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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) == Missing Reference: 'RFC8201' is mentioned on line 160, but not defined == Missing Reference: 'RFC4821' is mentioned on line 160, but not defined == Missing Reference: 'RFC3988' is mentioned on line 161, but not defined == Outdated reference: A later version (-25) exists of draft-ietf-pce-segment-routing-ipv6-06 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--).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: May 4, 2021 L. Han 6 China Mobile 7 L. Ndifor 8 MTN Cameroon 9 October 31, 2020 11 Support for Path MTU (PMTU) in the Path Computation Element (PCE) 12 communication Protocol (PCEP). 13 draft-li-pce-pcep-pmtu-03 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 Requirements Language 35 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 36 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 37 "OPTIONAL" in this document are to be interpreted as described in BCP 38 14 [RFC2119] [RFC8174] when, and only when, they appear in all 39 capitals, as shown here. 41 Status of This Memo 43 This Internet-Draft is submitted in full conformance with the 44 provisions of BCP 78 and BCP 79. 46 Internet-Drafts are working documents of the Internet Engineering 47 Task Force (IETF). Note that other groups may also distribute 48 working documents as Internet-Drafts. The list of current Internet- 49 Drafts is at https://datatracker.ietf.org/drafts/current/. 51 Internet-Drafts are draft documents valid for a maximum of six months 52 and may be updated, replaced, or obsoleted by other documents at any 53 time. It is inappropriate to use Internet-Drafts as reference 54 material or to cite them other than as "work in progress." 56 This Internet-Draft will expire on May 4, 2021. 58 Copyright Notice 60 Copyright (c) 2020 IETF Trust and the persons identified as the 61 document authors. All rights reserved. 63 This document is subject to BCP 78 and the IETF Trust's Legal 64 Provisions Relating to IETF Documents 65 (https://trustee.ietf.org/license-info) in effect on the date of 66 publication of this document. Please review these documents 67 carefully, as they describe your rights and restrictions with respect 68 to this document. Code Components extracted from this document must 69 include Simplified BSD License text as described in Section 4.e of 70 the Trust Legal Provisions and are provided without warranty as 71 described in the Simplified BSD License. 73 Table of Contents 75 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 76 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 77 3. PCEP Extention . . . . . . . . . . . . . . . . . . . . . . . 5 78 3.1. Extensions to METRIC Object . . . . . . . . . . . . . . . 5 79 3.2. Stateful PCE and PCE Initiated LSPs . . . . . . . . . . . 6 80 3.3. Segment Routing . . . . . . . . . . . . . . . . . . . . . 7 81 3.4. Path MTU Adjustment . . . . . . . . . . . . . . . . . . . 7 82 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 83 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 84 5.1. METRIC Type . . . . . . . . . . . . . . . . . . . . . . . 8 85 6. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 8 86 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 87 7.1. Normative References . . . . . . . . . . . . . . . . . . 8 88 7.2. Informative References . . . . . . . . . . . . . . . . . 9 89 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 91 1. Introduction 93 [RFC5440] describes the Path Computation Element (PCE) Communication 94 Protocol (PCEP). PCEP enables the communication between a Path 95 Computation Client (PCC) and a PCE, or between PCE and PCE, for the 96 purpose of computation of Multiprotocol Label Switching (MPLS) as 97 well as Generalzied MPLS (GMPLS) Traffic Engineering Label Switched 98 Path (TE LSP) characteristics. 100 [RFC8231] specifies a set of extensions to PCEP to enable stateful 101 control of TE LSPs within and across PCEP sessions in compliance with 102 [RFC4657]. It includes mechanisms to effect LSP State 103 Synchronization between PCCs and PCEs, delegation of control over 104 LSPs to PCEs, and PCE control of timing and sequence of path 105 computations within and across PCEP sessions. The model of operation 106 where LSPs are initiated from the PCE is described in [RFC8281]. 108 As per [RFC8402], with Segment Routing (SR), a node steers a packet 109 through an ordered list of instructions, called segments. A segment 110 can represent any instruction, topological or service-based. A 111 segment can have a semantic local to an SR node or global within an 112 SR domain. SR allows to enforce a flow through any path and service 113 chain while maintaining per-flow state only at the ingress node of 114 the SR domain. Segments can be derived from different components: 115 IGP, BGP, Services, Contexts, Locators, etc. The SR architecture can 116 be applied to the MPLS forwarding plane without any change, in which 117 case an SR path corresponds to an MPLS Label Switching Path (LSP). 118 The SR is applied to IPV6 forwarding plane using SRH. A SR path can 119 be derived from an IGP Shortest Path Tree (SPT), but SR-TE paths may 120 not follow IGP SPT. Such paths may be chosen by a suitable network 121 planning tool, or a PCE and provisioned on the ingress node. 123 As per [RFC8664], it is possible to use a stateful PCE for computing 124 one or more SR-TE paths taking into account various constraints and 125 objective functions. Once a path is chosen, the stateful PCE can 126 initiate an SR-TE path on a PCC using PCEP extensions specified in 127 [RFC8281] using the SR specific PCEP extensions specified in 128 [RFC8664]. [RFC8664] specifies PCEP extensions for supporting a SR- 129 TE LSP for MPLS data plane. [I-D.ietf-pce-segment-routing-ipv6] 130 extend PCEP to support SR for IPv6 data plane. 132 The maximum transmission unit (MTU) is the largest size packet or 133 frame, in bytes, that can be sent in a network. An MTU that is too 134 large might cause retransmissions. Too small an MTU might cause the 135 router to send and handle relatively more header overhead and 136 acknowledgments. When an LSP is created across a set of links with 137 different MTU sizes, the ingress router need to know what the 138 smallest MTU is on the LSP path. If this MTU is larger than the MTU 139 of one of the intermediate links, traffic might be dropped, because 140 MPLS packets cannot be fragmented. Also, the ingress router may not 141 be aware of this type of traffic loss, because the control plane for 142 the LSP would still function normally. [RFC3209] specify the 143 mechanism of MTU signaling in RSVP. 145 Since the SR does not require signaling, the path MTU information for 146 SR path is not available. This document specify the extension to 147 PCEP to carry path MTU in the PCEP messages. It is assumed that the 148 PCE is aware of the link MTU as part of the Traffic Engineering 149 Database (TED) population. This could be done via IGP, BGP-LS or 150 some other means. Thus the PCE can find the path MTU at the time of 151 path computation and include this information as part of the PCEP 152 messages. 154 Though the key use case for path MTU is SR, the PCEP extension (as 155 specified in this document) creates a new metric type for path MTU, 156 making this a generic extension that can be used independent of SR. 158 2. Terminology 160 This draft refers to the terms defined in [RFC8201], [RFC4821] and 161 [RFC3988]. 163 MTU: Maximum Transmission Unit, the size in bytes of the largest IP 164 packet, including the IP header and payload, that can be 165 transmitted on a link or path. Note that this could more properly 166 be called the IP MTU, to be consistent with how other standards 167 organizations use the acronym MTU. 169 Link MTU: The Maximum Transmission Unit, i.e., maximum IP packet 170 size in bytes, that can be conveyed in one piece over a link. Be 171 aware that this definition is different from the definition used 172 by other standards organizations. 174 For IETF documents, link MTU is uniformly defined as the IP MTU 175 over the link. This includes the IP header, but excludes link 176 layer headers and other framing that is not part of IP or the IP 177 payload. 179 Be aware that other standards organizations generally define link 180 MTU to include the link layer headers. 182 For the MPLS data plane, this size includes the IP header and data (or 183 other payload) and the label stack but does not include any lower-layer 184 headers. A link may be an interface (such as Ethernet or Packet-over- 185 SONET), a tunnel (such as GRE or IPsec), or an LSP. 187 Path: The set of links traversed by a packet between a source node 188 and a destination node. 190 Path MTU, or PMTU: The minimum link MTU of all the links in a path 191 between a source node and a destination node. 193 For the MPLS data plane, it is the MTU of an LSP from a given LSR to 194 the egress(es), over each valid (forwarding) path. This size includes 195 the IP header and data (or other payload) and any part of the label 196 stack that was received by the ingress LSR before it placed the packet 197 into the LSP (this part of the label stack is considered part of the 198 payload for this LSP). The size does not include any lower-level 199 headers. 201 3. PCEP Extention 203 3.1. Extensions to METRIC Object 205 The METRIC object is defined in Section 7.8 of [RFC5440], comprising 206 metric-value and metric-type (T field), and a flags field, comprising 207 a number of bit flags (B bit and C bit). This document defines a new 208 type for the METRIC object for Path MTU. 210 o T = TBD: Path MTU. 212 o A network comprises of a set of N links {Li, (i=1...N)}. 214 o A path P of a LSP is a list of K links {Lpi,(i=1...K)}. 216 o A Link MTU of link L is denoted M(L). 218 o A Path MTU metric for the path P = Min {M(Lpi), (i=1...K)}. 220 The Path MTU metric type of the METRIC object in PCEP represents the 221 minimum of the Link MTU of all links along the path. 223 When PCE computes the path, it can also find the Path MTU (based on 224 the above criteria) and include this information in the METRIC object 225 with the above metric type in the PCEP message when replying to the 226 PCC. In a Path Computation Reply (PCRep) message, the PCE MAY insert 227 the METRIC object with an Explicit Route Object (ERO) so as to 228 provide the METRIC (path MTU) for the computed path. The PCE MAY 229 also insert the METRIC object with a NO-PATH object to indicate that 230 the metric constraint could not be satisfied. 232 Further, a PCC MAY use the Path MTU metric in a Path Computation 233 Request (PCReq) message to request a path meeting the MTU requirement 234 of the path. In this case, the B bit MUST be set to suggest a bound 235 (a maximum) for the Path MTU metric that must not be exceeded for the 236 PCC to consider the computed path as acceptable. The Path MTU metric 237 must be less than or equal to the value specified in the metric-value 238 field. 240 A PCC can also use this metric to ask PCE to optimize the path MTU 241 during path computation. In this case, the B bit MUST be cleared. 243 The error handling and processing of the METRIC object is as 244 specified in [RFC5440]. 246 3.2. Stateful PCE and PCE Initiated LSPs 248 [RFC8231] specifies a set of extensions to PCEP to enable stateful 249 control of MPLS-TE and GMPLS LSPs via PCEP and the maintaining of 250 these LSPs at the stateful PCE. It further distinguishes between an 251 active and a passive stateful PCE. A passive stateful PCE uses LSP 252 state information learned from PCCs to optimize path computations but 253 does not actively update LSP state. In contrast, an active stateful 254 PCE utilizes the LSP delegation mechanism to update LSP parameters in 255 those PCCs that delegated control over their LSPs to the PCE. 256 [RFC8281] describes the setup, maintenance, and teardown of PCE- 257 initiated LSPs under the stateful PCE model. The document defines 258 the PCInitiate message that is used by a PCE to request a PCC to set 259 up a new LSP. 261 The new metric type defined in this document can also be used with 262 the stateful PCE extensions. The format of PCEP messages described 263 in [RFC8231] and [RFC8281] uses and 264 , respectively, (where the 265 is the attribute-list defined in Section 6.5 of [RFC5440]. 267 A PCE MAY include the path MTU metric in PCInitiate or PCUpd message 268 to inform the PCC of the path MTU calculated for the path. A PCC MAY 269 include the path MTU metric as a bound constraint or to indicate 270 optimization criteria (similar to PCReq). 272 3.3. Segment Routing 274 A Segment Routed path (SR path) can be derived from an IGP Shortest 275 Path Tree (SPT). Segment Routed Traffic Engineering paths (SR-TE 276 paths) may not follow IGP SPT. Such paths may be chosen by a 277 suitable network planning tool and provisioned on the source node of 278 the SR-TE path. 280 It is possible to use a PCE for computing one or more SR-TE paths 281 taking into account various constraints and objective functions. 282 Once a path is chosen, the PCE can inform an SR-TE path on a PCC 283 using PCEP extensions specified in [RFC8664]. Further, 284 [I-D.ietf-pce-segment-routing-ipv6] adds the support for IPv6 data 285 plane in SR. 287 The new metric type for path MTU is applicable for the SR-TE path and 288 require no additional extensions. 290 3.4. Path MTU Adjustment 292 The path MTU metric can be used for both primary and protection path. 294 The minimal value of the link MTU along the path is collected, based 295 on which minor adjustment is made to cater for overhead introduced by 296 the protection mechanisms such as TI-LFA. The path MTU is the value 297 of the minimum link MTU minus the overhead. In this way, the ingress 298 node can use the path MTU directly. 300 4. Security Considerations 302 This document defines a new METRIC type that do not add any new 303 security concerns beyond those discussed in [RFC5440] in itself. 304 Some deployments may find the path MTU information to be extra 305 sensitive and could be used to influence path computation and setup 306 with adverse effect. Additionally, snooping of PCEP messages with 307 such data or using PCEP messages for network reconnaissance may give 308 an attacker sensitive information about the operations of the 309 network. Thus, such deployment should employ suitable PCEP security 310 mechanisms like TCP Authentication Option (TCP-AO) [RFC5925] or 311 Transport Layer Security (TLS) [RFC8253]. The procedure based on TLS 312 is considered a security enhancement and thus is much better suited 313 for the sensitive information. 315 5. IANA Considerations 317 This document makes following requests to IANA for action. 319 5.1. METRIC Type 321 IANA maintains the "Path Computation Element Protocol (PCEP) Numbers" 322 registry. Within this registry, IANA maintains a subregistry for 323 "METRIC Object T Field". IANA is requested to make the following 324 allocation: 326 Value Description Reference 327 ---------------------- ---------------------------- -------------- 328 TBD Path MTU This document 330 6. Acknowledgement 332 We would like to thank Dhruv Dhody for his contributions for this 333 document. 335 7. References 337 7.1. Normative References 339 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 340 Requirement Levels", BCP 14, RFC 2119, 341 DOI 10.17487/RFC2119, March 1997, 342 . 344 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 345 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 346 DOI 10.17487/RFC5440, March 2009, 347 . 349 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 350 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 351 May 2017, . 353 [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path 354 Computation Element Communication Protocol (PCEP) 355 Extensions for Stateful PCE", RFC 8231, 356 DOI 10.17487/RFC8231, September 2017, 357 . 359 [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path 360 Computation Element Communication Protocol (PCEP) 361 Extensions for PCE-Initiated LSP Setup in a Stateful PCE 362 Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, 363 . 365 7.2. Informative References 367 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 368 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 369 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 370 . 372 [RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation 373 Element (PCE) Communication Protocol Generic 374 Requirements", RFC 4657, DOI 10.17487/RFC4657, September 375 2006, . 377 [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP 378 Authentication Option", RFC 5925, DOI 10.17487/RFC5925, 379 June 2010, . 381 [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody, 382 "PCEPS: Usage of TLS to Provide a Secure Transport for the 383 Path Computation Element Communication Protocol (PCEP)", 384 RFC 8253, DOI 10.17487/RFC8253, October 2017, 385 . 387 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 388 Decraene, B., Litkowski, S., and R. Shakir, "Segment 389 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 390 July 2018, . 392 [RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 393 and J. Hardwick, "Path Computation Element Communication 394 Protocol (PCEP) Extensions for Segment Routing", RFC 8664, 395 DOI 10.17487/RFC8664, December 2019, 396 . 398 [I-D.ietf-pce-segment-routing-ipv6] 399 Li, C., Negi, M., Koldychev, M., Kaladharan, P., and Y. 400 Zhu, "PCEP Extensions for Segment Routing leveraging the 401 IPv6 data plane", draft-ietf-pce-segment-routing-ipv6-06 402 (work in progress), July 2020. 404 Authors' Addresses 406 Shuping Peng 407 Huawei Technologies 408 Huawei Campus, No. 156 Beiqing Rd. 409 Beijing 100095 410 China 412 Email: pengshuping@huawei.com 414 Cheng Li 415 Huawei Technologies 416 Huawei Campus, No. 156 Beiqing Rd. 417 Beijing 100095 418 China 420 Email: c.l@huawei.com 422 Liuyan Han 423 China Mobile 424 Beijing 100053 425 China 427 Email: hanliuyan@chinamobile.com 429 Luc-Fabrice Ndifor 430 MTN Cameroon 431 Cameroon 433 Email: Luc-Fabrice.Ndifor@mtn.com