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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-25) exists of draft-ietf-pce-segment-routing-ipv6-06 Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--).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: January 6, 2021 L. Han 6 China Mobile 7 July 5, 2020 9 Support for Path MTU (PMTU) in the Path Computation Element (PCE) 10 communication Protocol (PCEP). 11 draft-li-pce-pcep-pmtu-01 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 January 6, 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. PCEP Extention . . . . . . . . . . . . . . . . . . . . . . . 4 75 2.1. Extensions to METRIC Object . . . . . . . . . . . . . . . 4 76 2.2. Stateful PCE and PCE Initiated LSPs . . . . . . . . . . . 5 77 2.3. Segement Routing . . . . . . . . . . . . . . . . . . . . 5 78 3. Security Considerations . . . . . . . . . . . . . . . . . . . 6 79 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 80 4.1. METRIC Types . . . . . . . . . . . . . . . . . . . . . . 6 81 5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 82 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 83 6.1. Normative References . . . . . . . . . . . . . . . . . . 6 84 6.2. Informative References . . . . . . . . . . . . . . . . . 7 85 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 87 1. Introduction 89 [RFC5440] describes the Path Computation Element (PCE) Communication 90 Protocol (PCEP). PCEP enables the communication between a Path 91 Computation Client (PCC) and a PCE, or between PCE and PCE, for the 92 purpose of computation of Multiprotocol Label Switching (MPLS) as 93 well as Generalzied MPLS (GMPLS) Traffic Engineering Label Switched 94 Path (TE LSP) characteristics. 96 [RFC8231] specifies a set of extensions to PCEP to enable stateful 97 control of TE LSPs within and across PCEP sessions in compliance with 98 [RFC4657]. It includes mechanisms to effect LSP State 99 Synchronization between PCCs and PCEs, delegation of control over 100 LSPs to PCEs, and PCE control of timing and sequence of path 101 computations within and across PCEP sessions. The model of operation 102 where LSPs are initiated from the PCE is described in [RFC8281]. 104 As per [RFC8402], with Segment Routing (SR), a node steers a packet 105 through an ordered list of instructions, called segments. A segment 106 can represent any instruction, topological or service-based. A 107 segment can have a semantic local to an SR node or global within an 108 SR domain. SR allows to enforce a flow through any path and service 109 chain while maintaining per-flow state only at the ingress node of 110 the SR domain. Segments can be derived from different components: 111 IGP, BGP, Services, Contexts, Locators, etc. The SR architecture can 112 be applied to the MPLS forwarding plane without any change, in which 113 case an SR path corresponds to an MPLS Label Switching Path (LSP). 114 The SR is applied to IPV6 forwarding plane using SRH. A SR path can 115 be derived from an IGP Shortest Path Tree (SPT), but SR-TE paths may 116 not follow IGP SPT. Such paths may be chosen by a suitable network 117 planning tool, or a PCE and provisioned on the ingress node. 119 As per [RFC8664], it is possible to use a stateful PCE for computing 120 one or more SR-TE paths taking into account various constraints and 121 objective functions. Once a path is chosen, the stateful PCE can 122 initiate an SR-TE path on a PCC using PCEP extensions specified in 123 [RFC8281] using the SR specific PCEP extensions specified in 124 [RFC8664]. [RFC8664] specifies PCEP extensions for supporting a SR- 125 TE LSP for MPLS data plane. [I-D.ietf-pce-segment-routing-ipv6] 126 extend PCEP to support SR for IPv6 data plane. 128 The maximum transmission unit (MTU) is the largest size packet or 129 frame, in bytes, that can be sent in a network. An MTU that is too 130 large might cause retransmissions. Too small an MTU might cause the 131 router to send and handle relatively more header overhead and 132 acknowledgments. When an LSP is created across a set of links with 133 different MTU sizes, the ingress router need to know what the 134 smallest MTU is on the LSP path. If this MTU is larger than the MTU 135 of one of the intermediate links, traffic might be dropped, because 136 MPLS packets cannot be fragmented. Also, the ingress router may not 137 be aware of this type of traffic loss, because the control plane for 138 the LSP would still function normally. [RFC3209] specify the 139 mechanism of MTU signaling in RSVP. 141 Since the SR does not require signaling, the path MTU information for 142 SR path is not available. This document specify the extension to 143 PCEP to carry path MTU in the PCEP messages. It is assumed that the 144 PCE is aware of the link MTU as part of the Traffic Engineering 145 Database (TED) population. This could be done via IGP, BGP-LS or 146 some other means. Thus the PCE can find the path MTU at the time of 147 path computation and include this information as part of the PCEP 148 messages. 150 Though the key use case for path MTU is SR, the PCEP extension (as 151 specified in this document) creates a new metric type for path MTU, 152 making this a generic extension that can be used independent of SR. 154 2. PCEP Extention 156 2.1. Extensions to METRIC Object 158 The METRIC object is defined in Section 7.8 of [RFC5440], comprising 159 metric-value and metric-type (T field), and a flags field, comprising 160 a number of bit flags (B bit and C bit). This document defines a new 161 type for the METRIC object for Path MTU. 163 o T = TBD: Path MTU. 165 o A network comprises of a set of N links {Li, (i=1...N)}. 167 o A path P of a LSP is a list of K links {Lpi,(i=1...K)}. 169 o A Link MTU of link L is denoted M(L). 171 o A Path MTU metric for the path P = Min {M(Lpi), (i=1...K)}. 173 The Path MTU metric type of the METRIC object in PCEP represents the 174 minimum of the Link MTU of all links along the path. 176 When PCE computes the path, it can also find the Path MTU (based on 177 the above criteria) and include this information in the METRIC object 178 with the above metric type in the PCEP message when replying to the 179 PCC. In a Path Computation Reply (PCRep) message, the PCE MAY insert 180 the METRIC object with an Explicit Route Object (ERO) so as to 181 provide the METRIC (path MTU) for the computed path. The PCE MAY 182 also insert the METRIC object with a NO-PATH object to indicate that 183 the metric constraint could not be satisfied. 185 Further, a PCC MAY use the Path MTU metric in a Path Computation 186 Request (PCReq) message to request a path meeting the MTU requirement 187 of the path. In this case, the B bit MUST be set to suggest a bound 188 (a maximum) for the Path MTU metric that must not be exceeded for the 189 PCC to consider the computed path as acceptable. The Path MTU metric 190 must be less than or equal to the value specified in the metric-value 191 field. 193 A PCC can also use this metric to ask PCE to optimize the path MTU 194 during path computation. In this case, the B bit MUST be cleared. 196 The error handling and processing of the METRIC object is as 197 specified in [RFC5440]. 199 2.2. Stateful PCE and PCE Initiated LSPs 201 [RFC8231] specifies a set of extensions to PCEP to enable stateful 202 control of MPLS-TE and GMPLS LSPs via PCEP and the maintaining of 203 these LSPs at the stateful PCE. It further distinguishes between an 204 active and a passive stateful PCE. A passive stateful PCE uses LSP 205 state information learned from PCCs to optimize path computations but 206 does not actively update LSP state. In contrast, an active stateful 207 PCE utilizes the LSP delegation mechanism to update LSP parameters in 208 those PCCs that delegated control over their LSPs to the PCE. 209 [RFC8281] describes the setup, maintenance, and teardown of PCE- 210 initiated LSPs under the stateful PCE model. The document defines 211 the PCInitiate message that is used by a PCE to request a PCC to set 212 up a new LSP. 214 The new metric type defined in this document can also be used with 215 the stateful PCE extensions. The format of PCEP messages described 216 in [RFC8231] and [RFC8281] uses and 217 , respectively, (where the 218 is the attribute-list defined in Section 6.5 of [RFC5440]. 220 A PCE MAY include the path MTU metric in PCInitiate or PCUpd message 221 to inform the PCC of the path MTU calculated for the path. A PCC MAY 222 include the path MTU metric as a bound constraint or to indicate 223 optimization criteria (similar to PCReq). 225 2.3. Segement Routing 227 A Segment Routed path (SR path) can be derived from an IGP Shortest 228 Path Tree (SPT). Segment Routed Traffic Engineering paths (SR-TE 229 paths) may not follow IGP SPT. Such paths may be chosen by a 230 suitable network planning tool and provisioned on the source node of 231 the SR-TE path. 233 It is possible to use a PCE for computing one or more SR-TE paths 234 taking into account various constraints and objective functions. 235 Once a path is chosen, the PCE can inform an SR-TE path on a PCC 236 using PCEP extensions specified in [RFC8664]. Further, 237 [I-D.ietf-pce-segment-routing-ipv6] adds the support for IPv6 data 238 plane in SR. 240 The new metric type for path MTU is applicable for the SR-TE path and 241 require no additional extensions. 243 3. Security Considerations 245 This document defines a new METRIC type that do not add any new 246 security concerns beyond those discussed in [RFC5440] in itself. 247 Some deployments may find the path MTU information to be extra 248 sensitive and could be used to influence path computation and setup 249 with adverse effect. Additionally, snooping of PCEP messages with 250 such data or using PCEP messages for network reconnaissance may give 251 an attacker sensitive information about the operations of the 252 network. Thus, such deployment should employ suitable PCEP security 253 mechanisms like TCP Authentication Option (TCP-AO) [RFC5925] or 254 Transport Layer Security (TLS) [RFC8253]. The procedure based on TLS 255 is considered a security enhancement and thus is much better suited 256 for the sensitive information. 258 4. IANA Considerations 260 This document makes following requests to IANA for action. 262 4.1. METRIC Types 264 IANA maintains the "Path Computation Element Protocol (PCEP) Numbers" 265 registry. Within this registry, IANA maintains a subregistry for 266 "METRIC Object T Field". IANA is requested to make the following 267 allocation: 269 Value Description Reference 270 ---------------------- ---------------------------- -------------- 271 TBD Path MTU. This document 273 5. Acknowledgments 275 We would like to thank Dhruv Dhody for his contributions for this 276 document. 278 6. References 280 6.1. Normative References 282 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 283 Requirement Levels", BCP 14, RFC 2119, 284 DOI 10.17487/RFC2119, March 1997, 285 . 287 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 288 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 289 DOI 10.17487/RFC5440, March 2009, 290 . 292 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 293 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 294 May 2017, . 296 [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path 297 Computation Element Communication Protocol (PCEP) 298 Extensions for Stateful PCE", RFC 8231, 299 DOI 10.17487/RFC8231, September 2017, 300 . 302 [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path 303 Computation Element Communication Protocol (PCEP) 304 Extensions for PCE-Initiated LSP Setup in a Stateful PCE 305 Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, 306 . 308 6.2. Informative References 310 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 311 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 312 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 313 . 315 [RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation 316 Element (PCE) Communication Protocol Generic 317 Requirements", RFC 4657, DOI 10.17487/RFC4657, September 318 2006, . 320 [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP 321 Authentication Option", RFC 5925, DOI 10.17487/RFC5925, 322 June 2010, . 324 [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody, 325 "PCEPS: Usage of TLS to Provide a Secure Transport for the 326 Path Computation Element Communication Protocol (PCEP)", 327 RFC 8253, DOI 10.17487/RFC8253, October 2017, 328 . 330 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 331 Decraene, B., Litkowski, S., and R. Shakir, "Segment 332 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 333 July 2018, . 335 [RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., 336 and J. Hardwick, "Path Computation Element Communication 337 Protocol (PCEP) Extensions for Segment Routing", RFC 8664, 338 DOI 10.17487/RFC8664, December 2019, 339 . 341 [I-D.ietf-pce-segment-routing-ipv6] 342 Li, C., Negi, M., Koldychev, M., Kaladharan, P., and Y. 343 Zhu, "PCEP Extensions for Segment Routing leveraging the 344 IPv6 data plane", draft-ietf-pce-segment-routing-ipv6-06 345 (work in progress), July 2020. 347 Authors' Addresses 349 Shuping Peng 350 Huawei Technologies 351 Huawei Campus, No. 156 Beiqing Rd. 352 Beijing 100095 353 China 355 Email: pengshuping@huawei.com 357 Cheng Li 358 Huawei Technologies 359 Huawei Campus, No. 156 Beiqing Rd. 360 Beijing 100095 361 China 363 Email: c.l@huawei.com 365 Liuyan Han 366 China Mobile 367 Beijing 100053 368 China 370 Email: hanliuyan@chinamobile.com