-bit number indicating 843 the encapsulation type. It is carried right justified in the field 844 below PW Type with the high-order bit set to zero. All the other 845 fields are treated as opaque values and copied directly from the FEC 846 129 format. All of these values together uniquely define the FEC 847 within the scope of the LDP session identified by the source and 848 remote PE addresses. 850 When an FEC 129 is encoded in a label stack, the following format is 851 used. The Length of this TLV is 16 + AGI length + SAII length + TAII 852 length. Padding is used to make the total length a multiple of 4; 853 the length of the padding is not included in the Length field. 855 0 1 2 3 856 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 1 857 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 858 | Sender's PE Address | 859 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 860 | Remote PE Address | 861 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 862 | PW Type | AGI Type | AGI Length | 863 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 864 ~ AGI Value ~ 865 | | 866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 867 | AII Type | SAII Length | SAII Value | 868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 869 ~ SAII Value (continued) ~ 870 | | 871 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 872 | AII Type | TAII Length | TAII Value | 873 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 874 ~ TAII Value (continued) ~ 875 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 876 | TAII (cont.) | 0-3 octets of zero padding | 877 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 879 3.2.11. BGP Labeled IPv4 Prefix 881 BGP labeled IPv4 prefixes are defined in [RFC3107]. When a BGP 882 labeled IPv4 prefix is encoded in a label stack, the following format 883 is used. The value field consists the IPv4 prefix (with trailing 0 884 bits to make 32 bits in all), and the prefix length, as follows: 886 0 1 2 3 887 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 1 888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 889 | IPv4 Prefix | 890 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 891 | Prefix Length | Must Be Zero | 892 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 894 3.2.12. BGP Labeled IPv6 Prefix 896 BGP labeled IPv6 prefixes are defined in [RFC3107]. When a BGP 897 labeled IPv6 prefix is encoded in a label stack, the following format 898 is used. The value consists of 16 octets of an IPv6 prefix followed 899 by 1 octet of prefix length in bits; the format is given below. The 900 IPv6 prefix is in network byte order; if the prefix is shorter than 901 128 bits, the trailing bits SHOULD be set to zero. 903 0 1 2 3 904 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 1 905 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 906 | IPv6 prefix | 907 | (16 octets) | 908 | | 909 | | 910 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 911 | Prefix Length | Must Be Zero | 912 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 914 3.2.13. Generic IPv4 Prefix 916 The value consists of 4 octets of an IPv4 prefix followed by 1 octet 917 of prefix length in bits; the format is given below. The IPv4 prefix 918 is in network byte order; if the prefix is shorter than 32 bits, 919 trailing bits SHOULD be set to zero. This FEC is used if the 920 protocol advertising the label is unknown or may change during the 921 course of the LSP. An example is an inter-AS LSP that may be 922 signaled by LDP in one Autonomous System (AS), by RSVP-TE [RFC3209] 923 in another AS, and by BGP between the ASes, such as is common for 924 inter-AS VPNs. 926 0 1 2 3 927 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 1 928 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 929 | IPv4 prefix | 930 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 931 | Prefix Length | Must Be Zero | 932 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 934 3.2.14. Generic IPv6 Prefix 936 The value consists of 16 octets of an IPv6 prefix followed by 1 octet 937 of prefix length in bits; the format is given below. The IPv6 prefix 938 is in network byte order; if the prefix is shorter than 128 bits, the 939 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 3.2.15. Nil FEC 954 At times, labels from the reserved range, e.g., Router Alert and 955 Explicit-null, may be added to the label stack for various diagnostic 956 purposes such as influencing load-balancing. These labels may have 957 no explicit FEC associated with them. The Nil FEC Stack is defined 958 to allow a Target FEC Stack sub-TLV to be added to the Target FEC 959 Stack to account for such labels so that proper validation can still 960 be performed. 962 The Length is 4. Labels are 20-bit values treated as numbers. 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 | Label | MBZ | 968 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 970 Label is the actual label value inserted in the label stack; the MBZ 971 fields MUST be zero when sent and ignored on receipt. 973 3.3. Downstream Mapping 975 The Downstream Mapping object is a TLV that MAY be included in an 976 echo request message. Only one Downstream Mapping object may appear 977 in an echo request. The presence of a Downstream Mapping object is a 978 request that Downstream Mapping objects be included in the echo 979 reply. If the replying router is the destination of the FEC, then a 980 Downstream Mapping TLV SHOULD NOT be included in the echo reply. 981 Otherwise the replying router SHOULD include a Downstream Mapping 982 object for each interface over which this FEC could be forwarded. 983 For a more precise definition of the notion of "downstream", see 984 section 3.3.2, "Downstream Router and Interface". 986 The Length is K + M + 4*N octets, where M is the Multipath Length, 987 and N is the number of Downstream Labels. Values for K are found in 988 the description of Address Type below. The Value field of a 989 Downstream Mapping has the following format: 991 0 1 2 3 992 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 1 993 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 994 | MTU | Address Type | DS Flags | 995 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 996 | Downstream IP Address (4 or 16 octets) | 997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 998 | Downstream Interface Address (4 or 16 octets) | 999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1000 | Multipath Type| Depth Limit | Multipath Length | 1001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1002 . . 1003 . (Multipath Information) . 1004 . . 1005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1006 | Downstream Label | Protocol | 1007 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1008 . . 1009 . . 1010 . . 1011 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1012 | Downstream Label | Protocol | 1013 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1015 Maximum Transmission Unit (MTU) 1017 The MTU is the size in octets of the largest MPLS frame (including 1018 label stack) that fits on the interface to the Downstream LSR. 1020 Address Type 1022 The Address Type indicates if the interface is numbered or 1023 unnumbered. It also determines the length of the Downstream IP 1024 Address and Downstream Interface fields. The resulting total for 1025 the initial part of the TLV is listed in the table below as "K 1026 Octets". The Address Type is set to one of the following values: 1028 Type # Address Type K Octets 1029 ------ ------------ -------- 1030 1 IPv4 Numbered 16 1031 2 IPv4 Unnumbered 16 1032 3 IPv6 Numbered 40 1033 4 IPv6 Unnumbered 28 1035 DS Flags 1037 The DS Flags field is a bit vector with the following format: 1039 0 1 2 3 4 5 6 7 1040 +-+-+-+-+-+-+-+-+ 1041 | Rsvd(MBZ) |I|N| 1042 +-+-+-+-+-+-+-+-+ 1044 Two flags are defined currently, I and N. The remaining flags MUST 1045 be set to zero when sending and ignored on receipt. 1047 Flag Name and Meaning 1048 ---- ---------------- 1049 I Interface and Label Stack Object Request 1051 When this flag is set, it indicates that the replying 1052 router SHOULD include an Interface and Label Stack 1053 Object in the echo reply message. 1055 N Treat as a Non-IP Packet 1057 Echo request messages will be used to diagnose non-IP 1058 flows. However, these messages are carried in IP 1059 packets. For a router that alters its ECMP algorithm 1060 based on the FEC or deep packet examination, this flag 1061 requests that the router treat this as it would if the 1062 determination of an IP payload had failed. 1064 Downstream IP Address and Downstream Interface Address 1066 IPv4 addresses and interface indices are encoded in 4 octets; IPv6 1067 addresses are encoded in 16 octets. 1069 If the interface to the downstream LSR is numbered, then the 1070 Address Type MUST be set to IPv4 or IPv6, the Downstream IP 1071 Address MUST be set to either the downstream LSR's Router ID or 1072 the interface address of the downstream LSR, and the Downstream 1073 Interface Address MUST be set to the downstream LSR's interface 1074 address. 1076 If the interface to the downstream LSR is unnumbered, the Address 1077 Type MUST be IPv4 Unnumbered or IPv6 Unnumbered, the Downstream IP 1078 Address MUST be the downstream LSR's Router ID, and the Downstream 1079 Interface Address MUST be set to the index assigned by the 1080 upstream LSR to the interface. 1082 If an LSR does not know the IP address of its neighbor, then it 1083 MUST set the Address Type to either IPv4 Unnumbered or IPv6 1084 Unnumbered. For IPv4, it must set the Downstream IP Address to 1085 127.0.0.1; for IPv6 the address is set to 0::1. In both cases, 1086 the interface index MUST be set to 0. If an LSR receives an Echo 1087 Request packet with either of these addresses in the Downstream IP 1088 Address field, this indicates that it MUST bypass interface 1089 verification but continue with label validation. 1091 If the originator of an Echo Request packet wishes to obtain 1092 Downstream Mapping information but does not know the expected 1093 label stack, then it SHOULD set the Address Type to either IPv4 1094 Unnumbered or IPv6 Unnumbered. For IPv4, it MUST set the 1095 Downstream IP Address to 224.0.0.2; for IPv6 the address MUST be 1096 set to FF02::2. In both cases, the interface index MUST be set to 1097 0. If an LSR receives an Echo Request packet with the all-routers 1098 multicast address, then this indicates that it MUST bypass both 1099 interface and label stack validation, but return Downstream 1100 Mapping TLVs using the information provided. 1102 Multipath Type 1104 The following Multipath Types are defined: 1106 Key Type Multipath Information 1107 --- ---------------- --------------------- 1108 0 no multipath Empty (Multipath Length = 0) 1109 2 IP address IP addresses 1110 4 IP address range low/high address pairs 1111 8 Bit-masked IP IP address prefix and bit mask 1112 address set 1113 9 Bit-masked label set Label prefix and bit mask 1115 Type 0 indicates that all packets will be forwarded out this one 1116 interface. 1118 Types 2, 4, 8, and 9 specify that the supplied Multipath Information 1119 will serve to exercise this path. 1121 Depth Limit 1123 The Depth Limit is applicable only to a label stack and is the 1124 maximum number of labels considered in the hash; this SHOULD be 1125 set to zero if unspecified or unlimited. 1127 Multipath Length 1129 The length in octets of the Multipath Information. 1131 Multipath Information 1133 Address or label values encoded according to the Multipath Type. 1134 See the next section below for encoding details. 1136 Downstream Label(s) 1138 The set of labels in the label stack as it would have appeared if 1139 this router were forwarding the packet through this interface. 1140 Any Implicit Null labels are explicitly included. Labels are 1141 treated as numbers, i.e., they are right justified in the field. 1143 A Downstream Label is 24 bits, in the same format as an MPLS label 1144 minus the TTL field, i.e., the MSBit of the label is bit 0, the 1145 LSBit is bit 19, the EXP bits are bits 20-22, and bit 23 is the S 1146 bit. The replying router SHOULD fill in the EXP and S bits; the 1147 LSR receiving the echo reply MAY choose to ignore these bits. 1148 Protocol 1150 The Protocol is taken from the following table: 1152 Protocol # Signaling Protocol 1153 ---------- ------------------ 1154 0 Unknown 1155 1 Static 1156 2 BGP 1157 3 LDP 1158 4 RSVP-TE 1160 3.3.1. Multipath Information Encoding 1162 The Multipath Information encodes labels or addresses that will 1163 exercise this path. The Multipath Information depends on the 1164 Multipath Type. The contents of the field are shown in the table 1165 above. IPv4 addresses are drawn from the range 127/8; IPv6 addresses 1166 are drawn from the range 0:0:0:0:0:FFFF:127/104. Labels are treated 1167 as numbers, i.e., they are right justified in the field. For Type 4, 1168 ranges indicated by Address pairs MUST NOT overlap and MUST be in 1169 ascending sequence. 1171 Type 8 allows a more dense encoding of IP addresses. The IP prefix 1172 is formatted as a base IP address with the non-prefix low-order bits 1173 set to zero. The maximum prefix length is 27. Following the prefix 1174 is a mask of length 2^(32-prefix length) bits for IPv4 and 1175 2^(128-prefix length) bits for IPv6. Each bit set to 1 represents a 1176 valid address. The address is the base IPv4 address plus the 1177 position of the bit in the mask where the bits are numbered left to 1178 right beginning with zero. For example, the IPv4 addresses 1179 127.2.1.0, 127.2.1.5-127.2.1.15, and 127.2.1.20-127.2.1.29 would be 1180 encoded as follows: 1182 0 1 2 3 1183 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 1184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1185 |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| 1186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1187 |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| 1188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1190 Those same addresses embedded in IPv6 would be encoded as follows: 1192 0 1 2 3 1193 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 1194 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1195 |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| 1196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1197 |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| 1198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1199 |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| 1200 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1201 |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| 1202 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1203 |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| 1204 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1205 |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| 1206 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1208 Type 9 allows a more dense encoding of labels. The label prefix is 1209 formatted as a base label value with the non-prefix low-order bits 1210 set to zero. The maximum prefix (including leading zeros due to 1211 encoding) length is 27. Following the prefix is a mask of length 1212 2^(32-prefix length) bits. Each bit set to one represents a valid 1213 label. The label is the base label plus the position of the bit in 1214 the mask where the bits are numbered left to right beginning with 1215 zero. Label values of all the odd numbers between 1152 and 1279 1216 would be encoded as follows: 1218 0 1 2 3 1219 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 1220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1221 |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| 1222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1223 |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| 1224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1225 |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| 1226 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1227 |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| 1228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1229 |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| 1230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1232 If the received Multipath Information is non-null, the labels and IP 1233 addresses MUST be picked from the set provided. If none of these 1234 labels or addresses map to a particular downstream interface, then 1235 for that interface, the type MUST be set to 0. If the received 1236 Multipath Information is null (i.e., Multipath Length = 0, or for 1237 Types 8 and 9, a mask of all zeros), the type MUST be set to 0. 1239 For example, suppose LSR X at hop 10 has two downstream LSRs, Y and 1240 Z, for the FEC in question. The received X could return Multipath 1241 Type 4, with low/high IP addresses of 127.1.1.1->127.1.1.255 for 1242 downstream LSR Y and 127.2.1.1->127.2.1.255 for downstream LSR Z. 1243 The head end reflects this information to LSR Y. Y, which has three 1244 downstream LSRs, U, V, and W, computes that 127.1.1.1->127.1.1.127 1245 would go to U and 127.1.1.128-> 127.1.1.255 would go to V. Y would 1246 then respond with 3 Downstream Mappings: to U, with Multipath Type 4 1247 (127.1.1.1->127.1.1.127); to V, with Multipath Type 4 1248 (127.1.1.127->127.1.1.255); and to W, with Multipath Type 0. 1250 Note that computing Multipath Information may impose a significant 1251 processing burden on the receiver. A receiver MAY thus choose to 1252 process a subset of the received prefixes. The sender, on receiving 1253 a reply to a Downstream Mapping with partial information, SHOULD 1254 assume that the prefixes missing in the reply were skipped by the 1255 receiver, and MAY re-request information about them in a new echo 1256 request. 1258 3.3.2. Downstream Router and Interface 1260 The notion of "downstream router" and "downstream interface" should 1261 be explained. Consider an LSR X. If a packet that was originated 1262 with TTL n>1 arrived with outermost label L and TTL=1 at LSR X, X 1263 must be able to compute which LSRs could receive the packet if it was 1264 originated with TTL=n+1, over which interface the request would 1265 arrive and what label stack those LSRs would see. (It is outside the 1266 scope of this document to specify how this computation is done.) The 1267 set of these LSRs/interfaces consists of the downstream routers/ 1268 interfaces (and their corresponding labels) for X with respect to L. 1269 Each pair of downstream router and interface requires a separate 1270 Downstream Mapping to be added to the reply. 1272 The case where X is the LSR originating the echo request is a special 1273 case. X needs to figure out what LSRs would receive the MPLS echo 1274 request for a given FEC Stack that X originates with TTL=1. 1276 The set of downstream routers at X may be alternative paths (see the 1277 discussion below on ECMP) or simultaneous paths (e.g., for MPLS 1278 multicast). In the former case, the Multipath Information is used as 1279 a hint to the sender as to how it may influence the choice of these 1280 alternatives. 1282 3.4. Pad TLV 1284 The value part of the Pad TLV contains a variable number (>= 1) of 1285 octets. The first octet takes values from the following table; all 1286 the other octets (if any) are ignored. The receiver SHOULD verify 1287 that the TLV is received in its entirety, but otherwise ignores the 1288 contents of this TLV, apart from the first octet. 1290 Value Meaning 1291 ----- ------- 1292 1 Drop Pad TLV from reply 1293 2 Copy Pad TLV to reply 1294 3-255 Reserved for future use 1296 3.5. Vendor Enterprise Number 1298 SMI Private Enterprise Numbers are maintained by IANA. The Length is 1299 always 4; the value is the SMI Private Enterprise code, in network 1300 octet order, of the vendor with a Vendor Private extension to any of 1301 the fields in the fixed part of the message, in which case this TLV 1302 MUST be present. If none of the fields in the fixed part of the 1303 message have Vendor Private extensions, inclusion of this TLV is 1304 OPTIONAL. Vendor Private ranges for Message Types, Reply Modes, and 1305 Return Codes have been defined. When any of these are used, the 1306 Vendor Enterprise Number TLV MUST be included in the message. 1308 3.6. Interface and Label Stack 1310 The Interface and Label Stack TLV MAY be included in a reply message 1311 to report the interface on which the request message was received and 1312 the label stack that was on the packet when it was received. Only 1313 one such object may appear. The purpose of the object is to allow 1314 the upstream router to obtain the exact interface and label stack 1315 information as it appears at the replying LSR. 1317 The Length is K + 4*N octets; N is the number of labels in the label 1318 stack. Values for K are found in the description of Address Type 1319 below. The Value field of a Downstream Mapping has the following 1320 format: 1322 0 1 2 3 1323 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 1324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1325 | Address Type | Must Be Zero | 1326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1327 | IP Address (4 or 16 octets) | 1328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1329 | Interface (4 or 16 octets) | 1330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1331 . . 1332 . . 1333 . Label Stack . 1334 . . 1335 . . 1336 . . 1337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1339 Address Type 1341 The Address Type indicates if the interface is numbered or 1342 unnumbered. It also determines the length of the IP Address and 1343 Interface fields. The resulting total for the initial part of the 1344 TLV is listed in the table below as "K Octets". The Address Type 1345 is set to one of the following values: 1347 Type # Address Type K Octets 1348 ------ ------------ -------- 1349 1 IPv4 Numbered 12 1350 2 IPv4 Unnumbered 12 1351 3 IPv6 Numbered 36 1352 4 IPv6 Unnumbered 24 1354 IP Address and Interface 1356 IPv4 addresses and interface indices are encoded in 4 octets; IPv6 1357 addresses are encoded in 16 octets. 1359 If the interface upon which the echo request message was received 1360 is numbered, then the Address Type MUST be set to IPv4 or IPv6, 1361 the IP Address MUST be set to either the LSR's Router ID or the 1362 interface address, and the Interface MUST be set to the interface 1363 address. 1365 If the interface is unnumbered, the Address Type MUST be either 1366 IPv4 Unnumbered or IPv6 Unnumbered, the IP Address MUST be the 1367 LSR's Router ID, and the Interface MUST be set to the index 1368 assigned to the interface. 1370 Label Stack 1372 The label stack of the received echo request message. If any TTL 1373 values have been changed by this router, they SHOULD be restored. 1375 3.7. Errored TLVs 1377 The following TLV is a TLV that MAY be included in an echo reply to 1378 inform the sender of an echo request of mandatory TLVs either not 1379 supported by an implementation or parsed and found to be in error. 1381 The Value field contains the TLVs that were not understood, encoded 1382 as sub-TLVs. 1384 0 1 2 3 1385 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 1386 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1387 | Type = 9 | Length | 1388 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1389 | Value | 1390 . . 1391 . . 1392 . . 1393 | | 1394 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1396 3.8. Reply TOS Byte TLV 1398 This TLV MAY be used by the originator of the echo request to request 1399 that an echo reply be sent with the IP header TOS byte set to the 1400 value specified in the TLV. This TLV has a length of 4 with the 1401 following value field. 1403 0 1 2 3 1404 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 1405 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1406 | Reply-TOS Byte| Must Be Zero | 1407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1409 4. Theory of Operation 1411 An MPLS echo request is used to test a particular LSP. The LSP to be 1412 tested is identified by the "FEC Stack"; for example, if the LSP was 1413 set up via LDP, and is to an egress IP address of 10.1.1.1, the FEC 1414 Stack contains a single element, namely, an LDP IPv4 prefix sub-TLV 1415 with value 10.1.1.1/32. If the LSP being tested is an RSVP LSP, the 1416 FEC Stack consists of a single element that captures the RSVP Session 1417 and Sender Template that uniquely identifies the LSP. 1419 FEC Stacks can be more complex. For example, one may wish to test a 1420 VPN IPv4 prefix of 10.1/8 that is tunneled over an LDP LSP with 1421 egress 10.10.1.1. The FEC Stack would then contain two sub-TLVs, the 1422 bottom being a VPN IPv4 prefix, and the top being an LDP IPv4 prefix. 1423 If the underlying (LDP) tunnel were not known, or was considered 1424 irrelevant, the FEC Stack could be a single element with just the VPN 1425 IPv4 sub-TLV. 1427 When an MPLS echo request is received, the receiver is expected to 1428 verify that the control plane and data plane are both healthy (for 1429 the FEC Stack being pinged) and that the two planes are in sync. The 1430 procedures for this are in section 4.4 below. 1432 4.1. Dealing with Equal-Cost Multi-Path (ECMP) 1434 LSPs need not be simple point-to-point tunnels. Frequently, a single 1435 LSP may originate at several ingresses, and terminate at several 1436 egresses; this is very common with LDP LSPs. LSPs for a given FEC 1437 may also have multiple "next hops" at transit LSRs. At an ingress, 1438 there may also be several different LSPs to choose from to get to the 1439 desired endpoint. Finally, LSPs may have backup paths, detour paths, 1440 and other alternative paths to take should the primary LSP go down. 1442 To deal with the last two first: it is assumed that the LSR sourcing 1443 MPLS echo requests can force the echo request into any desired LSP, 1444 so choosing among multiple LSPs at the ingress is not an issue. The 1445 problem of probing the various flavors of backup paths that will 1446 typically not be used for forwarding data unless the primary LSP is 1447 down will not be addressed here. 1449 Since the actual LSP and path that a given packet may take may not be 1450 known a priori, it is useful if MPLS echo requests can exercise all 1451 possible paths. This, although desirable, may not be practical, 1452 because the algorithms that a given LSR uses to distribute packets 1453 over alternative paths may be proprietary. 1455 To achieve some degree of coverage of alternate paths, there is a 1456 certain latitude in choosing the destination IP address and source 1457 UDP port for an MPLS echo request. This is clearly not sufficient; 1458 in the case of traceroute, more latitude is offered by means of the 1459 Multipath Information of the Downstream Mapping TLV. This is used as 1460 follows. An ingress LSR periodically sends an MPLS traceroute 1461 message to determine whether there are multipaths for a given LSP. 1462 If so, each hop will provide some information how each of its 1463 downstream paths can be exercised. The ingress can then send MPLS 1464 echo requests that exercise these paths. If several transit LSRs 1465 have ECMP, the ingress may attempt to compose these to exercise all 1466 possible paths. However, full coverage may not be possible. 1468 4.2. Testing LSPs That Are Used to Carry MPLS Payloads 1470 To detect certain LSP breakages, it may be necessary to encapsulate 1471 an MPLS echo request packet with at least one additional label when 1472 testing LSPs that are used to carry MPLS payloads (such as LSPs used 1473 to carry L2VPN and L3VPN traffic. For example, when testing LDP or 1474 RSVP-TE LSPs, just sending an MPLS echo request packet may not detect 1475 instances where the router immediately upstream of the destination of 1476 the LSP ping may forward the MPLS echo request successfully over an 1477 interface not configured to carry MPLS payloads because of the use of 1478 penultimate hop popping. Since the receiving router has no means to 1479 differentiate whether the IP packet was sent unlabeled or implicitly 1480 labeled, the addition of labels shimmed above the MPLS echo request 1481 (using the Nil FEC) will prevent a router from forwarding such a 1482 packet out unlabeled interfaces. 1484 4.3. Sending an MPLS Echo Request 1486 An MPLS echo request is a UDP packet. The IP header is set as 1487 follows: the source IP address is a routable address of the sender; 1488 the destination IP address is a (randomly chosen) IPv4 address from 1489 the range 127/8 or IPv6 address from the range 1490 0:0:0:0:0:FFFF:127/104. The IP TTL is set to 1. The source UDP port 1491 is chosen by the sender; the destination UDP port is set to 3503 1492 (assigned by IANA for MPLS echo requests). The Router Alert option 1493 MUST be set in the IP header. 1495 An MPLS echo request is sent with a label stack corresponding to the 1496 FEC Stack being tested. Note that further labels could be applied 1497 if, for example, the normal route to the topmost FEC in the stack is 1498 via a Traffic Engineered Tunnel [RFC3209]. If all of the FECs in the 1499 stack correspond to Implicit Null labels, the MPLS echo request is 1500 considered unlabeled even if further labels will be applied in 1501 sending the packet. 1503 If the echo request is labeled, one MAY (depending on what is being 1504 pinged) set the TTL of the innermost label to 1, to prevent the ping 1505 request going farther than it should. Examples of where this SHOULD 1506 be done include pinging a VPN IPv4 or IPv6 prefix, an L2 VPN endpoint 1507 or a pseudowire. Preventing the ping request from going too far can 1508 also be accomplished by inserting a Router Alert label above this 1509 label; however, this may lead to the undesired side effect that MPLS 1510 echo requests take a different data path than actual data. For more 1511 information on how these mechanisms can be used for pseudowire 1512 connectivity verification, see [RFC5085]. 1514 In "ping" mode (end-to-end connectivity check), the TTL in the 1515 outermost label is set to 255. In "traceroute" mode (fault isolation 1516 mode), the TTL is set successively to 1, 2, and so on. 1518 The sender chooses a Sender's Handle and a Sequence Number. When 1519 sending subsequent MPLS echo requests, the sender SHOULD increment 1520 the Sequence Number by 1. However, a sender MAY choose to send a 1521 group of echo requests with the same Sequence Number to improve the 1522 chance of arrival of at least one packet with that Sequence Number. 1524 The TimeStamp Sent is set to the time-of-day (in seconds and 1525 microseconds) that the echo request is sent. The TimeStamp Received 1526 is set to zero. 1528 An MPLS echo request MUST have an FEC Stack TLV. Also, the Reply 1529 Mode must be set to the desired reply mode; the Return Code and 1530 Subcode are set to zero. In the "traceroute" mode, the echo request 1531 SHOULD include a Downstream Mapping TLV. 1533 4.4. Receiving an MPLS Echo Request 1535 Sending an MPLS echo request to the control plane is triggered by one 1536 of the following packet processing exceptions: Router Alert option, 1537 IP TTL expiration, MPLS TTL expiration, MPLS Router Alert label, or 1538 the destination address in the 127/8 address range. The control 1539 plane further identifies it by UDP destination port 3503. 1541 For reporting purposes the bottom of stack is considered to be stack- 1542 depth of 1. This is to establish an absolute reference for the case 1543 where the actual stack may have more labels than there are FECs in 1544 the Target FEC Stack. 1546 Furthermore, in all the error codes listed in this document, a stack- 1547 depth of 0 means "no value specified". This allows compatibility 1548 with existing implementations that do not use the Return Subcode 1549 field. 1551 An LSR X that receives an MPLS echo request then processes it as 1552 follows. 1554 1. General packet sanity is verified. If the packet is not well- 1555 formed, LSR X SHOULD send an MPLS Echo Reply with the Return Code 1556 set to "Malformed echo request received" and the Subcode to zero. 1557 If there are any TLVs not marked as "Ignore" that LSR X does not 1558 understand, LSR X SHOULD send an MPLS "TLV not understood" (as 1559 appropriate), and the Subcode set to zero. In the latter case, 1560 the misunderstood TLVs (only) are included as sub-TLVs in an 1561 Errored TLVs TLV in the reply. The header fields Sender's 1562 Handle, Sequence Number, and Timestamp Sent are not examined, but 1563 are included in the MPLS echo reply message. 1565 The algorithm uses the following variables and identifiers: 1567 Interface-I: the interface on which the MPLS echo request was 1568 received. 1570 Stack-R: the label stack on the packet as it was received. 1572 Stack-D: the label stack carried in the Downstream Mapping 1573 TLV (not always present) 1575 Label-L: the label from the actual stack currently being 1576 examined. Requires no initialization. 1578 Label-stack-depth: the depth of label being verified. Initialized 1579 to the number of labels in the received label 1580 stack S. 1582 FEC-stack-depth: depth of the FEC in the Target FEC Stack that 1583 should be used to verify the current actual 1584 label. Requires no initialization. 1586 Best-return-code: contains the return code for the echo reply 1587 packet as currently best known. As algorithm 1588 progresses, this code may change depending on the 1589 results of further checks that it performs. 1591 Best-rtn-subcode: similar to Best-return-code, but for the Echo 1592 Reply Subcode. 1594 FEC-status: result value returned by the FEC Checking 1595 algorithm described in section 4.4.1. 1597 /* Save receive context information */ 1599 2. If the echo request is good, LSR X stores the interface over 1600 which the echo was received in Interface-I, and the label stack 1601 with which it came in Stack-R. 1603 /* The rest of the algorithm iterates over the labels in Stack-R, 1604 verifies validity of label values, reports associated label switching 1605 operations (for traceroute), verifies correspondence between the 1606 Stack-R and the Target FEC Stack description in the body of the echo 1607 request, and reports any errors. */ 1609 /* The algorithm iterates as follows. */ 1611 3. Label Validation: 1613 If Label-stack-depth is 0 { 1615 /* The LSR needs to report its being a tail-end for the LSP */ 1617 Set FEC-stack-depth to 1, set Label-L to 3 (Implicit Null). 1618 Set Best-return-code to 3 ("Replying router is an egress for 1619 the FEC at stack depth"), set Best-rtn-subcode to the value of 1620 FEC-stack-depth (1) and go to step 5 (Egress Processing). 1622 } 1624 /* This step assumes there is always an entry for well-known label 1625 values */ 1627 Set Label-L to the value extracted from Stack-R at depth Label- 1628 stack-depth. Look up Label-L in the Incoming Label Map (ILM) to 1629 determine if the label has been allocated and an operation is 1630 associated with it. 1632 If there is no entry for L { 1634 /* Indicates a temporary or permanent label synchronization 1635 problem the LSR needs to report an error */ 1637 Set Best-return-code to 11 ("No label entry at stack-depth") 1638 and Best-rtn-subcode to Label-stack-depth. Go to step 7 (Send 1639 Reply Packet). 1641 } 1643 Else { 1645 Retrieve the associated label operation from the corresponding 1646 NLFE and proceed to step 4 (Label Operation check). 1648 } 1650 4. Label Operation Check 1651 If the label operation is "Pop and Continue Processing" { 1653 /* Includes Explicit Null and Router Alert label cases */ 1655 Iterate to the next label by decrementing Label-stack-depth and 1656 loop back to step 3 (Label Validation). 1658 } 1660 If the label operation is "Swap or Pop and Switch based on Popped 1661 Label" { 1663 Set Best-return-code to 8 ("Label switched at stack-depth") and 1664 Best-rtn-subcode to Label-stack-depth to report transit 1665 switching. 1667 If a Downstream Mapping TLV is present in the received echo 1668 request { 1670 If the IP address in the TLV is 127.0.0.1 or 0::1 { 1672 Set Best-return-code to 6 ("Upstream Interface Index 1673 Unknown"). An Interface and Label Stack TLV SHOULD be 1674 included in the reply and filled with Interface-I and 1675 Stack-R. 1677 } 1679 Else { 1681 Verify that the IP address, interface address, and label 1682 stack in the Downstream Mapping TLV match Interface-I and 1683 Stack-R. If there is a mismatch, set Best-return-code to 1684 5, "Downstream Mapping Mismatch". An Interface and Label 1685 Stack TLV SHOULD be included in the reply and filled in 1686 based on Interface-I and Stack-R. Go to step 7 (Send 1687 Reply Packet). 1689 } 1691 } 1693 For each available downstream ECMP path { 1695 Retrieve output interface from the NHLFE entry. 1697 /* Note: this return code is set even if Label-stack-depth 1698 is one */ 1699 If the output interface is not MPLS enabled { 1701 Set Best-return-code to Return Code 9, "Label switched 1702 but no MPLS forwarding at stack-depth" and set Best-rtn- 1703 subcode to Label-stack-depth and goto Send_Reply_Packet. 1705 } 1707 If a Downstream Mapping TLV is present { 1709 A Downstream Mapping TLV SHOULD be included in the echo 1710 reply (see section 3.3) filled in with information about 1711 the current ECMP path. 1713 } 1715 } 1717 If no Downstream Mapping TLV is present, or the Downstream IP 1718 Address is set to the ALLROUTERS multicast address, go to step 1719 7 (Send Reply Packet). 1721 If the "Validate FEC Stack" flag is not set and the LSR is not 1722 configured to perform FEC checking by default, go to step 7 1723 (Send Reply Packet). 1725 /* Validate the Target FEC Stack in the received echo request. 1727 First determine FEC-stack-depth from the Downstream Mapping 1728 TLV. This is done by walking through Stack-D (the Downstream 1729 labels) from the bottom, decrementing the number of labels for 1730 each non-Implicit Null label, while incrementing FEC-stack- 1731 depth for each label. If the Downstream Mapping TLV contains 1732 one or more Implicit Null labels, FEC-stack-depth may be 1733 greater than Label-stack-depth. To be consistent with the 1734 above stack-depths, the bottom is considered to entry 1. 1735 */ 1737 Set FEC-stack-depth to 0. Set i to Label-stack-depth. 1739 While (i > 0 ) do { 1741 ++FEC-stack-depth. 1742 if Stack-D[FEC-stack-depth] != 3 (Implicit Null) 1743 --i. 1744 } 1745 If the number of labels in the FEC stack is greater than or 1746 equal to FEC-stack-depth { 1747 Perform the FEC Checking procedure (see subsection 4.4.1 1748 below). 1750 If FEC-status is 2, set Best-return-code to 10 ("Mapping for 1751 this FEC is not the given label at stack-depth"). 1753 If the return code is 1, set Best-return-code to FEC-return- 1754 code and Best-rtn-subcode to FEC-stack-depth. 1755 } 1757 Go to step 7 (Send Reply Packet). 1758 } 1760 5. Egress Processing: 1762 /* These steps are performed by the LSR that identified itself as 1763 the tail-end LSR for an LSP. */ 1765 If received echo request contains no Downstream Mapping TLV, or 1766 the Downstream IP Address is set to 127.0.0.1 or 0::1 go to step 6 1767 (Egress FEC Validation). 1769 Verify that the IP address, interface address, and label stack in 1770 the Downstream Mapping TLV match Interface-I and Stack-R. If not, 1771 set Best-return-code to 5, "Downstream Mapping Mis-match". A 1772 Received Interface and Label Stack TLV SHOULD be created for the 1773 echo response packet. Go to step 7 (Send Reply Packet). 1775 6. Egress FEC Validation: 1777 /* This is a loop for all entries in the Target FEC Stack starting 1778 with FEC-stack-depth. */ 1780 Perform FEC checking by following the algorithm described in 1781 subsection 4.4.1 for Label-L and the FEC at FEC-stack-depth. 1783 Set Best-return-code to FEC-code and Best-rtn-subcode to the value 1784 in FEC-stack-depth. 1786 If FEC-status (the result of the check) is 1, 1787 go to step 7 (Send Reply Packet). 1789 /* Iterate to the next FEC entry */ 1790 ++FEC-stack-depth. 1791 If FEC-stack-depth > the number of FECs in the FEC-stack, 1792 go to step 7 (Send Reply Packet). 1794 If FEC-status is 0 { 1796 ++Label-stack-depth. 1797 If Label-stack-depth > the number of labels in Stack-R, 1798 Go to step 7 (Send Reply Packet). 1800 Label-L = extracted label from Stack-R at depth 1801 Label-stack-depth. 1802 Loop back to step 6 (Egress FEC Validation). 1803 } 1805 7. Send Reply Packet: 1807 Send an MPLS echo reply with a Return Code of Best-return-code, 1808 and a Return Subcode of Best-rtn-subcode. Include any TLVs 1809 created during the above process. The procedures for sending the 1810 echo reply are found in subsection 4.4.1. 1812 4.4.1. FEC Validation 1814 /* This subsection describes validation of an FEC entry within the 1815 Target FEC Stack and accepts an FEC, Label-L, and Interface-I. The 1816 algorithm performs the following steps. */ 1818 1. Two return values, FEC-status and FEC-return-code, are 1819 initialized to 0. 1821 2. If the FEC is the Nil FEC { 1823 If Label-L is either Explicit_Null or Router_Alert, return. 1825 Else { 1827 Set FEC-return-code to 10 ("Mapping for this FEC is not the 1828 given label at stack-depth"). 1829 Set FEC-status to 1 1830 Return. 1831 } 1833 } 1835 3. Check the FEC label mapping that describes how traffic received 1836 on the LSP is further switched or which application it is 1837 associated with. If no mapping exists, set FEC-return-code to 1838 Return 4, "Replying router has no mapping for the FEC at stack- 1839 depth". Set FEC-status to 1. Return. 1841 4. If the label mapping for FEC is Implicit Null, set FEC-status to 1842 2 and proceed to step 5. Otherwise, if the label mapping for FEC 1843 is Label-L, proceed to step 5. Otherwise, set FEC-return-code to 1844 10 ("Mapping for this FEC is not the given label at stack- 1845 depth"), set FEC-status to 1, and return. 1847 5. This is a protocol check. Check what protocol would be used to 1848 advertise FEC. If it can be determined that no protocol 1849 associated with Interface-I would have advertised an FEC of that 1850 FEC-Type, set FEC-return-code to 12 ("Protocol not associated 1851 with interface at FEC stack-depth"). Set FEC-status to 1. 1853 6. Return. 1855 4.5. Sending an MPLS Echo Reply 1857 An MPLS echo reply is a UDP packet. It MUST ONLY be sent in response 1858 to an MPLS echo request. The source IP address is a routable address 1859 of the replier; the source port is the well-known UDP port for LSP 1860 ping. The destination IP address and UDP port are copied from the 1861 source IP address and UDP port of the echo request. The IP TTL is 1862 set to 255. If the Reply Mode in the echo request is "Reply via an 1863 IPv4 UDP packet with Router Alert", then the IP header MUST contain 1864 the Router Alert IP option. If the reply is sent over an LSP, the 1865 topmost label MUST in this case be the Router Alert label (1) (see 1866 [RFC3032]). 1868 The format of the echo reply is the same as the echo request. The 1869 Sender's Handle, the Sequence Number, and TimeStamp Sent are copied 1870 from the echo request; the TimeStamp Received is set to the time-of- 1871 day that the echo request is received (note that this information is 1872 most useful if the time-of-day clocks on the requester and the 1873 replier are synchronized). The FEC Stack TLV from the echo request 1874 MAY be copied to the reply. 1876 The replier MUST fill in the Return Code and Subcode, as determined 1877 in the previous subsection. 1879 If the echo request contains a Pad TLV, the replier MUST interpret 1880 the first octet for instructions regarding how to reply. 1882 If the replying router is the destination of the FEC, then Downstream 1883 Mapping TLVs SHOULD NOT be included in the echo reply. 1885 If the echo request contains a Downstream Mapping TLV, and the 1886 replying router is not the destination of the FEC, the replier SHOULD 1887 compute its downstream routers and corresponding labels for the 1888 incoming label, and add Downstream Mapping TLVs for each one to the 1889 echo reply it sends back. 1891 If the Downstream Mapping TLV contains Multipath Information 1892 requiring more processing than the receiving router is willing to 1893 perform, the responding router MAY choose to respond with only a 1894 subset of multipaths contained in the echo request Downstream 1895 Mapping. (Note: The originator of the echo request MAY send another 1896 echo request with the Multipath Information that was not included in 1897 the reply.) 1899 Except in the case of Reply Mode 4, "Reply via application level 1900 control channel", echo replies are always sent in the context of the 1901 IP/MPLS network. 1903 4.6. Receiving an MPLS Echo Reply 1905 An LSR X should only receive an MPLS echo reply in response to an 1906 MPLS echo request that it sent. Thus, on receipt of an MPLS echo 1907 reply, X should parse the packet to ensure that it is well-formed, 1908 then attempt to match up the echo reply with an echo request that it 1909 had previously sent, using the destination UDP port and the Sender's 1910 Handle. If no match is found, then X jettisons the echo reply; 1911 otherwise, it checks the Sequence Number to see if it matches. 1913 If the echo reply contains Downstream Mappings, and X wishes to 1914 traceroute further, it SHOULD copy the Downstream Mapping(s) into its 1915 next echo request(s) (with TTL incremented by one). 1917 4.7. Issue with VPN IPv4 and IPv6 Prefixes 1919 Typically, an LSP ping for a VPN IPv4 prefix or VPN IPv6 prefix is 1920 sent with a label stack of depth greater than 1, with the innermost 1921 label having a TTL of 1. This is to terminate the ping at the egress 1922 PE, before it gets sent to the customer device. However, under 1923 certain circumstances, the label stack can shrink to a single label 1924 before the ping hits the egress PE; this will result in the ping 1925 terminating prematurely. One such scenario is a multi-AS Carrier's 1926 Carrier VPN. 1928 To get around this problem, one approach is for the LSR that receives 1929 such a ping to realize that the ping terminated prematurely, and send 1930 back error code 13. In that case, the initiating LSR can retry the 1931 ping after incrementing the TTL on the VPN label. In this fashion, 1932 the ingress LSR will sequentially try TTL values until it finds one 1933 that allows the VPN ping to reach the egress PE. 1935 4.8. Non-compliant Routers 1937 If the egress for the FEC Stack being pinged does not support MPLS 1938 ping, then no reply will be sent, resulting in possible "false 1939 negatives". If in "traceroute" mode, a transit LSR does not support 1940 LSP ping, then no reply will be forthcoming from that LSR for some 1941 TTL, say, n. The LSR originating the echo request SHOULD try sending 1942 the echo request with TTL=n+1, n+2, ..., n+k to probe LSRs further 1943 down the path. In such a case, the echo request for TTL > n SHOULD 1944 be sent with Downstream Mapping TLV "Downstream IP Address" field set 1945 to the ALLROUTERs multicast address until a reply is received with a 1946 Downstream Mapping TLV. The label stack MAY be omitted from the 1947 Downstream Mapping TLV. Furthermore, the "Validate FEC Stack" flag 1948 SHOULD NOT be set until an echo reply packet with a Downstream 1949 Mapping TLV is received. 1951 5. Security Considerations 1953 Overall, the security needs for LSP ping are similar to those of ICMP 1954 ping. 1956 There are at least three approaches to attacking LSRs using the 1957 mechanisms defined here. One is a Denial-of-Service attack, by 1958 sending MPLS echo requests/replies to LSRs and thereby increasing 1959 their workload. The second is obfuscating the state of the MPLS data 1960 plane liveness by spoofing, hijacking, replaying, or otherwise 1961 tampering with MPLS echo requests and replies. The third is an 1962 unauthorized source using an LSP ping to obtain information about the 1963 network. To avoid potential Denial-of-Service attacks, it is 1964 RECOMMENDED that implementations regulate the LSP ping traffic going 1965 to the control plane. A rate limiter SHOULD be applied to the well- 1966 known UDP port defined below. 1968 Unsophisticated replay and spoofing attacks involving faking or 1969 replaying MPLS echo reply messages are unlikely to be effective. 1970 These replies would have to match the Sender's Handle and Sequence 1971 Number of an outstanding MPLS echo request message. A non-matching 1972 replay would be discarded as the sequence has moved on, thus a spoof 1973 has only a small window of opportunity. However, to provide a 1974 stronger defense, an implementation MAY also validate the TimeStamp 1975 Sent by requiring and exact match on this field. 1977 To protect against unauthorized sources using MPLS echo request 1978 messages to obtain network information, it is RECOMMENDED that 1979 implementations provide a means of checking the source addresses of 1980 MPLS echo request messages against an access list before accepting 1981 the message. 1983 It is not clear how to prevent hijacking (non-delivery) of echo 1984 requests or replies; however, if these messages are indeed hijacked, 1985 LSP ping will report that the data plane is not working as it should. 1987 It does not seem vital (at this point) to secure the data carried in 1988 MPLS echo requests and replies, although knowledge of the state of 1989 the MPLS data plane may be considered confidential by some. 1990 Implementations SHOULD, however, provide a means of filtering the 1991 addresses to which echo reply messages may be sent. 1993 Although this document makes special use of 127/8 address, these are 1994 used only in conjunction with the UDP port 3503. Furthermore, these 1995 packets are only processed by routers. All other hosts MUST treat 1996 all packets with a destination address in the range 127/8 in 1997 accordance to RFC 1122. Any packet received by a router with a 1998 destination address in the range 127/8 without a destination UDP port 1999 of 3503 MUST be treated in accordance to RFC 1812. In particular, 2000 the default behavior is to treat packets destined to a 127/8 address 2001 as "martians". 2003 6. IANA Considerations 2005 The TCP and UDP port number 3503 has been allocated by IANA for LSP 2006 echo requests and replies. 2008 The following sections detail the new name spaces to be managed by 2009 IANA. For each of these name spaces, the space is divided into 2010 assignment ranges; the following terms are used in describing the 2011 procedures by which IANA allocates values: "Standards Action" (as 2012 defined in [RFC5226]), "Specification Required", and "Vendor Private 2013 Use". 2015 Values from "Specification Required" ranges MUST be registered with 2016 IANA. The request MUST be made via an Experimental RFC that 2017 describes the format and procedures for using the code point; the 2018 actual assignment is made during the IANA actions for the RFC. 2020 Values from "Vendor Private" ranges MUST NOT be registered with IANA; 2021 however, the message MUST contain an enterprise code as registered 2022 with the IANA SMI Private Network Management Private Enterprise 2023 Numbers. For each name space that has a Vendor Private range, it 2024 must be specified where exactly the SMI Private Enterprise Number 2025 resides; see below for examples. In this way, several enterprises 2026 (vendors) can use the same code point without fear of collision. 2028 6.1. Message Types, Reply Modes, Return Codes 2030 The IANA has created and will maintain registries for Message Types, 2031 Reply Modes, and Return Codes. Each of these can take values in the 2032 range 0-255. Assignments in the range 0-191 are via Standards 2033 Action; assignments in the range 192-251 are made via "Specification 2034 Required"; values in the range 252-255 are for Vendor Private Use, 2035 and MUST NOT be allocated. 2037 If any of these fields fall in the Vendor Private range, a top-level 2038 Vendor Enterprise Number TLV MUST be present in the message. 2040 Message Types defined in this document are the following: 2042 Value Meaning 2043 ----- ------- 2044 1 MPLS echo request 2045 2 MPLS echo reply 2047 Reply Modes defined in this document are the following: 2049 Value Meaning 2050 ----- ------- 2051 1 Do not reply 2052 2 Reply via an IPv4/IPv6 UDP packet 2053 3 Reply via an IPv4/IPv6 UDP packet with Router Alert 2054 4 Reply via application level control channel 2056 Return Codes defined in this document are listed in section 3.1. 2058 6.2. TLVs 2060 The IANA has created and will maintain a registry for the Type field 2061 of top-level TLVs as well as for any associated sub-TLVs. Note the 2062 meaning of a sub-TLV is scoped by the TLV. The number spaces for the 2063 sub-TLVs of various TLVs are independent. 2065 The valid range for TLVs and sub-TLVs is 0-65535. Assignments in the 2066 range 0-16383 and 32768-49161 are made via Standards Action as 2067 defined in [RFC5226]; assignments in the range 16384-31743 and 2068 49162-64511 are made via "Specification Required" as defined above; 2069 values in the range 31744-32767 and 64512-65535 are for Vendor 2070 Private Use, and MUST NOT be allocated. 2072 If a TLV or sub-TLV has a Type that falls in the range for Vendor 2073 Private Use, the Length MUST be at least 4, and the first four octets 2074 MUST be that vendor's SMI Private Enterprise Number, in network octet 2075 order. The rest of the Value field is private to the vendor. TLVs 2076 and sub-TLVs defined in this document are the following: 2078 Type Sub-Type Value Field 2079 ---- -------- ----------- 2080 1 Target FEC Stack 2081 1 LDP IPv4 prefix 2082 2 LDP IPv6 prefix 2083 3 RSVP IPv4 LSP 2084 4 RSVP IPv6 LSP 2085 5 Not Assigned 2086 6 VPN IPv4 prefix 2087 7 VPN IPv6 prefix 2088 8 L2 VPN endpoint 2089 9 "FEC 128" Pseudowire (Deprecated) 2090 10 "FEC 128" Pseudowire 2091 11 "FEC 129" Pseudowire 2092 12 BGP labeled IPv4 prefix 2093 13 BGP labeled IPv6 prefix 2094 14 Generic IPv4 prefix 2095 15 Generic IPv6 prefix 2096 16 Nil FEC 2097 2 Downstream Mapping 2098 3 Pad 2099 4 Not Assigned 2100 5 Vendor Enterprise Number 2101 6 Not Assigned 2102 7 Interface and Label Stack 2103 8 Not Assigned 2104 9 Errored TLVs 2105 Any value The TLV not understood 2106 10 Reply TOS Byte 2108 7. Acknowledgements 2110 The original acknowledgements from RFC 4379 state the following: 2112 This document is the outcome of many discussions among many 2113 people, including Manoj Leelanivas, Paul Traina, Yakov Rekhter, 2114 Der-Hwa Gan, Brook Bailey, Eric Rosen, Ina Minei, Shivani 2115 Aggarwal, and Vanson Lim. 2117 The description of the Multipath Information sub-field of the 2118 Downstream Mapping TLV was adapted from text suggested by Curtis 2119 Villamizar. 2121 We would like to thank Loa Andersson for motivating the advancement 2122 of this bis specification. 2124 8. References 2126 8.1. Normative References 2128 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 2129 Communication Layers", STD 3, RFC 1122, DOI 10.17487/ 2130 RFC1122, October 1989, 2131 . 2133 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 2134 RFC 1812, DOI 10.17487/RFC1812, June 1995, 2135 . 2137 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2138 Requirement Levels", BCP 14, RFC 2119, March 1997. 2140 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., 2141 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack 2142 Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, 2143 . 2145 [RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual 2146 Private Network (VPN) Terminology", RFC 4026, DOI 2147 10.17487/RFC4026, March 2005, 2148 . 2150 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 2151 Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 2152 10.17487/RFC4271, January 2006, 2153 . 2155 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 2156 Label Switched (MPLS) Data Plane Failures", RFC 4379, 2157 February 2006. 2159 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 2160 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 2161 DOI 10.17487/RFC5226, May 2008, 2162 . 2164 [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, 2165 "Network Time Protocol Version 4: Protocol and Algorithms 2166 Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, 2167 . 2169 8.2. Informative References 2171 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 2172 RFC 792, September 1981. 2174 [RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in 2175 BGP-4", RFC 3107, DOI 10.17487/RFC3107, May 2001, 2176 . 2178 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 2179 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 2180 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 2181 . 2183 [RFC4365] Rosen, E., "Applicability Statement for BGP/MPLS IP 2184 Virtual Private Networks (VPNs)", RFC 4365, DOI 10.17487/ 2185 RFC4365, February 2006, 2186 . 2188 [RFC4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and 2189 G. Heron, "Pseudowire Setup and Maintenance Using the 2190 Label Distribution Protocol (LDP)", RFC 4447, DOI 2191 10.17487/RFC4447, April 2006, 2192 . 2194 [RFC4761] Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private 2195 LAN Service (VPLS) Using BGP for Auto-Discovery and 2196 Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007, 2197 . 2199 [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., 2200 "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, 2201 October 2007, . 2203 [RFC5085] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit 2204 Connectivity Verification (VCCV): A Control Channel for 2205 Pseudowires", RFC 5085, December 2007. 2207 Authors' Addresses 2209 Carlos Pignataro 2210 Cisco Systems, Inc. 2212 Email: cpignata@cisco.com 2213 Nagendra Kumar 2214 Cisco Systems, Inc. 2216 Email: naikumar@cisco.com 2218 Sam Aldrin 2219 Google 2221 Email: aldrin.ietf@gmail.com 2223 Mach(Guoyi) Chen 2224 Huawei 2226 Email: mach.chen@huawei.com