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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 ZTE 4 Intended status: Standards Track J. Tantsura 5 Expires: 21 February 2022 Juniper Networks 6 I. Varlashkin 7 Google 8 M. Chen 9 Huawei 10 20 August 2021 12 Bidirectional Forwarding Detection (BFD) Directed Return Path for MPLS 13 Label Switched Paths (LSPs) 14 draft-ietf-mpls-bfd-directed-18 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 21 February 2022. 41 Copyright Notice 43 Copyright (c) 2021 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 Simplified BSD License text 52 as described in Section 4.e of the Trust Legal Provisions and are 53 provided without warranty as described in the Simplified 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 3.2. Return Codes 194 This document defines the following Return Codes for MPLS LSP Echo 195 Reply: 197 * "Inappropriate Target FEC Stack sub-TLV present", (TBD3). When 198 multicast Target FEC Stack sub-TLV found in the received Echo 199 Request by the egress BFD peer, an Echo Reply with the return code 200 set to "Inappropriate Target FEC Stack sub-TLV present" MUST be 201 sent to the ingress BFD peer Section 3.1. 203 * "Failed to establish the BFD session. The specified reverse path 204 was not found", (TBD4). When a specified reverse path is not 205 available at the egress BFD peer, an Echo Reply with the return 206 code set to "Failed to establish the BFD session. The specified 207 reverse path was not found" MUST be sent back to the ingress BFD 208 peer Section 3.1. 210 4. Use Case Scenario 212 In the network presented in Figure 2 node A monitors two tunnels to 213 node H: A-B-C-D-G-H and A-B-E-F-G-H. To bootstrap a BFD session to 214 monitor the first tunnel, node A MUST include a BFD Discriminator TLV 215 with Discriminator value (e.g., foobar-1) and MAY include a BFD 216 Reverse Path TLV that references H-G-D-C-B-A tunnel. To bootstrap a 217 BFD session to monitor the second tunnel, node A MUST include a BFD 218 Discriminator TLV with a different Discriminator value (e.g., foobar- 219 2) [RFC7726] and MAY include a BFD Reverse Path TLV that references 220 H-G-F-E-B-A tunnel. 222 C---------D 223 | | 224 A-------B G-----H 225 | | 226 E---------F 228 Figure 2: Use Case for BFD Reverse Path TLV 230 If an operator needs node H to monitor a path to node A, e.g. 231 H-G-D-C-B-A tunnel, then by looking up the list of known Reverse 232 Paths it MAY find and use the existing BFD session. 234 5. Operational Considerations 236 When an explicit path is set either as Static or RSVP-TE LSP, 237 corresponding sub-TLVs, defined in [RFC7110], MAY be used to identify 238 the explicit reverse path for the BFD session. If any of defined in 239 [RFC7110] sub-TLVs used in BFD Reverse Path TLV, then the periodic 240 verification of the control plane against the data plane, as 241 recommended in Section 4 [RFC5884], MUST use the Return Path TLV, as 242 per [RFC7110], with that sub-TLV. By using the LSP Ping with Return 243 Path TLV, an operator monitors whether at the egress BFD node the 244 reverse LSP is mapped to the same FEC as the BFD session. Selection 245 and control of the rate of LSP Ping with Return Path TLV follows the 246 recommendation of [RFC5884]: "The rate of generation of these LSP 247 Ping Echo request messages SHOULD be significantly less than the rate 248 of generation of the BFD Control packets. An implementation MAY 249 provide configuration options to control the rate of generation of 250 the periodic LSP Ping Echo request messages." 252 Suppose an operator planned network maintenance activity that 253 possibly affects FEC used in the BFD Reverse Path TLV. In that case, 254 the operator MUST avoid the unnecessary disruption using the LSP Ping 255 with a new FEC in the BFD Reverse Path TLV. But in some scenarios, 256 proactive measures cannot be taken. Because the frequency of LSP 257 Ping messages will be lower than the defect detection time provided 258 by the BFD session. As a result, a change in the reverse-path FEC 259 will first be detected as the BFD session's failure. In such a case, 260 the ingress BFD node SHOULD immediately transmit the LSP Ping Echo 261 request with Return Path TLV to verify whether the FEC is still 262 valid. If the failure was caused by the change in the FEC used for 263 the reverse direction of the BFD session, the ingress BFD node SHOULD 264 bootstrap a new BFD session using another FEC in BFD Reverse Path 265 TLV. 267 6. IANA Considerations 269 6.1. BFD Reverse Path TLV 271 The IANA is requested to assign a new value for BFD Reverse Path TLV 272 from the "Multiprotocol Label Switching Architecture (MPLS) Label 273 Switched Paths (LSPs) Ping Parameters - TLVs" registry, "TLVs and 274 sub-TLVs" sub-registry. 276 +=========+======================+===============+ 277 | Value | Description | Reference | 278 +=========+======================+===============+ 279 | (TBD1) | BFD Reverse Path TLV | This document | 280 +---------+----------------------+---------------+ 282 Table 1: New BFD Reverse Type TLV 284 6.2. Return Code 286 The IANA is requested to assign a new Return Code value from the 287 "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) 288 Ping Parameters" registry, "Return Codes" sub-registry, as follows 289 using a Standards Action value. 291 +=========+=============================+===============+ 292 | Value | Description | Reference | 293 +=========+=============================+===============+ 294 | (TBD3) | Inappropriate Target FEC | This document | 295 | | Stack sub-TLV present. | | 296 +---------+-----------------------------+---------------+ 297 | (TBD4) | Failed to establish the BFD | This document | 298 | | session. The specified | | 299 | | reverse path was not found. | | 300 +---------+-----------------------------+---------------+ 302 Table 2: New Return Code 304 7. Implementation Status 306 - The organization responsible for the implementation: ZTE 307 Corporation. 309 - The implementation's name ROSng empowers traditional routers, e.g., 310 ZXCTN 6000. 312 - A brief general description: A Return Path can be specified for a 313 BFD session over RSVP tunnel or LSP. The same can be specified for a 314 backup RSVP tunnel/LSP. 316 The implementation's level of maturity: production. 318 - Coverage: RSVP LSP (no support for Static LSP) 320 - Version compatibility: draft-ietf-mpls-bfd-directed-10. 322 - Licensing: proprietary. 324 - Implementation experience: simple once you support RFC 7110. 326 - Contact information: Qian Xin qian.xin2@zte.com.cn 328 - The date when information about this particular implementation was 329 last updated: 12/16/2019 331 Note to RFC Editor: This section MUST be removed before publication 332 of the document. 334 8. Security Considerations 336 Security considerations discussed in [RFC5880], [RFC5884], [RFC7726], 337 [RFC8029], and [RFC7110] apply to this document. 339 9. Normative References 341 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 342 Requirement Levels", BCP 14, RFC 2119, 343 DOI 10.17487/RFC2119, March 1997, 344 . 346 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 347 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 348 . 350 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 351 (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, 352 DOI 10.17487/RFC5881, June 2010, 353 . 355 [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 356 (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883, 357 June 2010, . 359 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 360 "Bidirectional Forwarding Detection (BFD) for MPLS Label 361 Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884, 362 June 2010, . 364 [RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord, 365 "Return Path Specified Label Switched Path (LSP) Ping", 366 RFC 7110, DOI 10.17487/RFC7110, January 2014, 367 . 369 [RFC7726] Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S. 370 Aldrin, "Clarifying Procedures for Establishing BFD 371 Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726, 372 DOI 10.17487/RFC7726, January 2016, 373 . 375 [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., 376 Aldrin, S., and M. Chen, "Detecting Multiprotocol Label 377 Switched (MPLS) Data-Plane Failures", RFC 8029, 378 DOI 10.17487/RFC8029, March 2017, 379 . 381 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 382 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 383 May 2017, . 385 Appendix A. Acknowledgments 387 The authors greatly appreciate a thorough review and the most helpful 388 comments from Eric Gray and Carlos Pignataro. The authors much 389 appreciate the help of Qian Xin, who provided information about the 390 implementation of this specification. 392 Authors' Addresses 394 Greg Mirsky 395 ZTE 397 Email: gregimirsky@gmail.com, gregory.mirsky@ztetx.com 399 Jeff Tantsura 400 Juniper Networks 402 Email: jefftant.ietf@gmail.com 404 Ilya Varlashkin 405 Google 407 Email: Ilya@nobulus.com 409 Mach(Guoyi) Chen 410 Huawei 412 Email: mach.chen@huawei.com