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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-04) exists of draft-ietf-bfd-rfc5884-clarifications-02 == Outdated reference: A later version (-06) exists of draft-kumarkini-mpls-spring-lsp-ping-04 == Outdated reference: A later version (-08) exists of draft-previdi-6man-segment-routing-header-07 ** Obsolete normative reference: RFC 4379 (Obsoleted by RFC 8029) Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MPLS Working Group G. Mirsky 3 Internet-Draft J. Tantsura 4 Intended status: Standards Track Ericsson 5 Expires: March 3, 2016 I. Varlashkin 6 Google 7 M. Chen 8 Huawei 9 August 31, 2015 11 Bidirectional Forwarding Detection (BFD) Directed Return Path 12 draft-ietf-mpls-bfd-directed-00 14 Abstract 16 Bidirectional Forwarding Detection (BFD) is expected to monitor bi- 17 directional paths. When a BFD session monitors in its forward 18 direction an explicitly routed path there is a need to be able to 19 direct egress BFD peer to use specific path as reverse direction of 20 the BFD session. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on March 3, 2016. 39 Copyright Notice 41 Copyright (c) 2015 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 1.1. Conventions used in this document . . . . . . . . . . . . 3 58 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 59 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3 60 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 61 3. Direct Reverse BFD Path . . . . . . . . . . . . . . . . . . . 4 62 3.1. Case of MPLS Data Plane . . . . . . . . . . . . . . . . . 4 63 3.1.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . 4 64 3.1.2. Static and RSVP-TE sub-TLVs . . . . . . . . . . . . . 5 65 3.1.3. Segment Routing Tunnel sub-TLV . . . . . . . . . . . 5 66 3.2. Case of IPv6 Data Plane . . . . . . . . . . . . . . . . . 6 67 3.3. Bootstrapping BFD session with BFD Reverse Path over 68 Segment Routed tunnel . . . . . . . . . . . . . . . . . . 6 69 3.4. Return Codes . . . . . . . . . . . . . . . . . . . . . . 7 70 4. Use Case Scenario . . . . . . . . . . . . . . . . . . . . . . 7 71 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 72 5.1. TLV . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 73 5.2. Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 8 74 5.3. Return Codes . . . . . . . . . . . . . . . . . . . . . . 8 75 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 76 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 77 8. Normative References . . . . . . . . . . . . . . . . . . . . 9 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 80 1. Introduction 82 RFC 5880 [RFC5880], RFC 5881 [RFC5881], and RFC 5883 [RFC5883] 83 established the BFD protocol for IP networks and RFC 5884 [RFC5884] 84 set rules of using BFD asynchronous mode over IP/MPLS LSPs. All 85 standards implicitly assume that the egress BFD peer will use the 86 shortest path route regardless of route being used to send BFD 87 control packets towards it. As result, if the ingress BFD peer sends 88 its BFD control packets over explicit path that is diverging from the 89 best route, then reverse direction of the BFD session is likely not 90 to be on co-routed bi-directional path with the forward direction of 91 the BFD session. And because BFD control packets are not guaranteed 92 to cross the same links and nodes in both directions detection of 93 Loss of Continuity (LoC) defect in forward direction may demonstrate 94 positive negatives. 96 This document defines the extension to LSP Ping [RFC4379], BFD 97 Reverse Path TLV, and proposes that it to be used to instruct the 98 egress BFD peer to use explicit path for its BFD control packets 99 associated with the particular BFD session. The TLV will be 100 allocated from the TLV and sub-TLV registry defined by RFC 4379 101 [RFC4379]. As a special case, forward and reverse directions of the 102 BFD session can form bi-directional co-routed associated channel. 104 1.1. Conventions used in this document 106 1.1.1. Terminology 108 BFD: Bidirectional Forwarding Detection 110 MPLS: Multiprotocol Label Switching 112 LSP: Label Switching Path 114 LoC: Loss of Continuity 116 1.1.2. Requirements Language 118 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 119 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 120 "OPTIONAL" in this document are to be interpreted as described in 121 [RFC2119]. 123 2. Problem Statement 125 BFD is best suited to monitor bi-directional co-routed paths. In 126 most cases, given stable environments, the forward and reverse 127 direction between two nodes is likely to be co-routed, this 128 fulfilling the implicit BFD requirements. If BFD is used to monitor 129 unidirectional explicitly routed paths, e.g. MPLS-TE LSPs, its 130 control packets in forward direction would be in-band using the 131 mechanism defined in [RFC5884] and [RFC5586]. But the reverse 132 direction of the BFD session would still follow the shortest path 133 route and that might lead to the following problems detecting 134 failures on the unidirectional explicit path: 136 o detection of a failure on the reverse path cannot reliably be 137 interpreted as bi-directional defect and thus trigger, for 138 example, protection switchover of the forward direction; 140 o if a failure of the reverse path had been ignored, the ingress 141 node would not receive indication of forward direction failure 142 from its egress peer. 144 To address these challenges the egress BFD peer should be instructed 145 to use specific path for its control packets. 147 3. Direct Reverse BFD Path 149 3.1. Case of MPLS Data Plane 151 LSP ping, defined in [RFC4379], uses BFD Discriminator TLV [RFC5884] 152 to bootstrap a BFD session over an MPLS LSP. This document defines a 153 new TLV, BFD Reverse Path TLV, that MUST contain a single sub-TLV 154 that can be used to carry information about reverse path for the 155 specified in BFD Discriminator TLV session. 157 3.1.1. BFD Reverse Path TLV 159 The BFD Reverse Path TLV is an optional TLV within the LSP ping 160 protocol. However, if used, the BFD Discriminator TLV MUST be 161 included in an Echo Request message as well. If the BFD 162 Discriminator TLV is not present when the BFD Reverse Path TLV is 163 included, then it MUST be treated as malformed Echo Request, as 164 described in [RFC4379]. 166 The BFD Reverse Path TLV carries the specified path that BFD control 167 packets of the BFD session referenced in the BFD Discriminator TLV 168 are required to follow. The format of the BFD Reverse Path TLV is as 169 presented in Figure 1. 171 0 1 2 3 172 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 1 173 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 174 | BFD Reverse Path TLV Type | Length | 175 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 176 | Reverse Path | 177 ~ ~ 178 | | 179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 181 Figure 1: BFD Reverse Path TLV 183 BFD Reverse Path TLV Type is 2 octets in length and value to be 184 assigned by IANA. 186 Length is 2 octets in length and defines the length in octets of the 187 Reverse Path field. 189 Reverse Path field contains a sub-TLV. Any Target FEC sub-TLV, 190 already or in the future defined, from IANA sub-registry Sub-TLVs for 191 TLV Types 1, 16, and 21 of MPLS LSP Ping Parameters registry MAY be 192 used in this field. Only one sub-TLV MUST be included in the Reverse 193 Path TLV. If more than one sub-TLVs are present in the Reverse Path 194 TLV, then only the first sub-TLV MUST be used and the rest MUST be 195 silently discarded. 197 If the egress LSR cannot find path specified in the Reverse Path TLV 198 it MUST send Echo Reply with the received Reverse Path TLV and set 199 the return code to "Failed to establish the BFD session. The 200 specified reverse path was not found" Section 3.4. The egress LSR 201 MAY establish the BFD session over IP network according to [RFC5884]. 203 3.1.2. Static and RSVP-TE sub-TLVs 205 When explicit path on MPLS data plane set either as Static or RSVP-TE 206 LSP respective sub-TLVs defined in [RFC7110] identify explicit return 207 path. 209 3.1.3. Segment Routing Tunnel sub-TLV 211 In addition to Static and RSVP-TE, Segment Routing with MPLS data 212 plane can be used to set explicit path. In this case a new sub-TLV 213 is defined in this document as presented in Figure 2. 215 0 1 2 3 216 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 1 217 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 218 | SegRouting MPLS sub-TLV Type | Length | 219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 220 | Label Entry 1 | 221 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 222 | Label Entry 2 | 223 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 224 ~ ~ 225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 226 | Label Entry N | 227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 229 Figure 2: Segment Routing MPLS Tunnel sub-TLV 231 The Segment Routing Tunnel sub-TLV Type is two octets in length, and 232 will be allocated by IANA. 234 The egress LSR MUST use the Value field as label stack for BFD 235 control packets for the BFD session identified by source IP address 236 and value in BFD Discriminator TLV. 238 The Segment Routing Tunnel sub-TLV MAY be used in Reply Path TLV 239 defined in [RFC7110] 241 3.2. Case of IPv6 Data Plane 243 IPv6 can be data plane of choice for Segment Routed tunnels 244 [I-D.previdi-6man-segment-routing-header]. In such networks the BFD 245 Reverse Path TLV described in Section 3.1.1 can be used as well. To 246 specify reverse path of a BFD session in IPv6 environment the BFD 247 Discriminator TLV MUST be used along with the BFD Reverse Path TLV. 248 The BFD Reverse Path TLV in IPv6 network MUST include sub-TLV. 250 0 1 2 3 251 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 1 252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 253 | SegRouting IPv6 sub-TLV Type | Length | 254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 | | 256 | IPv6 Prefix | 257 | | 258 | | 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 260 | | 261 | IPv6 Prefix | 262 | | 263 | | 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 265 ~ ~ 266 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 268 Figure 3: Segment Routing IPv6 Tunnel sub-TLV 270 3.3. Bootstrapping BFD session with BFD Reverse Path over Segment 271 Routed tunnel 273 As discussed in [I-D.kumarkini-mpls-spring-lsp-ping] introduction of 274 Segment Routing network domains with MPLS data plane adds three new 275 sub-TLVs that may be used with Target FEC TLV. Section 6.1 addresses 276 use of new sub-TLVs in Target FEC TLV in LSP ping and LSP traceroute. 277 For the case of LSP ping the [I-D.kumarkini-mpls-spring-lsp-ping] 278 states that: 280 "Initiator MUST include FEC(s) corresponding to the destination 281 segment. 283 Initiator, i.e. ingress LSR, MAY include FECs corresponding to some 284 or all of segments imposed in the label stack by the ingress LSR to 285 communicate the segments traversed. " 286 When LSP ping is used to bootstrap BFD session this document updates 287 this and defines that LSP Ping MUST include the FEC corresponding to 288 the destination segment and SHOULD NOT include FECs corresponding to 289 some or all of segment imposed by the ingress LSR. Operationally 290 such restriction would not cause any problem or uncertainty as LSP 291 ping with FECs corresponding to some or all segments or traceroute 292 MAY precede the LSP ping that bootstraps the BFD session. 294 3.4. Return Codes 296 This document defines the following Return Codes: 298 o "Failed to establish the BFD session. The specified reverse path 299 was not found", (TBD4). When a specified reverse path is not 300 available at the egress LSR, an Echo Reply with the return code 301 set to "Failed to establish the BFD session. The specified 302 reverse path was not found" MUST be sent back to the ingress LSR . 303 (Section 3.1.1) 305 4. Use Case Scenario 307 In network presented in Figure 4 node A monitors two tunnels to node 308 H: A-B-C-D-G-H and A-B-E-F-G-H. To bootstrap BFD session to monitor 309 the first tunnel, node A MUST include BFD Discriminator TLV with 310 Discriminator value foobar-1 and MAY include BFD Reverse Path TLV 311 that references H-G-D-C-B-A tunnel. To bootstrap BFD session to 312 monitor the second tunnel, node A MUST include BFD Discriminator TLV 313 with Discriminator value foobar-2 314 [I-D.ietf-bfd-rfc5884-clarifications] and MAY include BFD Reverse 315 Path TLV that references H-G-F-E-B-A tunnel. 317 C---------D 318 | | 319 A-------B G-----H 320 | | 321 E---------F 323 Figure 4: Use Case for BFD Reverse Path TLV 325 If an operator needs node H to monitor path to node A, e.g. 326 H-G-D-C-B-A tunnel, then by looking up list of known Reverse Paths it 327 MAY find and use existing BFD sessions. 329 5. IANA Considerations 330 5.1. TLV 332 The IANA is requested to assign a new value for BFD Reverse Path TLV 333 from the "Multiprotocol Label Switching Architecture (MPLS) Label 334 Switched Paths (LSPs) Ping Parameters - TLVs" registry, "TLVs and 335 sub-TLVs" sub-registry. 337 +----------+----------------------+---------------+ 338 | Value | Description | Reference | 339 +----------+----------------------+---------------+ 340 | X (TBD1) | BFD Reverse Path TLV | This document | 341 +----------+----------------------+---------------+ 343 Table 1: New BFD Reverse Type TLV 345 5.2. Sub-TLV 347 The IANA is requested to assign two new sub-TLV types from 348 "Multiprotocol Label Switching Architecture (MPLS) Label Switched 349 Paths (LSPs) Ping Parameters - TLVs" registry, "Sub-TLVs for TLV 350 Types 1, 16, and 21" sub-registry. 352 +----------+-------------------------------------+---------------+ 353 | Value | Description | Reference | 354 +----------+-------------------------------------+---------------+ 355 | X (TBD2) | Segment Routing MPLS Tunnel sub-TLV | This document | 356 | X (TBD3) | Segment Routing IPv6 Tunnel sub-TLV | This document | 357 +----------+-------------------------------------+---------------+ 359 Table 2: New Segment Routing Tunnel sub-TLV 361 5.3. Return Codes 363 The IANA is requested to assign a new Return Code value from the 364 "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) 365 Ping Parameters" registry, "Return Codes" sub-registry, as follows 366 using a Standards Action value. 368 +----------+----------------------------------------+---------------+ 369 | Value | Description | Reference | 370 +----------+----------------------------------------+---------------+ 371 | X (TBD4) | Failed to establish the BFD session. | This document | 372 | | The specified reverse path was not | | 373 | | found. | | 374 +----------+----------------------------------------+---------------+ 376 Table 3: New Return Code 378 6. Security Considerations 380 Security considerations discussed in [RFC5880], [RFC5884], and 381 [RFC4379], apply to this document. 383 7. Acknowledgements 385 8. Normative References 387 [I-D.ietf-bfd-rfc5884-clarifications] 388 Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S. 389 Aldrin, "Clarifications to RFC 5884", draft-ietf-bfd- 390 rfc5884-clarifications-02 (work in progress), June 2015. 392 [I-D.kumarkini-mpls-spring-lsp-ping] 393 Kumar, N., Swallow, G., Pignataro, C., Akiya, N., Kini, 394 S., Gredler, H., and M. Chen, "Label Switched Path (LSP) 395 Ping/Trace for Segment Routing Networks Using MPLS 396 Dataplane", draft-kumarkini-mpls-spring-lsp-ping-04 (work 397 in progress), July 2015. 399 [I-D.previdi-6man-segment-routing-header] 400 Previdi, S., Filsfils, C., Field, B., Leung, I., Vyncke, 401 E., and D. Lebrun, "IPv6 Segment Routing Header (SRH)", 402 draft-previdi-6man-segment-routing-header-07 (work in 403 progress), July 2015. 405 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 406 Requirement Levels", BCP 14, RFC 2119, 407 DOI 10.17487/RFC2119, March 1997, 408 . 410 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 411 Label Switched (MPLS) Data Plane Failures", RFC 4379, 412 DOI 10.17487/RFC4379, February 2006, 413 . 415 [RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., 416 "MPLS Generic Associated Channel", RFC 5586, 417 DOI 10.17487/RFC5586, June 2009, 418 . 420 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 421 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 422 . 424 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 425 (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, 426 DOI 10.17487/RFC5881, June 2010, 427 . 429 [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 430 (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883, 431 June 2010, . 433 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 434 "Bidirectional Forwarding Detection (BFD) for MPLS Label 435 Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884, 436 June 2010, . 438 [RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord, 439 "Return Path Specified Label Switched Path (LSP) Ping", 440 RFC 7110, DOI 10.17487/RFC7110, January 2014, 441 . 443 Authors' Addresses 445 Greg Mirsky 446 Ericsson 448 Email: gregory.mirsky@ericsson.com 450 Jeff Tantsura 451 Ericsson 453 Email: jeff.tantsura@ericsson.com 455 Ilya Varlashkin 456 Google 458 Email: Ilya@nobulus.com 460 Mach(Guoyi) Chen 461 Huawei 463 Email: mach.chen@huawei.com