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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: February 22, 2020 Nuage Networks 6 I. Varlashkin 7 Google 8 M. Chen 9 Huawei 10 August 21, 2019 12 Bidirectional Forwarding Detection (BFD) Directed Return Path 13 draft-ietf-mpls-bfd-directed-12 15 Abstract 17 Bidirectional Forwarding Detection (BFD) is expected to be able to 18 monitor a wide variety of encapsulations of paths between systems. 19 When a BFD session monitors an explicitly routed unidirectional path 20 there may be a need to direct egress BFD peer to use a specific path 21 for the reverse direction of the BFD session. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at https://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on February 22, 2020. 40 Copyright Notice 42 Copyright (c) 2019 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (https://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 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 . . . . . . . . . . . . . . . . . 5 66 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 67 6.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 6 68 6.2. Return Code . . . . . . . . . . . . . . . . . . . . . . . 6 69 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 70 8. Normative References . . . . . . . . . . . . . . . . . . . . 7 71 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 8 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 74 1. Introduction 76 [RFC5880], [RFC5881], and [RFC5883] established the BFD protocol for 77 IP networks. [RFC5884] and [RFC7726] set rules for using BFD 78 asynchronous mode over IP/MPLS LSPs. These standards do not define 79 means to control the path selection at the egress BFD peer to send 80 BFD control packets towards the ingress BFD system. 82 For the case when BFD is used to detect defects of the traffic 83 engineered LSP the path the BFD control packets transmitted by the 84 egress BFD system toward the ingress may be disjoint from the LSP in 85 the forward direction. The fact that BFD control packets are not 86 guaranteed to follow the same links and nodes in both forward and 87 reverse directions may be one of the factors contributing to 88 producing false positive defect notifications, i.e., false alarms, at 89 the ingress BFD peer. Ensuring that both directions of the BFD 90 session use co-routed paths may, in some environments, improve the 91 determinism of the failure detection and localization. 93 This document defines the BFD Reverse Path TLV as an extension to LSP 94 Ping [RFC8029] and proposes that it is to be used to instruct the 95 egress BFD peer to use an explicit path for its BFD control packets 96 associated with a particular BFD session. The TLV will be allocated 97 from the TLV and sub-TLV registry defined in [RFC8029]. As a special 98 case, forward and reverse directions of the BFD session can form a 99 bi-directional co-routed associated channel. 101 1.1. Conventions used in this document 103 1.1.1. Requirements Language 105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 107 "OPTIONAL" in this document are to be interpreted as described in BCP 108 14 [RFC2119] [RFC8174] when, and only when, they appear in all 109 capitals, as shown here. 111 2. Problem Statement 113 When BFD is used to monitor explicitly routed unidirectional path, 114 e.g., MPLS-TE LSP, BFD control packets in forward direction would be 115 in-band using the mechanism defined in [RFC5884]. But the reverse 116 direction of the BFD session would follow the shortest path route and 117 that might lead to the problem in detecting failures on an explicit 118 unidirectional path as described below: 120 o detection by an ingress node of a failure on the reverse path may 121 not be unambiguously interpreted as the failure of the path in the 122 forward direction. 124 To address this scenario, the egress BFD peer would be instructed to 125 use a specific path for BFD control packets. 127 3. Control of the Reverse BFD Path 129 To bootstrap a BFD session over an MPLS LSP, LSP ping, defined in 130 [RFC8029], MUST be used with BFD Discriminator TLV [RFC5884]. This 131 document defines a new TLV, BFD Reverse Path TLV, that MUST contain a 132 single sub-TLV that can be used to carry information about the 133 reverse path for the BFD session that is specified by the value in 134 BFD Discriminator TLV. 136 3.1. BFD Reverse Path TLV 138 The BFD Reverse Path TLV is an optional TLV within the LSP ping 139 [RFC8029]. However, if used, the BFD Discriminator TLV MUST be 140 included in an Echo Request message as well. If the BFD 141 Discriminator TLV is not present when the BFD Reverse Path TLV is 142 included; then it MUST be treated as malformed Echo Request, as 143 described in [RFC8029]. 145 The BFD Reverse Path TLV carries information about the path onto 146 which the egress BFD peer of the BFD session referenced by the BFD 147 Discriminator TLV MUST transmit BFD control packets. The format of 148 the BFD Reverse Path TLV is as presented in Figure 1. 150 0 1 2 3 151 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 1 152 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 153 | BFD Reverse Path TLV Type | Length | 154 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 155 | Reverse Path | 156 ~ ~ 157 | | 158 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 160 Figure 1: BFD Reverse Path TLV 162 BFD Reverse Path TLV Type is two octets in length and has a value of 163 TBD1 (to be assigned by IANA as requested in Section 6). 165 Length field is two octets long and defines the length in octets of 166 the Reverse Path field. 168 Reverse Path field contains a sub-TLV. Any non-multicast Target FEC 169 Stack sub-TLV (already defined, or to be defined in the future) for 170 TLV Types 1, 16, and 21 of MPLS LSP Ping Parameters registry MAY be 171 used in this field. Multicast Target FEC Stack sub-TLVs, i.e., p2mp 172 and mp2mp, SHOULD NOT be included in Reverse Path field. If the 173 egress LSR finds multicast Target Stack sub-TLV, it MUST send echo 174 reply with the received Reverse Path TLV, BFD Discriminator TLV and 175 set the Return Code to "Inappropriate Target FEC Stack sub-TLV 176 present" Section 3.2. None, one or more sub-TLVs MAY be included in 177 the BFD Reverse Path TLV. If no sub-TLVs are found in the BFD 178 Reverse Path TLV, the egress BFD peer MUST revert to using the local 179 policy based decision as described in Section 7 [RFC5884], i.e., 180 routed over IP network. 182 If the egress LSR cannot find the path specified in the Reverse Path 183 TLV it MUST send Echo Reply with the received BFD Discriminator TLV, 184 Reverse Path TLV and set the Return Code to "Failed to establish the 185 BFD session. The specified reverse path was not found" Section 3.2. 186 An implementation MAY provide configuration options to define action 187 at the egress BFD peer. For example, if the egress LSR cannot find 188 the path specified in the Reverse Path TLV it MAY establish the BFD 189 session over IP network as defined in [RFC5884]. 191 3.2. Return Codes 193 This document defines the following Return Codes for MPLS LSP Echo 194 Reply: 196 o "Inappropriate Target FEC Stack sub-TLV present", (TBD3). When 197 multicast Target FEC Stack sub-TLV found in the received Echo 198 Request by the egress BFD peer, an Echo Reply with the return code 199 set to "Inappropriate Target FEC Stack sub-TLV present" MUST be 200 sent to the ingress BFD peer Section 3.1. 202 o "Failed to establish the BFD session. The specified reverse path 203 was not found", (TBD4). When a specified reverse path is not 204 available at the egress BFD peer, an Echo Reply with the return 205 code set to "Failed to establish the BFD session. The specified 206 reverse path was not found" MUST be sent back to the ingress BFD 207 peer Section 3.1. 209 4. Use Case Scenario 211 In the network presented in Figure 2 node A monitors two tunnels to 212 node H: A-B-C-D-G-H and A-B-E-F-G-H. To bootstrap a BFD session to 213 monitor the first tunnel, node A MUST include a BFD Discriminator TLV 214 with Discriminator value (e.g., foobar-1) and MAY include a BFD 215 Reverse Path TLV that references H-G-D-C-B-A tunnel. To bootstrap a 216 BFD session to monitor the second tunnel, node A MUST include a BFD 217 Discriminator TLV with a different Discriminator value (e.g., foobar- 218 2) [RFC7726] and MAY include a BFD Reverse Path TLV that references 219 H-G-F-E-B-A tunnel. 221 C---------D 222 | | 223 A-------B G-----H 224 | | 225 E---------F 227 Figure 2: Use Case for BFD Reverse Path TLV 229 If an operator needs node H to monitor a path to node A, e.g. 230 H-G-D-C-B-A tunnel, then by looking up the list of known Reverse 231 Paths it MAY find and use the existing BFD session. 233 5. Operational Considerations 235 When an explicit path is set either as Static or RSVP-TE LSP, 236 corresponding sub-TLVs, defined in [RFC7110], MAY be used to identify 237 the explicit reverse path for the BFD session. If any of defined in 238 [RFC7110] sub-TLVs used in BFD Reverse Path TLV, then the periodic 239 verification of the control plane against the data plane, as 240 recommended in Section 4 [RFC5884], MUST use the Return Path TLV, as 241 per [RFC7110], with that sub-TLV. By using the LSP Ping with Return 242 Path TLV, an operator monitors whether at the egress BFD node the 243 reverse LSP is mapped to the same FEC as the BFD session. Selection 244 and control of the rate of LSP Ping with Return Path TLV follows the 245 recommendation of [RFC5884]: "The rate of generation of these LSP 246 Ping Echo request messages SHOULD be significantly less than the rate 247 of generation of the BFD Control packets. An implementation MAY 248 provide configuration options to control the rate of generation of 249 the periodic LSP Ping Echo request messages." 251 If an operator planned network maintenance activity that possibly 252 affects FEC used in the BFD Reverse Path TLV, the operator MUST avoid 253 the unnecessary disruption using the LSP Ping with a new FEC in the 254 BFD Reverse Path TLV. But in some scenarios, proactive measures 255 cannot be taken. Because the frequency of LSP Ping messages will be 256 lower than the defect detection time provided by the BFD session. As 257 a result, a change in the reverse-path FEC will first be detected as 258 the failure of the BFD session. In such a case, the ingress BFD node 259 SHOULD immediately transmit the LSP Ping Echo request with Return 260 Path TLV to verify whether the FEC is still valid. If the failure 261 was caused by the change in the FEC used for the reverse direction of 262 the BFD session, the ingress BFD node SHOULD bootstrap a new BFD 263 session using another FEC in BFD Reverse Path TLV. 265 6. IANA Considerations 267 6.1. BFD Reverse Path TLV 269 The IANA is requested to assign a new value for BFD Reverse Path TLV 270 from the "Multiprotocol Label Switching Architecture (MPLS) Label 271 Switched Paths (LSPs) Ping Parameters - TLVs" registry, "TLVs and 272 sub-TLVs" sub-registry. 274 +--------+----------------------+---------------+ 275 | Value | Description | Reference | 276 +--------+----------------------+---------------+ 277 | (TBD1) | BFD Reverse Path TLV | This document | 278 +--------+----------------------+---------------+ 280 Table 1: New BFD Reverse Type TLV 282 6.2. Return Code 284 The IANA is requested to assign a new Return Code value from the 285 "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) 286 Ping Parameters" registry, "Return Codes" sub-registry, as follows 287 using a Standards Action value. 289 +--------+----------------------------------------------+-----------+ 290 | Value | Description | Reference | 291 +--------+----------------------------------------------+-----------+ 292 | (TBD3) | Inappropriate Target FEC Stack sub-TLV | This | 293 | | present. | document | 294 | (TBD4) | Failed to establish the BFD session. The | This | 295 | | specified reverse path was not found. | document | 296 +--------+----------------------------------------------+-----------+ 298 Table 2: New Return Code 300 7. Security Considerations 302 Security considerations discussed in [RFC5880], [RFC5884], [RFC7726], 303 and [RFC8029], apply to this document. 305 8. Normative References 307 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 308 Requirement Levels", BCP 14, RFC 2119, 309 DOI 10.17487/RFC2119, March 1997, 310 . 312 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 313 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 314 . 316 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 317 (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, 318 DOI 10.17487/RFC5881, June 2010, 319 . 321 [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 322 (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883, 323 June 2010, . 325 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 326 "Bidirectional Forwarding Detection (BFD) for MPLS Label 327 Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884, 328 June 2010, . 330 [RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord, 331 "Return Path Specified Label Switched Path (LSP) Ping", 332 RFC 7110, DOI 10.17487/RFC7110, January 2014, 333 . 335 [RFC7726] Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S. 336 Aldrin, "Clarifying Procedures for Establishing BFD 337 Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726, 338 DOI 10.17487/RFC7726, January 2016, 339 . 341 [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., 342 Aldrin, S., and M. Chen, "Detecting Multiprotocol Label 343 Switched (MPLS) Data-Plane Failures", RFC 8029, 344 DOI 10.17487/RFC8029, March 2017, 345 . 347 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 348 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 349 May 2017, . 351 Appendix A. Acknowledgments 353 Authors greatly appreciate thorough review and the most helpful 354 comments from Eric Gray and Carlos Pignataro. 356 Authors' Addresses 358 Greg Mirsky 359 ZTE 361 Email: gregimirsky@gmail.com 363 Jeff Tantsura 364 Nuage Networks 366 Email: jefftant.ietf@gmail.com 368 Ilya Varlashkin 369 Google 371 Email: Ilya@nobulus.com 373 Mach(Guoyi) Chen 374 Huawei 376 Email: mach.chen@huawei.com