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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MPLS Working Group G. Mirsky 3 Internet-Draft Ericsson 4 Intended status: Standards Track J. Tantsura 5 Expires: 18 August 2022 Juniper Networks 6 I. Varlashkin 7 Google 8 M. Chen 9 Huawei 10 14 February 2022 12 Bidirectional Forwarding Detection (BFD) Directed Return Path for MPLS 13 Label Switched Paths (LSPs) 14 draft-ietf-mpls-bfd-directed-19 16 Abstract 18 Bidirectional Forwarding Detection (BFD) is expected to be able to 19 monitor a wide variety of encapsulations of paths between systems. 20 When a BFD session monitors an explicitly routed unidirectional path 21 there may be a need to direct egress BFD peer to use a specific path 22 for the reverse direction of the BFD session. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on 18 August 2022. 41 Copyright Notice 43 Copyright (c) 2022 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 48 license-info) in effect on the date of publication of this document. 49 Please review these documents carefully, as they describe your rights 50 and restrictions with respect to this document. Code Components 51 extracted from this document must include Revised BSD License text as 52 described in Section 4.e of the Trust Legal Provisions and are 53 provided without warranty as described in the Revised BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 1.1. Conventions used in this document . . . . . . . . . . . . 3 59 1.1.1. Requirements Language . . . . . . . . . . . . . . . . 3 60 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 61 3. Control of the Reverse BFD Path . . . . . . . . . . . . . . . 3 62 3.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 3 63 3.2. Return Codes . . . . . . . . . . . . . . . . . . . . . . 5 64 4. Use Case Scenario . . . . . . . . . . . . . . . . . . . . . . 5 65 5. Operational Considerations . . . . . . . . . . . . . . . . . 6 66 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 67 6.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 6 68 6.2. Return Code . . . . . . . . . . . . . . . . . . . . . . . 7 69 7. Implementation Status . . . . . . . . . . . . . . . . . . . . 7 70 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 71 9. Normative References . . . . . . . . . . . . . . . . . . . . 8 72 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 9 73 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 75 1. Introduction 77 [RFC5880], [RFC5881], and [RFC5883] established the BFD protocol for 78 IP networks. [RFC5884] and [RFC7726] set rules for using BFD 79 asynchronous mode over IP/MPLS LSPs, while not defining means to 80 control the path an egress BFD system uses to send BFD control 81 packets towards the ingress BFD system. 83 For the case when BFD is used to detect defects of the traffic 84 engineered LSP the path the BFD control packets transmitted by the 85 egress BFD system toward the ingress may be disjoint from the LSP in 86 the forward direction. The fact that BFD control packets are not 87 guaranteed to follow the same links and nodes in both forward and 88 reverse directions may be one of the factors contributing to 89 producing false positive defect notifications, i.e., false alarms, at 90 the ingress BFD peer. Ensuring that both directions of the BFD 91 session use co-routed paths may, in some environments, improve the 92 determinism of the failure detection and localization. 94 This document defines the BFD Reverse Path TLV as an extension to LSP 95 Ping [RFC8029] and proposes that it is to be used to instruct the 96 egress BFD system to use an explicit path for its BFD control packets 97 associated with a particular BFD session. The TLV will be allocated 98 from the TLV and sub-TLV registry defined in [RFC8029]. As a special 99 case, forward and reverse directions of the BFD session can form a 100 bi-directional co-routed associated channel. 102 1.1. Conventions used in this document 104 1.1.1. Requirements Language 106 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 107 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 108 "OPTIONAL" in this document are to be interpreted as described in BCP 109 14 [RFC2119] [RFC8174] when, and only when, they appear in all 110 capitals, as shown here. 112 2. Problem Statement 114 When BFD is used to monitor explicitly routed unidirectional path, 115 e.g., MPLS-TE LSP, BFD control packets in forward direction would be 116 in-band using the mechanism defined in [RFC5884]. But the reverse 117 direction of the BFD session would follow the shortest path route and 118 that might lead to the problem in detecting failures on an explicit 119 unidirectional path, as described below: 121 * detection by an ingress node of a failure on the reverse path may 122 not be unambiguously interpreted as the failure of the path in the 123 forward direction. 125 To address this scenario, the egress BFD peer would be instructed to 126 use a specific path for BFD control packets. 128 3. Control of the Reverse BFD Path 130 To bootstrap a BFD session over an MPLS LSP, LSP ping, defined in 131 [RFC8029], MUST be used with BFD Discriminator TLV [RFC5884]. This 132 document defines a new TLV, BFD Reverse Path TLV, that MAY contain 133 none, one or more sub-TLVs that can be used to carry information 134 about the reverse path for the BFD session that is specified by the 135 value in BFD Discriminator TLV. 137 3.1. BFD Reverse Path TLV 139 The BFD Reverse Path TLV is an optional TLV within the LSP ping 140 [RFC8029]. However, if used, the BFD Discriminator TLV MUST be 141 included in an Echo Request message as well. If the BFD 142 Discriminator TLV is not present when the BFD Reverse Path TLV is 143 included; then it MUST be treated as malformed Echo Request, as 144 described in [RFC8029]. 146 The BFD Reverse Path TLV carries information about the path onto 147 which the egress BFD peer of the BFD session referenced by the BFD 148 Discriminator TLV MUST transmit BFD control packets. The format of 149 the BFD Reverse Path TLV is as presented in Figure 1. 151 0 1 2 3 152 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 1 153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 154 | BFD Reverse Path TLV Type | Length | 155 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 156 | Reverse Path | 157 ~ ~ 158 | | 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 161 Figure 1: BFD Reverse Path TLV 163 BFD Reverse Path TLV Type is two octets in length and has a value of 164 TBD1 (to be assigned by IANA as requested in Section 6). 166 Length field is two octets long and defines the length in octets of 167 the Reverse Path field. 169 Reverse Path field contains none, one or more sub-TLVs. Any non- 170 multicast Target FEC Stack sub-TLV (already defined, or to be defined 171 in the future) for TLV Types 1, 16, and 21 of MPLS LSP Ping 172 Parameters registry MAY be used in this field. Multicast Target FEC 173 Stack sub-TLVs, i.e., p2mp and mp2mp, SHOULD NOT be included in 174 Reverse Path field. If the egress LSR finds multicast Target Stack 175 sub-TLV, it MUST send echo reply with the received Reverse Path TLV, 176 BFD Discriminator TLV and set the Return Code to "Inappropriate 177 Target FEC Stack sub-TLV present" Section 3.2. None, one or more 178 sub-TLVs MAY be included in the BFD Reverse Path TLV. If no sub-TLVs 179 are found in the BFD Reverse Path TLV, the egress BFD peer MUST 180 revert to using the local policy-based decision as described in 181 Section 7 [RFC5884], i.e., routed over IP network. 183 If the egress LSR cannot find the path specified in the Reverse Path 184 TLV it MUST send Echo Reply with the received BFD Discriminator TLV, 185 Reverse Path TLV and set the Return Code to "Failed to establish the 186 BFD session. The specified reverse path was not found" Section 3.2. 187 An implementation MAY provide configuration options to define action 188 at the egress BFD peer. For example, if the egress LSR cannot find 189 the path specified in the Reverse Path TLV, it MAY establish the BFD 190 session over an IP network, as defined in [RFC5884]. 192 The BFD Reverse Path TLV MAY be used in the bootstrapping of a BFD 193 session process described in Section 6 [RFC5884]. A system that 194 supports this specification MUST support using the BFD Reverse Path 195 TLV after the BFD session has been established. If a system that 196 supports this specification receives an LSP Ping with the BFD 197 Discriminator TLV and no BFD Reverse Path TLV even though the reverse 198 path for the specified BFD session has been established according to 199 the previously received BFD Reverse Path TLV, the egress LSR MUST 200 transition to transmitting periodic BFD Control messages as defined 201 in Section 7 [RFC5884]. 203 3.2. Return Codes 205 This document defines the following Return Codes for MPLS LSP Echo 206 Reply: 208 * "Inappropriate Target FEC Stack sub-TLV present", (TBD3). When 209 multicast Target FEC Stack sub-TLV found in the received Echo 210 Request by the egress BFD peer, an Echo Reply with the return code 211 set to "Inappropriate Target FEC Stack sub-TLV present" MUST be 212 sent to the ingress BFD peer Section 3.1. 214 * "Failed to establish the BFD session. The specified reverse path 215 was not found", (TBD4). When a specified reverse path is not 216 available at the egress BFD peer, an Echo Reply with the return 217 code set to "Failed to establish the BFD session. The specified 218 reverse path was not found" MUST be sent back to the ingress BFD 219 peer Section 3.1. 221 4. Use Case Scenario 223 In the network presented in Figure 2 node A monitors two tunnels to 224 node H: A-B-C-D-G-H and A-B-E-F-G-H. To bootstrap a BFD session to 225 monitor the first tunnel, node A MUST include a BFD Discriminator TLV 226 with Discriminator value (e.g., foobar-1) and MAY include a BFD 227 Reverse Path TLV that references H-G-D-C-B-A tunnel. To bootstrap a 228 BFD session to monitor the second tunnel, node A MUST include a BFD 229 Discriminator TLV with a different Discriminator value (e.g., foobar- 230 2) [RFC7726] and MAY include a BFD Reverse Path TLV that references 231 H-G-F-E-B-A tunnel. 233 C---------D 234 | | 235 A-------B G-----H 236 | | 237 E---------F 238 Figure 2: Use Case for BFD Reverse Path TLV 240 If an operator needs node H to monitor a path to node A, e.g. 241 H-G-D-C-B-A tunnel, then by looking up the list of known Reverse 242 Paths it MAY find and use the existing BFD session. 244 5. Operational Considerations 246 When an explicit path is set either as Static or RSVP-TE LSP, 247 corresponding sub-TLVs, defined in [RFC7110], MAY be used to identify 248 the explicit reverse path for the BFD session. If any of defined in 249 [RFC7110] sub-TLVs used in BFD Reverse Path TLV, then the periodic 250 verification of the control plane against the data plane, as 251 recommended in Section 4 [RFC5884], MUST use the Return Path TLV, as 252 per [RFC7110], with that sub-TLV. By using the LSP Ping with Return 253 Path TLV, an operator monitors whether at the egress BFD node the 254 reverse LSP is mapped to the same FEC as the BFD session. Selection 255 and control of the rate of LSP Ping with Return Path TLV follows the 256 recommendation of [RFC5884]: "The rate of generation of these LSP 257 Ping Echo request messages SHOULD be significantly less than the rate 258 of generation of the BFD Control packets. An implementation MAY 259 provide configuration options to control the rate of generation of 260 the periodic LSP Ping Echo request messages." 262 Suppose an operator planned network maintenance activity that 263 possibly affects FEC used in the BFD Reverse Path TLV. In that case, 264 the operator MUST avoid the unnecessary disruption using the LSP Ping 265 with a new FEC in the BFD Reverse Path TLV. But in some scenarios, 266 proactive measures cannot be taken. Because the frequency of LSP 267 Ping messages will be lower than the defect detection time provided 268 by the BFD session. As a result, a change in the reverse-path FEC 269 will first be detected as the BFD session's failure. In such a case, 270 the ingress BFD node SHOULD immediately transmit the LSP Ping Echo 271 request with Return Path TLV to verify whether the FEC is still 272 valid. If the failure was caused by the change in the FEC used for 273 the reverse direction of the BFD session, the ingress BFD node SHOULD 274 bootstrap a new BFD session using another FEC in BFD Reverse Path 275 TLV. 277 6. IANA Considerations 279 6.1. BFD Reverse Path TLV 281 The IANA is requested to assign a new value for BFD Reverse Path TLV 282 from the "Multiprotocol Label Switching Architecture (MPLS) Label 283 Switched Paths (LSPs) Ping Parameters - TLVs" registry, "TLVs and 284 sub-TLVs" sub-registry. 286 +=========+======================+===============+ 287 | Value | Description | Reference | 288 +=========+======================+===============+ 289 | (TBD1) | BFD Reverse Path TLV | This document | 290 +---------+----------------------+---------------+ 292 Table 1: New BFD Reverse Type TLV 294 6.2. Return Code 296 The IANA is requested to assign a new Return Code value from the 297 "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) 298 Ping Parameters" registry, "Return Codes" sub-registry, as follows 299 using a Standards Action value. 301 +=========+=============================+===============+ 302 | Value | Description | Reference | 303 +=========+=============================+===============+ 304 | (TBD3) | Inappropriate Target FEC | This document | 305 | | Stack sub-TLV present. | | 306 +---------+-----------------------------+---------------+ 307 | (TBD4) | Failed to establish the BFD | This document | 308 | | session. The specified | | 309 | | reverse path was not found. | | 310 +---------+-----------------------------+---------------+ 312 Table 2: New Return Code 314 7. Implementation Status 316 - The organization responsible for the implementation: ZTE 317 Corporation. 319 - The implementation's name ROSng empowers traditional routers, e.g., 320 ZXCTN 6000. 322 - A brief general description: A Return Path can be specified for a 323 BFD session over RSVP tunnel or LSP. The same can be specified for a 324 backup RSVP tunnel/LSP. 326 The implementation's level of maturity: production. 328 - Coverage: RSVP LSP (no support for Static LSP) 330 - Version compatibility: draft-ietf-mpls-bfd-directed-10. 332 - Licensing: proprietary. 334 - Implementation experience: simple once you support RFC 7110. 336 - Contact information: Qian Xin qian.xin2@zte.com.cn 338 - The date when information about this particular implementation was 339 last updated: 12/16/2019 341 Note to RFC Editor: This section MUST be removed before publication 342 of the document. 344 8. Security Considerations 346 Security considerations discussed in [RFC5880], [RFC5884], [RFC7726], 347 [RFC8029], and [RFC7110] apply to this document. 349 9. Normative References 351 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 352 Requirement Levels", BCP 14, RFC 2119, 353 DOI 10.17487/RFC2119, March 1997, 354 . 356 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 357 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 358 . 360 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 361 (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, 362 DOI 10.17487/RFC5881, June 2010, 363 . 365 [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 366 (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883, 367 June 2010, . 369 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 370 "Bidirectional Forwarding Detection (BFD) for MPLS Label 371 Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884, 372 June 2010, . 374 [RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord, 375 "Return Path Specified Label Switched Path (LSP) Ping", 376 RFC 7110, DOI 10.17487/RFC7110, January 2014, 377 . 379 [RFC7726] Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S. 380 Aldrin, "Clarifying Procedures for Establishing BFD 381 Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726, 382 DOI 10.17487/RFC7726, January 2016, 383 . 385 [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., 386 Aldrin, S., and M. Chen, "Detecting Multiprotocol Label 387 Switched (MPLS) Data-Plane Failures", RFC 8029, 388 DOI 10.17487/RFC8029, March 2017, 389 . 391 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 392 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 393 May 2017, . 395 Appendix A. Acknowledgments 397 The authors greatly appreciate a thorough review and the most helpful 398 comments from Eric Gray and Carlos Pignataro. The authors much 399 appreciate the help of Qian Xin, who provided information about the 400 implementation of this specification. 402 Authors' Addresses 404 Greg Mirsky 405 Ericsson 407 Email: gregimirsky@gmail.com 409 Jeff Tantsura 410 Juniper Networks 412 Email: jefftant.ietf@gmail.com 414 Ilya Varlashkin 415 Google 417 Email: Ilya@nobulus.com 419 Mach(Guoyi) Chen 420 Huawei 422 Email: mach.chen@huawei.com