idnits 2.17.00 (12 Aug 2021) /tmp/idnits33892/draft-ietf-pce-pcep-pmtu-00.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 document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords -- however, there's a paragraph with a matching beginning. Boilerplate error? (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (5 May 2022) is 9 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 PCE Working Group S. Peng 3 Internet-Draft C. Li 4 Intended status: Standards Track Huawei Technologies 5 Expires: 6 November 2022 L. Han 6 China Mobile 7 L. Ndifor 8 MTN Cameroon 9 5 May 2022 11 Support for Path MTU (PMTU) in the Path Computation Element (PCE) 12 communication Protocol (PCEP) 13 draft-ietf-pce-pcep-pmtu-00 15 Abstract 17 The Path Computation Element (PCE) provides path computation 18 functions in support of traffic engineering in Multiprotocol Label 19 Switching (MPLS) and Generalized MPLS (GMPLS) networks. 21 The Source Packet Routing in Networking (SPRING) architecture 22 describes how Segment Routing (SR) can be used to steer packets 23 through an IPv6 or MPLS network using the source routing paradigm. A 24 Segment Routed Path can be derived from a variety of mechanisms, 25 including an IGP Shortest Path Tree (SPT), explicit configuration, or 26 a Path Computation Element (PCE). 28 Since the SR does not require signaling, the path maximum 29 transmission unit (MTU) information for SR path is not available. 30 This document specify the extension to PCE communication protocol 31 (PCEP) to carry path (MTU) in the PCEP messages. 33 Status of This Memo 35 This Internet-Draft is submitted in full conformance with the 36 provisions of BCP 78 and BCP 79. 38 Internet-Drafts are working documents of the Internet Engineering 39 Task Force (IETF). Note that other groups may also distribute 40 working documents as Internet-Drafts. The list of current Internet- 41 Drafts is at https://datatracker.ietf.org/drafts/current/. 43 Internet-Drafts are draft documents valid for a maximum of six months 44 and may be updated, replaced, or obsoleted by other documents at any 45 time. It is inappropriate to use Internet-Drafts as reference 46 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on 6 November 2022. 50 Copyright Notice 52 Copyright (c) 2022 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 57 license-info) in effect on the date of publication of this document. 58 Please review these documents carefully, as they describe your rights 59 and restrictions with respect to this document. Code Components 60 extracted from this document must include Revised BSD License text as 61 described in Section 4.e of the Trust Legal Provisions and are 62 provided without warranty as described in the Revised BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 67 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 68 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 4. PCEP Extention . . . . . . . . . . . . . . . . . . . . . . . 5 70 4.1. Extensions to METRIC Object . . . . . . . . . . . . . . . 5 71 4.2. Multi-Path Handling . . . . . . . . . . . . . . . . . . . 6 72 4.3. Stateful PCE and PCE Initiated LSPs . . . . . . . . . . . 7 73 4.4. Segment Routing . . . . . . . . . . . . . . . . . . . . . 7 74 4.5. Path MTU Adjustment . . . . . . . . . . . . . . . . . . . 7 75 5. Future Plan . . . . . . . . . . . . . . . . . . . . . . . . . 8 76 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 77 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 78 7.1. METRIC Type . . . . . . . . . . . . . . . . . . . . . . . 8 79 8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 8 80 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 81 9.1. Normative References . . . . . . . . . . . . . . . . . . 9 82 9.2. Informative References . . . . . . . . . . . . . . . . . 9 83 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 85 1. Introduction 87 [RFC5440] describes the Path Computation Element (PCE) Communication 88 Protocol (PCEP). PCEP enables the communication between a Path 89 Computation Client (PCC) and a PCE, or between PCE and PCE, for the 90 purpose of computation of Multiprotocol Label Switching (MPLS) as 91 well as Generalzied MPLS (GMPLS) Traffic Engineering Label Switched 92 Path (TE LSP) characteristics. 94 [RFC8231] specifies a set of extensions to PCEP to enable stateful 95 control of TE LSPs within and across PCEP sessions in compliance with 96 [RFC4657]. It includes mechanisms to effect LSP State 97 Synchronization between PCCs and PCEs, delegation of control over 98 LSPs to PCEs, and PCE control of timing and sequence of path 99 computations within and across PCEP sessions. The model of operation 100 where LSPs are initiated from the PCE is described in [RFC8281]. 102 As per [RFC8402], with Segment Routing (SR), a node steers a packet 103 through an ordered list of instructions, called segments. A segment 104 can represent any instruction, topological or service-based. A 105 segment can have a semantic local to an SR node or global within an 106 SR domain. SR allows to enforce a flow through any path and service 107 chain while maintaining per-flow state only at the ingress node of 108 the SR domain. Segments can be derived from different components: 109 IGP, BGP, Services, Contexts, Locators, etc. The SR architecture can 110 be applied to the MPLS forwarding plane without any change, in which 111 case an SR path corresponds to an MPLS Label Switching Path (LSP). 112 The SR is applied to IPV6 forwarding plane using SRH. A SR path can 113 be derived from an IGP Shortest Path Tree (SPT), but SR-TE paths may 114 not follow IGP SPT. Such paths may be chosen by a suitable network 115 planning tool, or a PCE and provisioned on the ingress node. 117 As per [RFC8664], it is possible to use a stateful PCE for computing 118 one or more SR-TE paths taking into account various constraints and 119 objective functions. Once a path is chosen, the stateful PCE can 120 initiate an SR-TE path on a PCC using PCEP extensions specified in 121 [RFC8281] using the SR specific PCEP extensions specified in 122 [RFC8664]. [RFC8664] specifies PCEP extensions for supporting a SR- 123 TE LSP for MPLS data plane. [I-D.ietf-pce-segment-routing-ipv6] 124 extend PCEP to support SR for IPv6 data plane. 126 The maximum transmission unit (MTU) is the largest size packet or 127 frame, in bytes, that can be sent in a network. An MTU that is too 128 large might cause retransmissions. Too small an MTU might cause the 129 router to send and handle relatively more header overhead and 130 acknowledgments. When an LSP is created across a set of links with 131 different MTU sizes, the ingress router need to know what the 132 smallest MTU is on the LSP path. If this MTU is larger than the MTU 133 of one of the intermediate links, traffic might be dropped, because 134 MPLS packets cannot be fragmented. Also, the ingress router may not 135 be aware of this type of traffic loss, because the control plane for 136 the LSP would still function normally. [RFC3209] specify the 137 mechanism of MTU signaling in RSVP. 139 Since the SR does not require signaling, the path MTU information for 140 SR path is not available. This document specify the extension to 141 PCEP to carry path MTU in the PCEP messages. It is assumed that the 142 PCE is aware of the link MTU as part of the Traffic Engineering 143 Database (TED) population. This could be done via IGP, BGP-LS 144 [I-D.ietf-idr-bgp-ls-link-mtu] or some other means. Thus the PCE can 145 find the path MTU at the time of path computation and include this 146 information as part of the PCEP messages. 148 Though the key use case for path MTU is SR, the PCEP extension (as 149 specified in this document) creates a new metric type for path MTU, 150 making this a generic extension that can be used independent of SR. 152 Note that in SR, the term Maximum SID Depth (MSD) [RFC8491] refers to 153 the maximum number of SIDs that an ingress is capable of imposing on 154 a packet. The PMTU on the other hand determines if the IP 155 fragmentation could be avoided. 157 2. Requirements Language 159 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 160 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 161 "OPTIONAL" in this document are to be interpreted as described in BCP 162 14 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they 163 appear in all capitals, as shown here. 165 3. Terminology 167 This draft refers to the terms defined in [RFC8201], [RFC4821] and 168 [RFC3988]. 170 MTU: Maximum Transmission Unit, the size in bytes of the largest IP 171 packet, including the IP header and payload, that can be 172 transmitted on a link or path. Note that this could more properly 173 be called the IP MTU, to be consistent with how other standards 174 organizations use the acronym MTU. 176 Link MTU: The Maximum Transmission Unit, i.e., maximum IP packet 177 size in bytes, that can be conveyed in one piece over a link. Be 178 aware that this definition is different from the definition used 179 by other standards organizations. 181 For IETF documents, link MTU is uniformly defined as the IP MTU 182 over the link. This includes the IP header, but excludes link 183 layer headers and other framing that is not part of IP or the IP 184 payload. 186 Be aware that other standards organizations generally define link 187 MTU to include the link layer headers. 189 For the MPLS data plane, this size includes the IP header and data 190 (or other payload) and the label stack but does not include any 191 lower-layer headers. A link may be an interface (such as Ethernet 192 or Packet-over-SONET), a tunnel (such as GRE or IPsec), or an LSP. 194 Path: The set of links traversed by a packet between a source node 195 and a destination node. 197 Path MTU, or PMTU: The minimum link MTU of all the links in a path 198 between a source node and a destination node. 200 For the MPLS data plane, it is the MTU of an LSP from a given LSR 201 to the egress(es), over each valid (forwarding) path. This size 202 includes the IP header and data (or other payload) and any part of 203 the label stack that was received by the ingress LSR before it 204 placed the packet into the LSP (this part of the label stack is 205 considered part of the payload for this LSP). The size does not 206 include any lower-level headers. 208 4. PCEP Extention 210 4.1. Extensions to METRIC Object 212 The METRIC object is defined in Section 7.8 of [RFC5440], comprising 213 metric-value and metric-type (T field), and a flags field, comprising 214 a number of bit flags (B bit and C bit). This document defines a new 215 type for the METRIC object for Path MTU. 217 * T = TBD: Path MTU. 219 * A network comprises of a set of N links {Li, (i=1...N)}. 221 * A path P of a LSP is a list of K links {Lpi,(i=1...K)}. 223 * A Link MTU of link L is denoted M(L). 225 * A Path MTU metric for the path P = Min {M(Lpi), (i=1...K)}. 227 The Path MTU metric type of the METRIC object in PCEP represents the 228 minimum of the Link MTU of all links along the path. 230 When PCE computes the path, it can also find the Path MTU (based on 231 the above criteria) and include this information in the METRIC object 232 with the above metric type in the PCEP message when replying to the 233 PCC. In a Path Computation Reply (PCRep) message, the PCE MAY insert 234 the METRIC object with an Explicit Route Object (ERO) so as to 235 provide the METRIC (path MTU) for the computed path. The PCE MAY 236 also insert the METRIC object with a NO-PATH object to indicate that 237 the metric constraint could not be satisfied. 239 Further, a PCC MAY use the Path MTU metric in a Path Computation 240 Request (PCReq) message to request a path meeting the MTU requirement 241 of the path. In this case, the B bit MUST be set to suggest a bound 242 (a maximum) for the Path MTU metric that must not be exceeded for the 243 PCC to consider the computed path as acceptable. The Path MTU metric 244 must be less than or equal to the value specified in the metric-value 245 field. 247 A PCC can also use this metric to ask PCE to optimize the path MTU 248 during path computation. In this case, the B bit MUST be cleared. 250 The error handling and processing of the METRIC object is as 251 specified in [RFC5440]. 253 4.2. Multi-Path Handling 255 [I-D.ietf-pce-multipath] extends PCEP to support signaling of 256 multipath information i.e. to all each Candidate-Path to contain 257 multiple Segment-Lists. 259 The PMTU could be supported per segment list as well. The exact 260 mechanism to support this is left for further revision of this 261 document. 263 4.3. Stateful PCE and PCE Initiated LSPs 265 [RFC8231] specifies a set of extensions to PCEP to enable stateful 266 control of MPLS-TE LSPs via PCEP and the maintaining of these LSPs at 267 the stateful PCE. It further distinguishes between an active and a 268 passive stateful PCE. A passive stateful PCE uses LSP state 269 information learned from PCCs to optimize path computations but does 270 not actively update LSP state. In contrast, an active stateful PCE 271 utilizes the LSP delegation mechanism to update LSP parameters in 272 those PCCs that delegated control over their LSPs to the PCE. 273 [RFC8281] describes the setup, maintenance, and teardown of PCE- 274 initiated LSPs under the stateful PCE model. The document defines 275 the PCInitiate message that is used by a PCE to request a PCC to set 276 up a new LSP. 278 The new metric type defined in this document can also be used with 279 the stateful PCE extensions. The format of PCEP messages described 280 in [RFC8231] and [RFC8281] uses and 281 , respectively, (where the 282 is the attribute-list defined in Section 6.5 of [RFC5440]). 284 A PCE MAY include the path MTU metric in PCInitiate or PCUpd message 285 to inform the PCC of the path MTU calculated for the path. A PCC MAY 286 include the path MTU metric as a bound constraint or to indicate 287 optimization criteria (similar to PCReq). 289 4.4. Segment Routing 291 A Segment Routed path (SR path) can be derived from an IGP Shortest 292 Path Tree (SPT). Segment Routed Traffic Engineering paths (SR-TE 293 paths) may not follow IGP SPT. Such paths may be chosen by a 294 suitable network planning tool and provisioned on the source node of 295 the SR-TE path. 297 It is possible to use a PCE for computing one or more SR-TE paths 298 taking into account various constraints and objective functions. 299 Once a path is chosen, the PCE can inform an SR-TE path on a PCC 300 using PCEP extensions specified in [RFC8664]. Further, 301 [I-D.ietf-pce-segment-routing-ipv6] adds the support for IPv6 data 302 plane in SR. 304 The new metric type for path MTU is applicable for the SR-TE path and 305 require no additional extensions. 307 4.5. Path MTU Adjustment 309 The path MTU metric can be used for both primary and protection path. 311 The minimal value of the link MTU along the path is collected, based 312 on which minor adjustment is made to cater for overhead introduced by 313 the protection mechanisms such as TI-LFA. The path MTU is the value 314 of the minimum link MTU minus the overhead. In this way, the ingress 315 node can use the path MTU directly. 317 5. Future Plan 319 A new SPRING document needs to be published and refered by this 320 document. 322 6. Security Considerations 324 This document defines a new METRIC type that do not add any new 325 security concerns beyond those discussed in [RFC5440] in itself. 326 Some deployments may find the path MTU information to be extra 327 sensitive and could be used to influence path computation and setup 328 with adverse effect. Additionally, snooping of PCEP messages with 329 such data or using PCEP messages for network reconnaissance may give 330 an attacker sensitive information about the operations of the 331 network. Thus, such deployment should employ suitable PCEP security 332 mechanisms like TCP Authentication Option (TCP-AO) [RFC5925] or 333 Transport Layer Security (TLS) [RFC8253]. The procedure based on TLS 334 is considered a security enhancement and thus is much better suited 335 for the sensitive information. 337 7. IANA Considerations 339 This document makes following requests to IANA for action. 341 7.1. METRIC Type 343 IANA maintains the "Path Computation Element Protocol (PCEP) Numbers" 344 registry. Within this registry, IANA maintains a subregistry for 345 "METRIC Object T Field". IANA is requested to make the following 346 allocation: 348 Value Description Reference 349 ---------------------- ---------------------------- -------------- 350 TBD Path MTU This document 352 8. Acknowledgement 354 We would like to thank Dhruv Dhody for his contributions for this 355 document. 357 9. References 358 9.1. Normative References 360 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 361 Requirement Levels", BCP 14, RFC 2119, 362 DOI 10.17487/RFC2119, March 1997, 363 . 365 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 366 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 367 DOI 10.17487/RFC5440, March 2009, 368 . 370 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 371 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 372 May 2017, . 374 [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path 375 Computation Element Communication Protocol (PCEP) 376 Extensions for Stateful PCE", RFC 8231, 377 DOI 10.17487/RFC8231, September 2017, 378 . 380 [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path 381 Computation Element Communication Protocol (PCEP) 382 Extensions for PCE-Initiated LSP Setup in a Stateful PCE 383 Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, 384 . 386 9.2. Informative References 388 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 389 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 390 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 391 . 393 [RFC3988] Black, B. and K. Kompella, "Maximum Transmission Unit 394 Signalling Extensions for the Label Distribution 395 Protocol", RFC 3988, DOI 10.17487/RFC3988, January 2005, 396 . 398 [RFC4657] Ash, J., Ed. and J.L. Le Roux, Ed., "Path Computation 399 Element (PCE) Communication Protocol Generic 400 Requirements", RFC 4657, DOI 10.17487/RFC4657, September 401 2006, . 403 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 404 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 405 . 407 [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP 408 Authentication Option", RFC 5925, DOI 10.17487/RFC5925, 409 June 2010, . 411 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 412 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 413 DOI 10.17487/RFC8201, July 2017, 414 . 416 [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody, 417 "PCEPS: Usage of TLS to Provide a Secure Transport for the 418 Path Computation Element Communication Protocol (PCEP)", 419 RFC 8253, DOI 10.17487/RFC8253, October 2017, 420 . 422 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 423 Decraene, B., Litkowski, S., and R. Shakir, "Segment 424 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 425 July 2018, . 427 [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, 428 "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, 429 DOI 10.17487/RFC8491, November 2018, 430 . 432 [RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 433 and J. Hardwick, "Path Computation Element Communication 434 Protocol (PCEP) Extensions for Segment Routing", RFC 8664, 435 DOI 10.17487/RFC8664, December 2019, 436 . 438 [I-D.ietf-pce-multipath] 439 Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P., 440 Bidgoli, H., Yadav, B., Peng, S., and G. Mishra, "PCEP 441 Extensions for Signaling Multipath Information", Work in 442 Progress, Internet-Draft, draft-ietf-pce-multipath-05, 30 443 March 2022, . 446 [I-D.ietf-pce-segment-routing-ipv6] 447 Li, C., Negi, M., Sivabalan, S., Koldychev, M., 448 Kaladharan, P., and Y. Zhu, "PCEP Extensions for Segment 449 Routing leveraging the IPv6 data plane", Work in Progress, 450 Internet-Draft, draft-ietf-pce-segment-routing-ipv6-13, 1 451 April 2022, . 454 [I-D.ietf-idr-bgp-ls-link-mtu] 455 Zhu, Y., Hu, Z., Peng, S., and R. Mwehaire, "Signaling 456 Maximum Transmission Unit (MTU) using BGP-LS", Work in 457 Progress, Internet-Draft, draft-ietf-idr-bgp-ls-link-mtu- 458 02, 26 November 2021, . 461 Authors' Addresses 463 Shuping Peng 464 Huawei Technologies 465 Huawei Campus, No. 156 Beiqing Rd. 466 Beijing 467 100095 468 China 469 Email: pengshuping@huawei.com 471 Cheng Li 472 Huawei Technologies 473 Huawei Campus, No. 156 Beiqing Rd. 474 Beijing 475 100095 476 China 477 Email: c.l@huawei.com 479 Liuyan Han 480 China Mobile 481 Beijing 482 100053 483 China 484 Email: hanliuyan@chinamobile.com 486 Luc-Fabrice Ndifor 487 MTN Cameroon 488 Cameroon 489 Email: Luc-Fabrice.Ndifor@mtn.com