idnits 2.17.1 draft-ietf-mpls-bfd-directed-09.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (August 21, 2018) is 2076 days in the past. Is this intentional? 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, 2019 Nuage Networks 6 I. Varlashkin 7 Google 8 M. Chen 9 Huawei 10 August 21, 2018 12 Bidirectional Forwarding Detection (BFD) Directed Return Path 13 draft-ietf-mpls-bfd-directed-09 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, 2019. 40 Copyright Notice 42 Copyright (c) 2018 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. Static and RSVP-TE sub-TLVs . . . . . . . . . . . . . . . 4 64 3.3. Return Codes . . . . . . . . . . . . . . . . . . . . . . 5 65 4. Use Case Scenario . . . . . . . . . . . . . . . . . . . . . . 5 66 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 67 5.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 6 68 5.2. Return Code . . . . . . . . . . . . . . . . . . . . . . . 6 69 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 70 7. Normative References . . . . . . . . . . . . . . . . . . . . 6 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 contributes to producing false positive defect 88 notifications, i.e., false alarms, at the ingress BFD peer. 90 This document defines the BFD Reverse Path TLV as an extension to LSP 91 Ping [RFC8029] and proposes that it is to be used to instruct the 92 egress BFD peer to use an explicit path for its BFD control packets 93 associated with a particular BFD session. The TLV will be allocated 94 from the TLV and sub-TLV registry defined in [RFC8029]. As a special 95 case, forward and reverse directions of the BFD session can form a 96 bi-directional co-routed associated channel. 98 1.1. Conventions used in this document 100 1.1.1. Requirements Language 102 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 103 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 104 "OPTIONAL" in this document are to be interpreted as described in BCP 105 14 [RFC2119] [RFC8174] when, and only when, they appear in all 106 capitals, as shown here. 108 2. Problem Statement 110 When BFD is used to monitor explicitly routed unidirectional path, 111 e.g., MPLS-TE LSP, BFD control packets in forward direction would be 112 in-band using the mechanism defined in [RFC5884] and [RFC5586]. But 113 the reverse direction of the BFD session would follow the shortest 114 path route and that might lead to the problem in detecting failures 115 on an explicit unidirectional path as described below: 117 o a failure detection by ingress node on the reverse path cannot be 118 interpreted as bi-directional failure unambiguously and thus 119 trigger, for example, protection switchover of the forward 120 direction without the possibility of being a false positive. 122 To address this scenario, the egress BFD peer would be instructed to 123 use a specific path for BFD control packets. 125 3. Control of the Reverse BFD Path 127 To bootstrap a BFD session over an MPLS LSP, LSP ping, defined in 128 [RFC8029], MUST be used with BFD Discriminator TLV [RFC5884]. This 129 document defines a new TLV, BFD Reverse Path TLV, that MUST contain a 130 single sub-TLV that can be used to carry information about the 131 reverse path for the BFD session that is specified by the value in 132 BFD Discriminator TLV. 134 3.1. BFD Reverse Path TLV 136 The BFD Reverse Path TLV is an optional TLV within the LSP ping 137 [RFC8029]. However, if used, the BFD Discriminator TLV MUST be 138 included in an Echo Request message as well. If the BFD 139 Discriminator TLV is not present when the BFD Reverse Path TLV is 140 included; then it MUST be treated as malformed Echo Request, as 141 described in [RFC8029]. 143 The BFD Reverse Path TLV carries information about the path onto 144 which the egress BFD peer of the BFD session referenced by the BFD 145 Discriminator TLV MUST transmit BFD control packets. The format of 146 the BFD Reverse Path TLV is as presented in Figure 1. 148 0 1 2 3 149 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 1 150 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 151 | BFD Reverse Path TLV Type | Length | 152 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 153 | Reverse Path | 154 ~ ~ 155 | | 156 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 158 Figure 1: BFD Reverse Path TLV 160 BFD Reverse Path TLV Type is two octets in length and has a value of 161 TBD1 (to be assigned by IANA as requested in Section 5). 163 Length field is two octets long and defines the length in octets of 164 the Reverse Path field. 166 Reverse Path field contains a sub-TLV. Any non-multicast Target FEC 167 Stack sub-TLV (already defined, or to be defined in the future) for 168 TLV Types 1, 16, and 21 of MPLS LSP Ping Parameters registry MAY be 169 used in this field. Multicast Target FEC Stack sub-TLVs, i.e., p2mp 170 and mp2mp, SHOULD NOT be included in Reverse Path field. If the 171 egress LSR finds multicast Target Stack sub-TLV, it MUST send echo 172 reply with the received Reverse Path TLV, BFD Discriminator TLV and 173 set the Return Code to "Inappropriate Target FEC Stack sub-TLV 174 present" Section 3.3. None, one or more sub-TLVs MAY be included in 175 the BFD Reverse Path TLV. If no sub-TLVs are found in the BFD 176 Reverse Path TLV, the egress BFD peer MUST revert to using the local 177 policy based decision as described in Section 7 [RFC5884], i.e., 178 routed over IP network. 180 If the egress LSR cannot find the path specified in the Reverse Path 181 TLV it MUST send Echo Reply with the received BFD Discriminator TLV, 182 Reverse Path TLV and set the Return Code to "Failed to establish the 183 BFD session. The specified reverse path was not found" Section 3.3. 184 The egress BFD peer MAY establish the BFD session over IP network as 185 defined in [RFC5884]. 187 3.2. Static and RSVP-TE sub-TLVs 189 When an explicit path on an MPLS data plane is set either as Static 190 or RSVP-TE LSP, corresponding sub-TLVs, defined in [RFC7110], MAY be 191 used to identify the explicit reverse path for the BFD session. If 192 any of defined in [RFC7110] sub-TLVs used in BFD Reverse Path TLV, 193 then the periodic verification of the control plane against the data 194 plane, as recommended in Section 3.2 [RFC5884], MUST use the Return 195 Path TLV, as per [RFC7110], with that sub-TLV. By using the LSP Ping 196 with Return Path TLV an operator will be able to verify that the 197 forward LSP and the reverse LSP are mapped to the same FECs as BFD 198 session both at the ingress and the egress systems. 200 3.3. Return Codes 202 This document defines the following Return Codes for MPLS LSP Echo 203 Reply: 205 o "Inappropriate Target FEC Stack sub-TLV present", (TBD3). When 206 multicast Target FEC Stack sub-TLV found in the received Echo 207 Request by the egress BFD peer, an Echo Reply with the return code 208 set to "Inappropriate Target FEC Stack sub-TLV present" MUST be 209 sent to the ingress BFD peer Section 3.1. 211 o "Failed to establish the BFD session. The specified reverse path 212 was not found", (TBD4). When a specified reverse path is not 213 available at the egress BFD peer, an Echo Reply with the return 214 code set to "Failed to establish the BFD session. The specified 215 reverse path was not found" MUST be sent back to the ingress BFD 216 peer Section 3.1. 218 4. Use Case Scenario 220 In the network presented in Figure 2 node A monitors two tunnels to 221 node H: A-B-C-D-G-H and A-B-E-F-G-H. To bootstrap a BFD session to 222 monitor the first tunnel, node A MUST include a BFD Discriminator TLV 223 with Discriminator value (e.g., foobar-1) and MAY include a BFD 224 Reverse Path TLV that references H-G-D-C-B-A tunnel. To bootstrap a 225 BFD session to monitor the second tunnel, node A MUST include a BFD 226 Discriminator TLV with a different Discriminator value (e.g., foobar- 227 2) [RFC7726] and MAY include a BFD Reverse Path TLV that references 228 H-G-F-E-B-A tunnel. 230 C---------D 231 | | 232 A-------B G-----H 233 | | 234 E---------F 236 Figure 2: Use Case for BFD Reverse Path TLV 238 If an operator needs node H to monitor a path to node A, e.g. 239 H-G-D-C-B-A tunnel, then by looking up the list of known Reverse 240 Paths it MAY find and use the existing BFD session. 242 5. IANA Considerations 244 5.1. BFD Reverse Path TLV 246 The IANA is requested to assign a new value for BFD Reverse Path TLV 247 from the "Multiprotocol Label Switching Architecture (MPLS) Label 248 Switched Paths (LSPs) Ping Parameters - TLVs" registry, "TLVs and 249 sub-TLVs" sub-registry. 251 +--------+----------------------+---------------+ 252 | Value | Description | Reference | 253 +--------+----------------------+---------------+ 254 | (TBD1) | BFD Reverse Path TLV | This document | 255 +--------+----------------------+---------------+ 257 Table 1: New BFD Reverse Type TLV 259 5.2. Return Code 261 The IANA is requested to assign a new Return Code value from the 262 "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) 263 Ping Parameters" registry, "Return Codes" sub-registry, as follows 264 using a Standards Action value. 266 +--------+------------------------------------------+---------------+ 267 | Value | Description | Reference | 268 +--------+------------------------------------------+---------------+ 269 | (TBD3) | Inappropriate Target FEC Stack sub-TLV | This document | 270 | | present. | | 271 | (TBD4) | Failed to establish the BFD session. The | This document | 272 | | specified reverse path was not found. | | 273 +--------+------------------------------------------+---------------+ 275 Table 2: New Return Code 277 6. Security Considerations 279 Security considerations discussed in [RFC5880], [RFC5884], [RFC7726], 280 and [RFC8029], apply to this document. 282 7. Normative References 284 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 285 Requirement Levels", BCP 14, RFC 2119, 286 DOI 10.17487/RFC2119, March 1997, 287 . 289 [RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., 290 "MPLS Generic Associated Channel", RFC 5586, 291 DOI 10.17487/RFC5586, June 2009, 292 . 294 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 295 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 296 . 298 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 299 (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, 300 DOI 10.17487/RFC5881, June 2010, 301 . 303 [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 304 (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883, 305 June 2010, . 307 [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, 308 "Bidirectional Forwarding Detection (BFD) for MPLS Label 309 Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884, 310 June 2010, . 312 [RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord, 313 "Return Path Specified Label Switched Path (LSP) Ping", 314 RFC 7110, DOI 10.17487/RFC7110, January 2014, 315 . 317 [RFC7726] Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S. 318 Aldrin, "Clarifying Procedures for Establishing BFD 319 Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726, 320 DOI 10.17487/RFC7726, January 2016, 321 . 323 [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., 324 Aldrin, S., and M. Chen, "Detecting Multiprotocol Label 325 Switched (MPLS) Data-Plane Failures", RFC 8029, 326 DOI 10.17487/RFC8029, March 2017, 327 . 329 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 330 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 331 May 2017, . 333 Appendix A. Acknowledgments 335 Authors greatly appreciate thorough review and the most helpful 336 comments from Eric Gray and Carlos Pignataro. 338 Authors' Addresses 340 Greg Mirsky 341 ZTE 343 Email: gregimirsky@gmail.com 345 Jeff Tantsura 346 Nuage Networks 348 Email: jefftant.ietf@gmail.com 350 Ilya Varlashkin 351 Google 353 Email: Ilya@nobulus.com 355 Mach(Guoyi) Chen 356 Huawei 358 Email: mach.chen@huawei.com