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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group K. Kompella (Juniper) 3 Internet Draft P. Pan (Ciena) 4 draft-ietf-mpls-lsp-ping-03.txt N. Sheth (Juniper) 5 Category: Standards Track D. Cooper (Global Crossing) 6 Expires: December 2003 G. Swallow (Cisco) 7 S. Wadhwa (Juniper) 8 R. Bonica (WorldCom) 9 June 2003 11 Detecting MPLS Data Plane Failures 13 *** DRAFT *** 15 Status of this Memo 17 This document is an Internet-Draft and is in full conformance with 18 all provisions of Section 10 of RFC2026. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF), its areas, and its working groups. Note that 22 other groups may also distribute working documents as Internet- 23 Drafts. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as ``work in progress.'' 30 The list of current Internet-Drafts can be accessed at 31 http://www.ietf.org/ietf/1id-abstracts.txt 33 The list of Internet-Draft Shadow Directories can be accessed at 34 http://www.ietf.org/shadow.html. 36 Copyright Notice 38 Copyright (C) The Internet Society (2003). All Rights Reserved. 40 Abstract 42 This document describes a simple and efficient mechanism that can be 43 used to detect data plane failures in Multi-Protocol Label Switching 44 (MPLS) Label Switched Paths (LSPs). There are two parts to this 45 document: information carried in an MPLS "echo request" and "echo 46 reply" for the purposes of fault detection and isolation; and 47 mechanisms for reliably sending the echo reply. 49 Changes since last revision 51 (This section to be removed before publication.) 53 - Changed title to "Detecting MPLS Data Plane Failures" 54 - removed section 5 "Reliable Reply Path" 55 - filled in IANA section 56 - added new top level TLV for Vendor Enterprise Code 57 - Clarified Downstream Router ID and Downstream Interface Address 58 - Clarified receiving procedure 59 - Example for multipath operation 61 Issues 63 (This section to be removed before publication.) 65 - Question: use two bits from the TLV space to indicate 66 - Ignore TLV if not understood 67 - Reflect TLV in reply 68 - Tweak error codes? Add stack depth? 69 - More multipath stuff? 71 1. Introduction 73 This document describes a simple and efficient mechanism that can be 74 used to detect data plane failures in MPLS LSPs. There are two parts 75 to this document: information carried in an MPLS "echo request" and 76 "echo reply"; and mechanisms for transporting the echo reply. The 77 first part aims at providing enough information to check correct 78 operation of the data plane, as well as a mechanism to verify the 79 data plane against the control plane, and thereby localize faults. 80 The second part suggests two methods of reliable reply channels for 81 the echo request message, for more robust fault isolation. 83 An important consideration in this design is that MPLS echo requests 84 follow the same data path that normal MPLS packets would traverse. 85 MPLS echo requests are meant primarily to validate the data plane, 86 and secondarily to verify the data plane against the control plane. 87 Mechanisms to check the control plane are valuable, but are not 88 covered in this document. 90 To avoid potential Denial of Service attacks, it is recommended to 91 regulate the MPLS ping traffic going to the control plane. A rate 92 limiter should be applied to the well-known UDP port defined below. 94 1.1. Conventions 96 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 97 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 98 document are to be interpreted as described in RFC 2119 [KEYWORDS]. 100 1.2. Structure of this document 102 The body of this memo contains four main parts: motivation, MPLS echo 103 request/reply packet format, MPLS ping operation, and a reliable 104 return path. It is suggested that first-time readers skip the actual 105 packet formats and read the Theory of Operation first; the document 106 is structured the way it is to avoid forward references. 108 The last section (reliable return path for RSVP LSPs) may be removed 109 in a future revision. 111 2. Motivation 113 When an LSP fails to deliver user traffic, the failure cannot always 114 be detected by the MPLS control plane. There is a need to provide a 115 tool that would enable users to detect such traffic "black holes" or 116 misrouting within a reasonable period of time; and a mechanism to 117 isolate faults. 119 In this document, we describe a mechanism that accomplishes these 120 goals. This mechanism is modeled after the ping/traceroute paradigm: 121 ping (ICMP echo request [ICMP]) is used for connectivity checks, and 122 traceroute is used for hop-by-hop fault localization as well as path 123 tracing. This document specifies a "ping mode" and a "traceroute" 124 mode for testing MPLS LSPs. 126 The basic idea is to test that packets that belong to a particular 127 Forwarding Equivalence Class (FEC) actually end their MPLS path on an 128 LSR that is an egress for that FEC. This document proposes that this 129 test be carried out by sending a packet (called an "MPLS echo 130 request") along the same data path as other packets belonging to this 131 FEC. An MPLS echo request also carries information about the FEC 132 whose MPLS path is being verified. This echo request is forwarded 133 just like any other packet belonging to that FEC. In "ping" mode 134 (basic connectivity check), the packet should reach the end of the 135 path, at which point it is sent to the control plane of the egress 136 LSR, which then verifies that it is indeed an egress for the FEC. In 137 "traceroute" mode (fault isolation), the packet is sent to the 138 control plane of each transit LSR, which performs various checks that 139 it is indeed a transit LSR for this path; this LSR also returns 140 further information that helps check the control plane against the 141 data plane, i.e., that forwarding matches what the routing protocols 142 determined as the path. 144 One way these tools can be used is to periodically ping a FEC to 145 ensure connectivity. If the ping fails, one can then initiate a 146 traceroute to determine where the fault lies. One can also 147 periodically traceroute FECs to verify that forwarding matches the 148 control plane; however, this places a greater burden on transit LSRs 149 and thus should be used with caution. 151 3. Packet Format 153 An MPLS echo request is a (possibly labelled) UDP packet; the 154 contents of the UDP packet have the following format: 156 0 1 2 3 157 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 1 158 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 159 | Version Number | Must Be Zero | 160 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 161 | Message Type | Reply mode | Return Code | Return Subcode| 162 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 163 | Sender's Handle | 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 165 | Sequence Number | 166 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 167 | TimeStamp Sent (seconds) | 168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 169 | TimeStamp Sent (microseconds) | 170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 171 | TimeStamp Received (seconds) | 172 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 173 | TimeStamp Received (microseconds) | 174 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 175 | TLVs ... | 176 . . 177 . . 178 . . 179 | | 180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 182 The Version Number is currently 1. (Note: the Version Number is to 183 be incremented whenever a change is made that affects the ability of 184 an implementation to correctly parse or process an MPLS echo 185 request/reply. These changes include any syntactic or semantic 186 changes made to any of the fixed fields, or to any TLV or sub-TLV 187 assignment or format that is defined at a certain version number. 188 The Version Number may not need to be changed if an optional TLV or 189 sub-TLV is added.) 191 The Message Type is one of the following: 193 Value Meaning 194 ----- ------- 195 1 MPLS Echo Request 196 2 MPLS Echo Reply 198 The Reply Mode can take one of the following values: 200 Value Meaning 201 ----- ------- 202 1 Do not reply 203 2 Reply via an IPv4 UDP packet 204 3 Reply via an IPv4 UDP packet with Router Alert 206 An MPLS echo request with "Do not reply" may be used for one-way 207 connectivity tests; the receiving router may log gaps in the sequence 208 numbers and/or maintain delay/jitter statistics. An MPLS echo 209 request would normally have "Reply via an IPv4 UDP packet"; if the 210 normal IPv4 return path is deemed unreliable, one may use "Reply via 211 an IPv4 UDP packet with Router Alert" (note that this requires that 212 all intermediate routers understand and know how to forward MPLS echo 213 replies). 215 The Return Code is set to zero by the sender. The receiver can set 216 it to one of the following values: 218 Value Meaning 219 ----- ------- 220 0 The error code is contained in the Error Code TLV 221 1 Malformed echo request received 222 2 One or more of the TLVs was not understood 223 3 Replying router is an egress for the FEC 224 4 Replying router has no mapping for the FEC 225 5 Replying router is not one of the "Downstream Routers" 226 6 Replying router is one of the "Downstream Routers", 227 and its mapping for this FEC on the received interface 228 is the given label 229 7 Replying router is one of the "Downstream Routers", 230 but its mapping for this FEC is not the given label 232 The Return Subcode is unused at present and SHOULD be set to zero. 234 The Sender's Handle is filled in by the sender, and returned 235 unchanged by the receiver in the echo reply (if any). There are no 236 semantics associated with this handle, although a sender may find 237 this useful for matching up requests with replies. 239 The Sequence Number is assigned by the sender of the MPLS echo 240 request, and can be (for example) used to detect missed replies. 242 The TimeStamp Sent is the time-of-day (in seconds and microseconds, 243 wrt the sender's clock) when the MPLS echo request is sent. The 244 TimeStamp Received in an echo reply is the time-of-day (wrt the 245 receiver's clock) that the corresponding echo request was received. 247 TLVs (Type-Length-Value tuples) have the following format: 249 0 1 2 3 250 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 1 251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 252 | Type | Length | 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 254 | Value | 255 . . 256 . . 257 . . 258 | | 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 261 Types are defined below; Length is the length of the Value field in 262 octets. The Value field depends on the Type; it is zero padded to 263 align to a four-octet boundary. 265 Type # Value Field 266 ------ ----------- 267 1 Target FEC Stack 268 2 Downstream Mapping 269 3 Pad 270 4 Error Code 271 5 Vendor Enterprise Code 273 3.1. Target FEC Stack 275 A Target FEC Stack is a list of sub-TLVs. The number of elements is 276 determined by the looking at the sub-TLV length fields. 278 Sub-Type # Length Value Field 279 ---------- ------ ----------- 280 1 5 LDP IPv4 prefix 281 2 17 LDP IPv6 prefix 282 3 20 RSVP IPv4 Session Query 283 4 56 RSVP IPv6 Session Query 284 5 Reserved; see Appendix 285 6 13 VPN IPv4 prefix 286 7 25 VPN IPv6 prefix 287 8 14 L2 VPN endpoint 288 9 10 L2 circuit ID 290 Other FEC Types will be defined as needed. 292 Note that this TLV defines a stack of FECs, the first FEC element 293 corresponding to the top of the label stack, etc. 295 An MPLS echo request MUST have a Target FEC Stack that describes the 296 FEC stack being tested. For example, if an LSR X has an LDP mapping 297 for 192.168.1.1 (say label 1001), then to verify that label 1001 does 298 indeed reach an egress LSR that announced this prefix via LDP, X can 299 send an MPLS echo request with a FEC Stack TLV with one FEC in it, 300 namely of type LDP IPv4 prefix, with prefix 192.168.1.1/32, and send 301 the echo request with a label of 1001. 303 Say LSR X wanted to verify that a label stack of <1001, 23456> is the 304 right label stack to use to reach a VPN IPv4 prefix of 10/8 in VPN 305 foo. Say further that LSR Y with loopback address 192.168.1.1 306 announced prefix 10/8 with Route Distinguisher RD-foo-Y (which may in 307 general be different from the Route Distinguisher that LSR X uses in 308 its own advertisements for VPN foo), label 23456 and BGP nexthop 309 192.168.1.1. Finally, suppose that LSR X receives a label binding of 310 1001 for 192.168.1.1 via LDP. X has two choices in sending an MPLS 311 echo request: X can send an MPLS echo request with a FEC Stack TLV 312 with a single FEC of type VPN IPv4 prefix with a prefix of 10/8 and a 313 Route Distinguisher of RD-foo-Y. Alternatively, X can send a FEC 314 Stack TLV with two FECs, the first of type LDP IPv4 with a prefix of 315 192.168.1.1/32 and the second of type of IP VPN with a prefix 10/8 316 with Route Distinguisher of RD-foo-Y. In either case, the MPLS echo 317 request would have a label stack of <1001, 23456>. (Note: in this 318 example, 1001 is the "outer" label and 23456 is the "inner" label.) 320 3.1.1. LDP IPv4 Prefix 322 The value consists of four octets of an IPv4 prefix followed by one 323 octet of prefix length in bits. The IPv4 prefix is in network byte 324 order. See [LDP] for an example of a Mapping for an IPv4 FEC. 326 3.1.2. LDP IPv6 Prefix 328 The value consists of sixteen octets of an IPv6 prefix followed by 329 one octet of prefix length in bits. The IPv6 prefix is in network 330 byte order. See [LDP] for an example of a Mapping for an IPv6 FEC. 332 3.1.3. RSVP IPv4 Session 334 The value has the format below. The value fields are taken from 335 [RFC3209, sections 4.6.1.1 and 4.6.2.1]. 337 0 1 2 3 338 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 1 339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 340 | IPv4 tunnel end point address | 341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 342 | Must Be Zero | Tunnel ID | 343 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 344 | Extended Tunnel ID | 345 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 346 | IPv4 tunnel sender address | 347 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 348 | Must Be Zero | LSP ID | 349 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 351 3.1.4. RSVP IPv6 Session 353 The value has the format below. The value fields are taken from 354 [RFC3209, sections 4.6.1.2 and 4.6.2.2]. 356 0 1 2 3 357 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 1 358 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 359 | IPv6 tunnel end point address | 360 | | 361 | | 362 | | 363 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 364 | Must Be Zero | Tunnel ID | 365 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 366 | Extended Tunnel ID | 367 | | 368 | | 369 | | 370 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 371 | IPv6 tunnel sender address | 372 | | 373 | | 374 | | 375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 376 | Must Be Zero | LSP ID | 377 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 379 3.1.5. VPN IPv4 Prefix 381 The value field consists of the Route Distinguisher advertised with 382 the VPN IPv4 prefix, the IPv4 prefix and a prefix length, as follows: 384 0 1 2 3 385 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 1 386 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 387 | Route Distinguisher | 388 | (8 octets) | 389 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 390 | IPv4 prefix | 391 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 392 | Prefix Length | Must Be Zero | 393 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 395 3.1.6. VPN IPv6 Prefix 397 The value field consists of the Route Distinguisher advertised with 398 the VPN IPv6 prefix, the IPv6 prefix and a prefix length, as follows: 400 0 1 2 3 401 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 1 402 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 403 | Route Distinguisher | 404 | (8 octets) | 405 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 406 | IPv6 prefix | 407 | | 408 | | 409 | | 410 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 411 | Prefix Length | Must Be Zero | 412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 414 3.1.7. L2 VPN Endpoint 416 The value field consists of a Route Distinguisher (8 octets), the 417 sender (of the ping)'s CE ID (2 octets), the receiver's CE ID (2 418 octets), and an encapsulation type (2 octets), formatted as follows: 420 0 1 2 3 421 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 1 422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 423 | Route Distinguisher | 424 | (8 octets) | 425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 426 | Sender's CE ID | Receiver's CE ID | 427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 428 | Encapsulation Type | Must Be Zero | 429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 431 3.1.8. L2 Circuit ID 433 The value field consists of a remote PE address (the address of the 434 targetted LDP session), a VC ID and an encapsulation type, as 435 follows: 437 0 1 2 3 438 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 1 439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 440 | Remote PE Address | 441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 442 | VC ID | 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 444 | Encapsulation Type | Must Be Zero | 445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 447 3.2. Downstream Mapping 449 The Downstream Mapping is an optional TLV in an echo request. The 450 Length is 16 + 4*M + 4*N octets, where M is the Multipath Length, and 451 N is the number of Downstream Labels. The Value field of a 452 Downstream Mapping has the following format: 454 0 1 2 3 455 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 1 456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 457 | Downstream IPv4 Address | 458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 459 | MTU | Address Type | DS Index | 460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 461 | Downstream Interface Address | 462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 463 | Hash Key Type | Depth Limit | No of Multipaths | 464 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 465 | IP Address or Next Label | 466 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 467 . . 468 . (more IP Addresses or Next Labels) . 469 . . 470 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 471 | Downstream Label | Protocol | 472 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 473 . . 474 . . 475 . . 476 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 477 | Downstream Label | Protocol | 478 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 480 If the interface to the downstream LSR is numbered, then the 481 Downstream IPv4 Address can either be the downstream LSR's Router ID 482 or the interface address of the downstream LSR. In this case, the 483 Address Type is set to IPv4 and the Downstream Interface Address is 484 set to the downstream LSR's interface address. If the interface to 485 the downstream LSR is unnumbered, the Downstream IPv4 Address MUST be 486 the downstream LSR's Router ID, and the Address Type MUST be 487 Unnumbered, and the Downstream Interface Address MUST be the index 488 assigned by the upstream LSR to the interface. 490 The MTU is the largest MPLS frame (including label stack) that fits 491 on the interface to the Downstream LSR. The Downstream Interface 492 Address Type is one of: 494 Type # Address Type 495 ------ ------------ 496 1 IPv4 497 2 Unnumbered 499 'Protocol' is taken from the following table: 501 Protocol # Signaling Protocol 502 ---------- ------------------ 503 0 Unknown 504 1 Static 505 2 BGP 506 3 LDP 507 4 RSVP-TE 508 5 Reserved; see Appendix 510 The notion of "downstream router" and "downstream interface" should 511 be explained. Consider an LSR X. If a packet that was originated 512 with TTL n>1 arrived with outermost label L at LSR X, X must be able 513 to compute which LSRs could receive the packet if it was originated 514 with TTL=n+1, over which interface the request would arrive and what 515 label stack those LSRs would see. (It is outside the scope of this 516 document to specify how this computation is done.) The set of these 517 LSRs/interfaces are the downstream routers/interfaces (and their 518 corresponding labels) for X with respect to L. Each pair of 519 downstream router and interface requires a separate Downstream 520 Mapping to be added to the reply, and is given a unique DS Index. 521 (Note that there are multiple Downstream Label fields in each TLV as 522 the incoming label L may be swapped with a label stack.) 524 The case where X is the LSR originating the echo request is a special 525 case. X needs to figure out what LSRs would receive the MPLS echo 526 request for a given FEC Stack that X originates with TTL=1. 528 The set of downstream routers at X may be alternative paths (see the 529 discussion below on ECMP) or simultaneous paths (e.g., for MPLS 530 multicast). In the former case, the Multipath sub-field is used as a 531 hint to the sender as to how it may influence the choice of these 532 alternatives. The "No of Multipaths" is the number of IP 533 Address/Next Label fields. The Hash Key Type is taken from the 534 following table: 536 Hash Key Type IP Address or Next Label 537 -------------------- ------------------------ 538 0 no multipath (nothing; M = 0) 539 1 label M labels 540 2 IP address M IP addresses 541 3 label range M/2 low/high label pairs 542 4 IP address range M/2 low/high address pairs 543 5 no more labels (nothing; M = 0) 544 6 All IP addresses (nothing; M = 0) 545 7 no match (nothing; M = 0) 547 The Depth Limit is applicable only to a label stack, and is the 548 maximum number of labels considered in the hash; this SHOULD be set 549 to zero if unspecified or unlimited. 551 IP Address or Next Label is an IP address from the range 127/8 or an 552 next label which will exercise this particular path. 554 The semantics of the Hash Key Type and IP Address/Next Label are as 555 follows: 557 type 1 - a list of single labels is provided, any one of which 558 will cause the hash to match this MP path. 559 type 2 - a list of single IP addresses is provided, any one of 560 which will cause the hash to match this MP path. 561 type 3 - a list of label ranges is provided, any one of which will 562 cause the hash to match this MP path. 563 type 4 - a list of IP address ranges is provided, any one of which 564 will cause the hash to match this MP path. 565 type 5 - if no more labels are provided on the stack, this MP path 566 will apply (can only appear once). 567 type 6 - Any IP addresses matches. Underlying labels may go 568 elsewhere, but all IP takes only one MP path (can only 569 appear once). 570 type 7 - no matches are possible given the set of "Multipath 571 Exercise TLV" provided by prior hops. 573 If prior hops provide a "Downstream Multipath Mapping TLV" the labels 574 and IP addresses should be picked from the set provided in prior 575 "Multipath Exercise TLV" or "Hash Key Type" of 7 used. 577 For example, suppose LSR X at hop 10 has two downstream LSRs Y and Z 578 for the FEC in question. X could return Hash Key Type 4, with 579 low/high IP addresses of 1.1.1.1->1.1.1.255 for downstream LSR Y and 580 2.1.1.1->2.1.1.255 for downstream LSR Z. The head end reflects this 581 information to LSR Y. Y, which has three downstream LSRs U, V and W, 582 computes that 1.1.1.1->1.1.1.127 would go to U and 1.1.1.128-> 583 1.1.1.255 would go to V. Y would then respond with 3 Downstream 584 Mappings: to U, with Hash Key Type 4 (1.1.1.1->1.1.1.127); to V, with 585 Hash Key Type 4 (1.1.1.127->1.1.1.255); and to W, with Hash Key Type 586 7. 588 3.3. Pad TLV 590 The value part of the Pad TLV contains a variable number (>= 1) of 591 octets. The first octet takes values from the following table; all 592 the other octets (if any) are ignored. The receiver SHOULD verify 593 that the TLV is received in its entirety, but otherwise ignores the 594 contents of this TLV, apart from the first octet. 596 Value Meaning 597 ----- ------- 598 1 Drop Pad TLV from reply 599 2 Copy Pad TLV to reply 600 3-255 Reserved for future use 602 3.4. Error Code 604 The Error Code TLV is currently not defined; its purpose is to 605 provide a mechanism for a more elaborate error reporting structure, 606 should the reason arise. 608 3.5. Vendor Enterprise Code 610 The Length is always 4; the value is the SMI Enterprise code, in 611 network octet order, of the vendor with a Vendor Private extension to 612 any of the fields in the fixed part of the message, in which case 613 this TLV MUST be present. If none of the fields in the fixed part of 614 the message have vendor private extensions, this TLV is OPTIONAL. 616 4. Theory of Operation 618 An MPLS echo request is used to test a particular LSP. The LSP to be 619 tested is identified by the "FEC Stack"; for example, if the LSP was 620 set up via LDP, and is to an egress IP address of 10.1.1.1, the FEC 621 stack contains a single element, namely, an LDP IPv4 prefix sub-TLV 622 with value 10.1.1.1/32. If the LSP being tested is an RSVP LSP, the 623 FEC stack consists of a single element that captures the RSVP Session 624 and Sender Template which uniquely identifies the LSP. 626 FEC stacks can be more complex. For example, one may wish to test a 627 VPN IPv4 prefix of 10.1/8 that is tunneled over an LDP LSP with 628 egress 10.10.1.1. The FEC stack would then contain two sub-TLVs, the 629 first being a VPN IPv4 prefix, and the second being an LDP IPv4 630 prefix. If the underlying (LDP) tunnel were not known, or was 631 considered irrelevant, the FEC stack could be a single element with 632 just the VPN IPv4 sub-TLV. 634 When an MPLS echo request is received, the receiver is expected to do 635 a number of tests that verify that the control plane and data plane 636 are both healthy (for the FEC stack being pinged), and that the two 637 planes are in sync. 639 4.1. Dealing with Equal-Cost Multi-Path (ECMP) 641 LSPs need not be simple point-to-point tunnels. Frequently, a single 642 LSP may originate at several ingresses, and terminate at several 643 egresses; this is very common with LDP LSPs. LSPs for a given FEC 644 may also have multiple "next hops" at transit LSRs. At an ingress, 645 there may also be several different LSPs to choose from to get to the 646 desired endpoint. Finally, LSPs may have backup paths, detour paths 647 and other alternative paths to take should the primary LSP go down. 649 To deal with the last two first: it is assumed that the LSR sourcing 650 MPLS echo requests can force the echo request into any desired LSP, 651 so choosing among multiple LSPs at the ingress is not an issue. The 652 problem of probing the various flavors of backup paths that will 653 typically not be used for forwarding data unless the primary LSP is 654 down will not be addressed here. 656 Since the actual LSP and path that a given packet may take may not be 657 known a priori, it is useful if MPLS echo requests can exercise all 658 possible paths. This, while desirable, may not be practical, because 659 the algorithms that a given LSR uses to distribute packets over 660 alternative paths may be proprietary. 662 To achieve some degree of coverage of alternate paths, there is a 663 certain lattitude in choosing the destination IP address and source 664 UDP port for an MPLS echo request. This is clearly not sufficient; 665 in the case of traceroute, more lattitude is offered by means of the 666 "Multipath Exercise" sub-TLV of the Downstream Mapping TLV. This is 667 used as follows. An ingress LSR periodically sends an MPLS 668 traceroute message to determine whether there are multipaths for a 669 given LSP. If so, each hop will provide some information how each of 670 its downstreams can be exercised. The ingress can then send MPLS 671 echo requests that exercise these paths. If several transit LSRs 672 have ECMP, the ingress may attempt to compose these to exercise all 673 possible paths. However, full coverage may not be possible. 675 4.2. Sending an MPLS Echo Request 677 An MPLS echo request is a (possibly) labelled UDP packet. The IP 678 header is set as follows: the source IP address is a routable address 679 of the sender; the destination IP address is a (randomly chosen) 680 address from 127/8; the IP TTL is set to 1. The source UDP port is 681 chosen by the sender; the destination UDP port is set to 3503 682 (assigned by IANA for MPLS echo requests). The Router Alert option 683 is set in the IP header. 685 If the echo request is labelled, one may (depending on what is being 686 pinged) set the TTL of the innermost label to 1, to prevent the ping 687 request going farther than it should. Examples of this include 688 pinging a VPN IPv4 or IPv6 prefix, an L2 VPN end point or an L2 689 circuit ID. This can also be accomplished by inserting a router 690 alert label above this label; however, this may lead to the undesired 691 side effect that MPLS echo requests take a different data path than 692 actual data. 694 In "ping" mode (end-to-end connectivity check), the TTL in the 695 outermost label is set to 255. In "traceroute" mode (fault isolation 696 mode), the TTL is set successively to 1, 2, .... 698 The sender chooses a Sender's Handle, and a Sequence Number. When 699 sending subsequent MPLS echo requests, the sender SHOULD increment 700 the sequence number by 1. However, a sender MAY choose to send a 701 group of echo requests with the same sequence number to improve the 702 chance of arrival of at least one packet with that sequence number. 704 The TimeStamp Sent is set to the time-of-day (in seconds and 705 microseconds) that the echo request is sent. The TimeStamp Received 706 is set to zero. 708 An MPLS echo request MUST have a FEC Stack TLV. Also, the Reply Mode 709 must be set to the desired reply mode; the Return Code and Subcode 710 are set to zero. 712 In the "traceroute" mode, the echo request SHOULD contain one or more 713 Downstream Mapping TLVs. For TTL=1, all the downstream routers (and 714 corresponding labels) for the sender with respect to the FEC Stack 715 being pinged SHOULD be sent in the echo request. For n>1, the 716 Downstream Mapping TLVs from the echo reply for TTL=(n-1) are copied 717 to the echo request with TTL=n; the sender MAY choose to reduce the 718 size of a "Downstream Multipath Mapping TLV" when copying into the 719 next echo request as long as the Hash Key Type matching the label or 720 IP address used to exercise the current MP is still present. 722 4.3. Receiving an MPLS Echo Request 724 An LSR X that receives an MPLS echo request first parses the packet 725 to ensure that it is a well-formed packet, and that the TLVs are 726 understood. If not, X SHOULD send an MPLS echo reply with the Return 727 Code set to "Malformed echo request received" or "TLV not understood" 728 (as appropriate), and the Subcode set to the appropriate value. 730 If the echo request is good, X then checks whether it is a valid 731 transit or egress LSR for the FEC in the echo request. If not, X MAY 732 log this fact. If it is, X notes that interface I over which the 733 echo was received, and the label L with which it came. X checks 734 whether it actually advertised L for the FEC in the echo request; X 735 MAY further check whether it expects L over interface I or not. 737 If the echo request contains a Downstream Mapping TLV, X MUST further 738 check whether its Router ID or one of its interface addresses matches 739 one of the Downstream IPv4 Address; if the Address Type is 740 Unnumbered, X further checks if the interface I has the given 741 (upstream) index. If these check out, X determines whether the given 742 Downstream Label is in fact the label that X sent as its mapping for 743 the FEC over the downstream interface. The result of the checks in 744 the previous and this paragraph are captured in the Return 745 Code/Subcode. 747 If the echo request has a Reply Mode that wants a reply, X uses the 748 procedure in the next subsection to send the echo reply. 750 4.4. Sending an MPLS Echo Reply 752 An MPLS echo reply is a UDP packet. It MUST ONLY be sent in response 753 to an MPLS echo request. The source IP address is a routable address 754 of the replier; the source port is the well-known UDP port for MPLS 755 ping. The destination IP address and UDP port are copied from the 756 source IP address and UDP port of the echo request. The IP TTL is 757 set to 255. If the Reply Mode in the echo request is "Reply via an 758 IPv4 UDP packet with Router Alert", then the IP header MUST contain 759 the Router Alert IP option. If the reply is sent over an LSP, the 760 topmost label MUST in this case be the Router Alert label (1) (see 761 [LABEL-STACK]). 763 The format of the echo reply is the same as the echo request. The 764 Sender's Handle, the Sequence Number and TimeStamp Sent are copied 765 from the echo request; the TimeStamp Received is set to the time-of- 766 day that the echo request is received (note that this information is 767 most useful if the time-of-day clocks on the requestor and the 768 replier are synchronized). The FEC Stack TLV from the echo request 769 MAY be copied to the reply. 771 The replier MUST fill in the Return Code and Subcode, as determined 772 in the previous subsection. 774 If the echo request contains a Pad TLV, the replier MUST interpret 775 the first octet for instructions regarding how to reply. 777 If the echo request contains a Downstream Mapping TLV, the replier 778 SHOULD compute its downstream routers and corresponding labels for 779 the incoming label, and add Downstream Mapping TLVs for each one to 780 the echo reply it sends back. 782 4.5. Receiving an MPLS Echo Reply 784 An LSR X should only receive an MPLS Echo Reply in response to an 785 MPLS Echo Request that it sent. Thus, on receipt of an MPLS Echo 786 Reply, X should parse the packet to assure that it is well-formed, 787 then attempt to match up the Echo Reply with an Echo Request that it 788 had previously sent, using the destination UDP port and the Sender's 789 Handle. If no match is found, then X jettisons the Echo Reply; 790 otherwise, it checks the Sequence Number to see if it matches. Gaps 791 in the Sequence Number MAY be logged and SHOULD be counted. Once an 792 Echo Reply is received for a given Sequence Number (for a given UDP 793 port and Handle), the Sequence Number for subsequent Echo Requests 794 for that UDP port and Handle SHOULD be incremented. 796 If the Echo Reply contains Downstream Mappings, and X wishes to 797 traceroute further, it SHOULD copy the Downstream Mappings into its 798 next Echo Request (with TTL incremented by one). 800 4.6. Non-compliant Routers 802 If the egress for the FEC Stack being pinged does not support MPLS 803 ping, then no reply will be sent, resulting in possible "false 804 negatives". If in "traceroute" mode, a transit LSR does not support 805 MPLS ping, then no reply will be forthcoming from that LSR for some 806 TTL, say n. The LSR originating the echo request SHOULD try sending 807 the echo request with TTL=n+1, n+2, ..., n+k in the hope that some 808 transit LSR further downstream may support MPLS echo requests and 809 reply. In such a case, the echo request for TTL>n MUST NOT have 810 Downstream Mapping TLVs, until a reply is received with a Downstream 811 Mapping. 813 Normative References 815 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 816 Requirement Levels", BCP 14, RFC 2119, March 1997. 818 [LABEL-STACK] Rosen, E., et al, "MPLS Label Stack Encoding", RFC 819 3032, January 2001. 821 [RSVP] Braden, R. (Editor), et al, "Resource ReSerVation protocol 822 (RSVP) -- Version 1 Functional Specification," RFC 2205, 823 September 1997. 825 [RSVP-REFRESH] Berger, L., et al, "RSVP Refresh Overhead Reduction 826 Extensions", RFC 2961, April 2001. 828 [RSVP-TE] Awduche, D., et al, "RSVP-TE: Extensions to RSVP for LSP 829 tunnels", RFC 3209, December 2001. 831 Informative References 833 [ICMP] Postel, J., "Internet Control Message Protocol", RFC 792. 835 [LDP] Andersson, L., et al, "LDP Specification", RFC 3036, January 836 2001. 838 Security Considerations 840 There are at least two approaches to attacking LSRs using the 841 mechanisms defined here. One is a Denial of Service attack, by 842 sending MPLS echo requests/replies to LSRs and thereby increasing 843 their workload. The other is obfuscating the state of the MPLS data 844 plane liveness by spoofing, hijacking, replaying or otherwise 845 tampering with MPLS echo requests and replies. 847 Authentication will help reduce the number of seemingly valid MPLS 848 echo requests, and thus cut down the Denial of Service attacks; 849 beyond that, each LSR must protect itself. 851 Authentication sufficiently addresses spoofing, replay and most 852 tampering attacks; one hopes to use some mechanism devised or 853 suggested by the RPSec WG. It is not clear how to prevent hijacking 854 (non-delivery) of echo requests or replies; however, if these 855 messages are indeed hijacked, MPLS ping will report that the data 856 plane isn't working as it should. 858 It doesn't seem vital (at this point) to secure the data carried in 859 MPLS echo requests and replies, although knowledge of the state of 860 the MPLS data plane may be considered confidential by some. 862 5. IANA Considerations 864 The TCP and UDP port number 3503 has been allocated by IANA for LSP 865 echo requests and replies. 867 The following sections detail the new name spaces to be managed by 868 IANA. For each of these name spaces, the space is divided into 869 assignment ranges; the following terms are used in describing the 870 procedures by which IANA allocates values: "Standards Action" (as 871 defined in [IANA]); "Expert Review" and "Vendor Private Use". 873 Values from "Expert Review" ranges MUST be registered with IANA, and 874 MUST be accompanied by an Experimental RFC that describes the format 875 and procedures for using the code point. 877 Values from "Vendor Private" ranges MUST NOT be registered with IANA; 878 however, the message MUST contain an enterprise code as registered 879 with the IANA SMI Network Management Private Enterprise Codes. For 880 each name space that has a Vendor Private range, it must be specified 881 where exactly the SMI Enterprise Code resides; see below for 882 examples. In this way, several enterprises (vendors) can use the 883 same code point without fear of collision. 885 5.1. Message Types, Reply Modes, Return Codes 887 It is requested that IANA maintain registries for Message Types, 888 Reply Modes, Return Codes and Return Subcodes. Each of these can 889 take values in the range 0-255. Assignments in the range 0-191 are 890 via Standards Action; assignments in the range 192-251 are made via 891 Expert Review; values in the range 252-255 are for Vendor Private 892 Use, and MUST NOT be allocated. 894 If any of these fields fall in the Vendor Private range, a top-level 895 Vendor Enterprise Code TLV MUST be present in the message. 897 5.2. TLVs 899 It is requested that IANA maintain registries for the Type field of 900 top-level TLVs as well as for sub-TLVs. The valid range for each of 901 these is 0-65535. Assignments in the range 0-32767 are made via 902 Standards Action; assignments in the range 32768-64511 are made via 903 Expert Review; values in the range 64512-65535 are for Vendor Private 904 Use, and MUST NOT be allocated. 906 If a TLV or sub-TLV has a Type that falls in the range for Vendor 907 Private Use, the Length MUST be at least 4, and the first four octets 908 MUST be that vendor's SMI Enterprise Code, in network octet order. 909 The rest of the Value field is private to the vendor. 911 Acknowledgments 913 This document is the outcome of many discussions among many people, 914 that include Manoj Leelanivas, Paul Traina, Yakov Rekhter, Der-Hwa 915 Gan, Brook Bailey, Eric Rosen and Ina Minei. 917 The Multipath Exercise sub-field of the Downstream Mapping TLV was 918 adapted from text suggested by Curtis Villamizar. 920 Appendix 922 This appendix specifies non-normative aspects of detecting MPLS data 923 plane liveness. 925 5.1. CR-LDP FEC 927 This section describes how a CR-LDP FEC can be included in an Echo 928 Request using the following FEC subtype: 930 Sub-Type # Length Value Field 931 ---------- ------ ----------- 932 5 6 CR-LDP LSP ID 934 The value consists of the LSPID of the LSP being pinged. An LSPID is 935 a four octet IPv4 address (a local address on the ingress LSR, for 936 example, the Router ID) plus a two octet identifier that is unique 937 per LSP on a given ingress LSR. 939 0 1 2 3 940 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 1 941 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 942 | Ingress LSR Router ID | 943 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 944 | Must Be Zero | LSP ID | 945 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 947 5.2. Downstream Mapping for CR-LDP 949 If a label in a Downstream Mapping was learned via CR-LDP, the 950 Protocol field in the Mapping TLV can use the following entry: 952 Protocol # Signaling Protocol 953 ---------- ------------------ 954 5 CR-LDP 956 Authors' Addresses 958 Kireeti Kompella 959 Nischal Sheth 960 Juniper Networks 961 1194 N.Mathilda Ave 962 Sunnyvale, CA 94089 963 e-mail: kireeti@juniper.net 964 e-mail: nsheth@juniper.net 966 Ping Pan 967 Ciena 968 10480 Ridgeview Court 969 Cupertino, CA 95014 970 e-mail: ppan@ciena.com 971 phone: +1 408.366.4700 973 Dave Cooper 974 Global Crossing 975 960 Hamlin Court 976 Sunnyvale, CA 94089 977 email: dcooper@gblx.net 978 phone: +1 916.415.0437 980 George Swallow 981 Cisco Systems, Inc. 982 250 Apollo Drive 983 Chelmsford, MA 01824 984 e-mail: swallow@cisco.com 985 phone: +1 978.497.8143 987 Sanjay Wadhwa 988 Juniper Networks 989 10 Technology Park Drive 990 Westford, MA 01886-3146 991 email: swadhwa@unispherenetworks.com 992 phone: +1 978.589.0697 994 Ronald P. Bonica 995 WorldCom 996 22001 Loudoun County Pkwy 997 Ashburn, Virginia, 20147 998 email: ronald.p.bonica@wcom.com 999 phone: +1 703.886.1681 1001 Intellectual Property Rights Notices 1003 The IETF takes no position regarding the validity or scope of any 1004 intellectual property or other rights that might be claimed to 1005 pertain to the implementation or use of the technology described in 1006 this document or the extent to which any license under such rights 1007 might or might not be available; neither does it represent that it 1008 has made any effort to identify any such rights. Information on the 1009 IETF's procedures with respect to rights in standards-track and 1010 standards-related documentation can be found in BCP-11. 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