idnits 2.17.1 draft-li-pce-pcep-pmtu-02.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 : ---------------------------------------------------------------------------- ** There are 8 instances of too long lines in the document, the longest one being 5 characters in excess of 72. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (August 23, 2020) is 1314 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) == Missing Reference: 'RFC8201' is mentioned on line 158, but not defined == Missing Reference: 'RFC4821' is mentioned on line 158, but not defined == Missing Reference: 'RFC3988' is mentioned on line 159, but not defined == Outdated reference: A later version (-22) exists of draft-ietf-pce-segment-routing-ipv6-06 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--).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: February 24, 2021 L. Han 6 China Mobile 7 August 23, 2020 9 Support for Path MTU (PMTU) in the Path Computation Element (PCE) 10 communication Protocol (PCEP). 11 draft-li-pce-pcep-pmtu-02 13 Abstract 15 The Path Computation Element (PCE) provides path computation 16 functions in support of traffic engineering in Multiprotocol Label 17 Switching (MPLS) and Generalized MPLS (GMPLS) networks. 19 The Source Packet Routing in Networking (SPRING) architecture 20 describes how Segment Routing (SR) can be used to steer packets 21 through an IPv6 or MPLS network using the source routing paradigm. A 22 Segment Routed Path can be derived from a variety of mechanisms, 23 including an IGP Shortest Path Tree (SPT), explicit configuration, or 24 a Path Computation Element (PCE). 26 Since the SR does not require signaling, the path maximum 27 transmission unit (MTU) information for SR path is not available. 28 This document specify the extension to PCE communication protocol 29 (PCEP) to carry path (MTU) in the PCEP messages. 31 Requirements Language 33 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 34 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 35 "OPTIONAL" in this document are to be interpreted as described in BCP 36 14 [RFC2119] [RFC8174] when, and only when, they appear in all 37 capitals, as shown here. 39 Status of This Memo 41 This Internet-Draft is submitted in full conformance with the 42 provisions of BCP 78 and BCP 79. 44 Internet-Drafts are working documents of the Internet Engineering 45 Task Force (IETF). Note that other groups may also distribute 46 working documents as Internet-Drafts. The list of current Internet- 47 Drafts is at https://datatracker.ietf.org/drafts/current/. 49 Internet-Drafts are draft documents valid for a maximum of six months 50 and may be updated, replaced, or obsoleted by other documents at any 51 time. It is inappropriate to use Internet-Drafts as reference 52 material or to cite them other than as "work in progress." 54 This Internet-Draft will expire on February 24, 2021. 56 Copyright Notice 58 Copyright (c) 2020 IETF Trust and the persons identified as the 59 document authors. All rights reserved. 61 This document is subject to BCP 78 and the IETF Trust's Legal 62 Provisions Relating to IETF Documents 63 (https://trustee.ietf.org/license-info) in effect on the date of 64 publication of this document. Please review these documents 65 carefully, as they describe your rights and restrictions with respect 66 to this document. Code Components extracted from this document must 67 include Simplified BSD License text as described in Section 4.e of 68 the Trust Legal Provisions and are provided without warranty as 69 described in the Simplified BSD License. 71 Table of Contents 73 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 74 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 75 3. PCEP Extention . . . . . . . . . . . . . . . . . . . . . . . 5 76 3.1. Extensions to METRIC Object . . . . . . . . . . . . . . . 5 77 3.2. Stateful PCE and PCE Initiated LSPs . . . . . . . . . . . 6 78 3.3. Segment Routing . . . . . . . . . . . . . . . . . . . . . 7 79 3.4. Path MTU Adjustment . . . . . . . . . . . . . . . . . . . 7 80 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7 81 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 82 5.1. METRIC Type . . . . . . . . . . . . . . . . . . . . . . . 8 83 6. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 8 84 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 85 7.1. Normative References . . . . . . . . . . . . . . . . . . 8 86 7.2. Informative References . . . . . . . . . . . . . . . . . 9 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 89 1. Introduction 91 [RFC5440] describes the Path Computation Element (PCE) Communication 92 Protocol (PCEP). PCEP enables the communication between a Path 93 Computation Client (PCC) and a PCE, or between PCE and PCE, for the 94 purpose of computation of Multiprotocol Label Switching (MPLS) as 95 well as Generalzied MPLS (GMPLS) Traffic Engineering Label Switched 96 Path (TE LSP) characteristics. 98 [RFC8231] specifies a set of extensions to PCEP to enable stateful 99 control of TE LSPs within and across PCEP sessions in compliance with 100 [RFC4657]. It includes mechanisms to effect LSP State 101 Synchronization between PCCs and PCEs, delegation of control over 102 LSPs to PCEs, and PCE control of timing and sequence of path 103 computations within and across PCEP sessions. The model of operation 104 where LSPs are initiated from the PCE is described in [RFC8281]. 106 As per [RFC8402], with Segment Routing (SR), a node steers a packet 107 through an ordered list of instructions, called segments. A segment 108 can represent any instruction, topological or service-based. A 109 segment can have a semantic local to an SR node or global within an 110 SR domain. SR allows to enforce a flow through any path and service 111 chain while maintaining per-flow state only at the ingress node of 112 the SR domain. Segments can be derived from different components: 113 IGP, BGP, Services, Contexts, Locators, etc. The SR architecture can 114 be applied to the MPLS forwarding plane without any change, in which 115 case an SR path corresponds to an MPLS Label Switching Path (LSP). 116 The SR is applied to IPV6 forwarding plane using SRH. A SR path can 117 be derived from an IGP Shortest Path Tree (SPT), but SR-TE paths may 118 not follow IGP SPT. Such paths may be chosen by a suitable network 119 planning tool, or a PCE and provisioned on the ingress node. 121 As per [RFC8664], it is possible to use a stateful PCE for computing 122 one or more SR-TE paths taking into account various constraints and 123 objective functions. Once a path is chosen, the stateful PCE can 124 initiate an SR-TE path on a PCC using PCEP extensions specified in 125 [RFC8281] using the SR specific PCEP extensions specified in 126 [RFC8664]. [RFC8664] specifies PCEP extensions for supporting a SR- 127 TE LSP for MPLS data plane. [I-D.ietf-pce-segment-routing-ipv6] 128 extend PCEP to support SR for IPv6 data plane. 130 The maximum transmission unit (MTU) is the largest size packet or 131 frame, in bytes, that can be sent in a network. An MTU that is too 132 large might cause retransmissions. Too small an MTU might cause the 133 router to send and handle relatively more header overhead and 134 acknowledgments. When an LSP is created across a set of links with 135 different MTU sizes, the ingress router need to know what the 136 smallest MTU is on the LSP path. If this MTU is larger than the MTU 137 of one of the intermediate links, traffic might be dropped, because 138 MPLS packets cannot be fragmented. Also, the ingress router may not 139 be aware of this type of traffic loss, because the control plane for 140 the LSP would still function normally. [RFC3209] specify the 141 mechanism of MTU signaling in RSVP. 143 Since the SR does not require signaling, the path MTU information for 144 SR path is not available. This document specify the extension to 145 PCEP to carry path MTU in the PCEP messages. It is assumed that the 146 PCE is aware of the link MTU as part of the Traffic Engineering 147 Database (TED) population. This could be done via IGP, BGP-LS or 148 some other means. Thus the PCE can find the path MTU at the time of 149 path computation and include this information as part of the PCEP 150 messages. 152 Though the key use case for path MTU is SR, the PCEP extension (as 153 specified in this document) creates a new metric type for path MTU, 154 making this a generic extension that can be used independent of SR. 156 2. Terminology 158 This draft refers to the terms defined in [RFC8201], [RFC4821] and 159 [RFC3988]. 161 MTU: Maximum Transmission Unit, the size in bytes of the largest IP 162 packet, including the IP header and payload, that can be 163 transmitted on a link or path. Note that this could more properly 164 be called the IP MTU, to be consistent with how other standards 165 organizations use the acronym MTU. 167 Link MTU: The Maximum Transmission Unit, i.e., maximum IP packet 168 size in bytes, that can be conveyed in one piece over a link. Be 169 aware that this definition is different from the definition used 170 by other standards organizations. 172 For IETF documents, link MTU is uniformly defined as the IP MTU 173 over the link. This includes the IP header, but excludes link 174 layer headers and other framing that is not part of IP or the IP 175 payload. 177 Be aware that other standards organizations generally define link 178 MTU to include the link layer headers. 180 For the MPLS data plane, this size includes the IP header and data (or 181 other payload) and the label stack but does not include any lower-layer 182 headers. A link may be an interface (such as Ethernet or Packet-over- 183 SONET), a tunnel (such as GRE or IPsec), or an LSP. 185 Path: The set of links traversed by a packet between a source node 186 and a destination node. 188 Path MTU, or PMTU: The minimum link MTU of all the links in a path 189 between a source node and a destination node. 191 For the MPLS data plane, it is the MTU of an LSP from a given LSR to 192 the egress(es), over each valid (forwarding) path. This size includes 193 the IP header and data (or other payload) and any part of the label 194 stack that was received by the ingress LSR before it placed the packet 195 into the LSP (this part of the label stack is considered part of the 196 payload for this LSP). The size does not include any lower-level 197 headers. 199 3. PCEP Extention 201 3.1. Extensions to METRIC Object 203 The METRIC object is defined in Section 7.8 of [RFC5440], comprising 204 metric-value and metric-type (T field), and a flags field, comprising 205 a number of bit flags (B bit and C bit). This document defines a new 206 type for the METRIC object for Path MTU. 208 o T = TBD: Path MTU. 210 o A network comprises of a set of N links {Li, (i=1...N)}. 212 o A path P of a LSP is a list of K links {Lpi,(i=1...K)}. 214 o A Link MTU of link L is denoted M(L). 216 o A Path MTU metric for the path P = Min {M(Lpi), (i=1...K)}. 218 The Path MTU metric type of the METRIC object in PCEP represents the 219 minimum of the Link MTU of all links along the path. 221 When PCE computes the path, it can also find the Path MTU (based on 222 the above criteria) and include this information in the METRIC object 223 with the above metric type in the PCEP message when replying to the 224 PCC. In a Path Computation Reply (PCRep) message, the PCE MAY insert 225 the METRIC object with an Explicit Route Object (ERO) so as to 226 provide the METRIC (path MTU) for the computed path. The PCE MAY 227 also insert the METRIC object with a NO-PATH object to indicate that 228 the metric constraint could not be satisfied. 230 Further, a PCC MAY use the Path MTU metric in a Path Computation 231 Request (PCReq) message to request a path meeting the MTU requirement 232 of the path. In this case, the B bit MUST be set to suggest a bound 233 (a maximum) for the Path MTU metric that must not be exceeded for the 234 PCC to consider the computed path as acceptable. The Path MTU metric 235 must be less than or equal to the value specified in the metric-value 236 field. 238 A PCC can also use this metric to ask PCE to optimize the path MTU 239 during path computation. In this case, the B bit MUST be cleared. 241 The error handling and processing of the METRIC object is as 242 specified in [RFC5440]. 244 3.2. Stateful PCE and PCE Initiated LSPs 246 [RFC8231] specifies a set of extensions to PCEP to enable stateful 247 control of MPLS-TE and GMPLS LSPs via PCEP and the maintaining of 248 these LSPs at the stateful PCE. It further distinguishes between an 249 active and a passive stateful PCE. A passive stateful PCE uses LSP 250 state information learned from PCCs to optimize path computations but 251 does not actively update LSP state. In contrast, an active stateful 252 PCE utilizes the LSP delegation mechanism to update LSP parameters in 253 those PCCs that delegated control over their LSPs to the PCE. 254 [RFC8281] describes the setup, maintenance, and teardown of PCE- 255 initiated LSPs under the stateful PCE model. The document defines 256 the PCInitiate message that is used by a PCE to request a PCC to set 257 up a new LSP. 259 The new metric type defined in this document can also be used with 260 the stateful PCE extensions. The format of PCEP messages described 261 in [RFC8231] and [RFC8281] uses and 262 , respectively, (where the 263 is the attribute-list defined in Section 6.5 of [RFC5440]. 265 A PCE MAY include the path MTU metric in PCInitiate or PCUpd message 266 to inform the PCC of the path MTU calculated for the path. A PCC MAY 267 include the path MTU metric as a bound constraint or to indicate 268 optimization criteria (similar to PCReq). 270 3.3. Segment Routing 272 A Segment Routed path (SR path) can be derived from an IGP Shortest 273 Path Tree (SPT). Segment Routed Traffic Engineering paths (SR-TE 274 paths) may not follow IGP SPT. Such paths may be chosen by a 275 suitable network planning tool and provisioned on the source node of 276 the SR-TE path. 278 It is possible to use a PCE for computing one or more SR-TE paths 279 taking into account various constraints and objective functions. 280 Once a path is chosen, the PCE can inform an SR-TE path on a PCC 281 using PCEP extensions specified in [RFC8664]. Further, 282 [I-D.ietf-pce-segment-routing-ipv6] adds the support for IPv6 data 283 plane in SR. 285 The new metric type for path MTU is applicable for the SR-TE path and 286 require no additional extensions. 288 3.4. Path MTU Adjustment 290 The path MTU metric can be used for both primary and protection path. 292 The minimal value of the link MTU along the path is collected, based 293 on which minor adjustment is made to cater for overhead introduced by 294 the protection mechanisms such as TI-LFA. The path MTU is the value 295 of the minimum link MTU minus the overhead. In this way, the ingress 296 node can use the path MTU directly. 298 4. Security Considerations 300 This document defines a new METRIC type that do not add any new 301 security concerns beyond those discussed in [RFC5440] in itself. 302 Some deployments may find the path MTU information to be extra 303 sensitive and could be used to influence path computation and setup 304 with adverse effect. Additionally, snooping of PCEP messages with 305 such data or using PCEP messages for network reconnaissance may give 306 an attacker sensitive information about the operations of the 307 network. Thus, such deployment should employ suitable PCEP security 308 mechanisms like TCP Authentication Option (TCP-AO) [RFC5925] or 309 Transport Layer Security (TLS) [RFC8253]. The procedure based on TLS 310 is considered a security enhancement and thus is much better suited 311 for the sensitive information. 313 5. IANA Considerations 315 This document makes following requests to IANA for action. 317 5.1. METRIC Type 319 IANA maintains the "Path Computation Element Protocol (PCEP) Numbers" 320 registry. Within this registry, IANA maintains a subregistry for 321 "METRIC Object T Field". IANA is requested to make the following 322 allocation: 324 Value Description Reference 325 ---------------------- ---------------------------- -------------- 326 TBD Path MTU This document 328 6. Acknowledgement 330 We would like to thank Dhruv Dhody for his contributions for this 331 document. 333 7. References 335 7.1. Normative References 337 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 338 Requirement Levels", BCP 14, RFC 2119, 339 DOI 10.17487/RFC2119, March 1997, 340 . 342 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 343 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 344 DOI 10.17487/RFC5440, March 2009, 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 [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path 352 Computation Element Communication Protocol (PCEP) 353 Extensions for Stateful PCE", RFC 8231, 354 DOI 10.17487/RFC8231, September 2017, 355 . 357 [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path 358 Computation Element Communication Protocol (PCEP) 359 Extensions for PCE-Initiated LSP Setup in a Stateful PCE 360 Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, 361 . 363 7.2. Informative References 365 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 366 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 367 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 368 . 370 [RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation 371 Element (PCE) Communication Protocol Generic 372 Requirements", RFC 4657, DOI 10.17487/RFC4657, September 373 2006, . 375 [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP 376 Authentication Option", RFC 5925, DOI 10.17487/RFC5925, 377 June 2010, . 379 [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody, 380 "PCEPS: Usage of TLS to Provide a Secure Transport for the 381 Path Computation Element Communication Protocol (PCEP)", 382 RFC 8253, DOI 10.17487/RFC8253, October 2017, 383 . 385 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 386 Decraene, B., Litkowski, S., and R. Shakir, "Segment 387 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 388 July 2018, . 390 [RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 391 and J. Hardwick, "Path Computation Element Communication 392 Protocol (PCEP) Extensions for Segment Routing", RFC 8664, 393 DOI 10.17487/RFC8664, December 2019, 394 . 396 [I-D.ietf-pce-segment-routing-ipv6] 397 Li, C., Negi, M., Koldychev, M., Kaladharan, P., and Y. 398 Zhu, "PCEP Extensions for Segment Routing leveraging the 399 IPv6 data plane", draft-ietf-pce-segment-routing-ipv6-06 400 (work in progress), July 2020. 402 Authors' Addresses 404 Shuping Peng 405 Huawei Technologies 406 Huawei Campus, No. 156 Beiqing Rd. 407 Beijing 100095 408 China 410 Email: pengshuping@huawei.com 412 Cheng Li 413 Huawei Technologies 414 Huawei Campus, No. 156 Beiqing Rd. 415 Beijing 100095 416 China 418 Email: c.l@huawei.com 420 Liuyan Han 421 China Mobile 422 Beijing 100053 423 China 425 Email: hanliuyan@chinamobile.com