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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) ** Downref: Normative reference to an Informational RFC: RFC 4655 ** Obsolete normative reference: RFC 7525 (Obsoleted by RFC 9325) ** Obsolete normative reference: RFC 7752 (Obsoleted by RFC 9552) Summary: 3 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group A. Stone 3 Internet-Draft M. Aissaoui 4 Intended status: Standards Track Nokia 5 Expires: April 27, 2020 October 25, 2019 7 Path Protection Enforcement in PCEP 8 draft-stone-pce-path-protection-enforcement-00 10 Abstract 12 This document aims to clarify existing usage of the local protection 13 desired bit signalled in Path Computation Element Protocol (PCEP). 14 This document also introduces a new flag for signalling protection 15 strictness in PCEP. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on April 27, 2020. 34 Copyright Notice 36 Copyright (c) 2019 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (https://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 53 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. Protection Enforcement Flag (E-Flag) . . . . . . . . . . . . 4 55 3. Security Considerations . . . . . . . . . . . . . . . . . . . 5 56 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 57 4.1. LSP Attributes Protection Enforcement Flag . . . . . . . 6 58 5. Normative References . . . . . . . . . . . . . . . . . . . . 6 59 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 61 1. Introduction 63 Path Computation Element (PCE) Communication Protocol (PCEP) 64 [RFC5440] enables the communication between a Path Computation Client 65 (PCC) and a Path Control Element (PCE), or between two PCEs based on 66 the PCE architecture [RFC4655] . 68 PCEP [RFC5440] utilizes flags, values and concepts previously defined 69 in RSVP-TE Extensions [RFC3209] and Fast Reroute Extensions to RSVP- 70 TE [RFC4090] . One such concept in PCEP is the "Local Protection 71 Desired" (L-flag in the LSPA Object in RFC5440), which was originally 72 defined in the SESSION-ATTRIBUTE Object in RFC3209. In RSVP, this 73 flag signals to downstream routers that local protection is desired, 74 which indicates to transit routers that they may use a local repair 75 mechanism. The headend router calculating the path does not know 76 whether a downstream router will or will not protect a hop during 77 it's calculation. Therefore, a local protection desired does not 78 require the transit router to satisfy protection in order to 79 establish the RSVP signalled path. This flag is signalled in PCEP as 80 an attribute of the LSP via the LSP Attributes object. 82 PCEP Extensions for Segment Routing (draft-ietf-pce-segment-routing) 83 extends support in PCEP for Segment Routed LSPs (SR-LSPs) as defined 84 in the Segment Routing Architecture [RFC8402] . As per the Segment 85 Routing Architecture, Adjacency Segment Identifiers(Adj-SID) may be 86 eligible for protection (using IPFRR or MPLS-FRR). The protection 87 eligibility is advertised into IGP (draft-ietf-ospf-segment-routing- 88 extensions and draft-ietf-isis-segment-routing-extensions) as the 89 B-Flag part of the Adjacency SID sub-tlv and can be discovered by a 90 PCE via BGP-LS [RFC7752] using the BGP-LS Segment Routing Extensions 91 (draft-ietf-idr-bgp-ls-segment-routing-ext). An Adjacency SID may or 92 may not have protection eligibility and for a given adjacency between 93 two routers there may be multiple Adjacency SIDs, some of which are 94 protected and some which are not. 96 A Segment Routed path calculated by PCE may contain various types of 97 segments, as defined in [RFC8402] such as Adjacency, Node or Binding. 98 The protection eligibility for Adjacency SIDs can be discovered by 99 PCE, so therefore the PCE can take the protection eligibility into 100 consideration as a path constraint. If a path is calculated to 101 include other segment identifiers which are not applicable to having 102 their protection state advertised, as they may only be locally 103 significant for each router processing the SID such as Node SIDs, it 104 may not be possible for PCE to include the protection constraint as 105 part of the path calculation. 107 It is desirable for an operator to define the enforcement, or 108 strictness of the protection requirement when it can be applied. 110 As defined in [RFC5440] the mechanism to signal protection 111 enforcement in PCEP is with the previously mentioned L-flag defined 112 in the LSPA Object. The name of the flag uses the term "Desired", 113 which by definition means "strongly wished for or intended" and is 114 rooted in the RSVP use case. For RSVP, this is not within control of 115 the PCE. However, [RFC5440] does state "When set, this means that 116 the computed path must include links protected with Fast Reroute as 117 defined in [RFC4090]." Implementations of [RFC5440] have either 118 interpreted the L-Flag as PROTECTION MANDATORY or PROTECTION 119 PREFERRED, leading to operational differences. The boolean bit flag 120 is unable to distinguish between the the different options of 121 PROTECTION MANDATORY, UNPROTECTED MANDATORY, PROTECTION PREFERRED and 122 UNPROTECTED PREFERRED. 124 1.1. Requirements Language 126 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 127 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 128 document are to be interpreted as described in RFC 2119 [RFC2119]. 130 1.2. Terminology 132 This document uses the following terminology: 134 PROTECTION MANDATORY: path MUST have protection eligibility on all 135 links. 137 UNPROTECTED MANDATORY: path MUST NOT have protection eligibility on 138 all links. 140 PROTECTION PREFERRED: path SHOULD have protection eligibility on all 141 links but MAY contain links which do not have protection eligibility. 143 UNPROTECTED PREFERRED: path SHOULD NOT have protection eligibility on 144 all links but MAY contain links which have protection eligibility. 146 PCC: Path Computation Client. Any client application requesting a 147 path computation to be performed by a Path Computation Element. 149 PCE: Path Computation Element. An entity (component, application, or 150 network node) that is capable of computing a network path or route 151 based on a network graph and applying computational constraints. 153 PCEP: Path Computation Element Protocol. 155 2. Protection Enforcement Flag (E-Flag) 157 Section 7.11 in Path Computation Element Protocol [RFC5440] describes 158 the encoding of the Local Protection Desired (L-Flag). A new flag is 159 proposed in this document in the LSP Attributes Object which extends 160 the L-Flag to identify the protection enforcement. 162 The flag bit is to be allocated by IANA following IETF Consensus. 164 This draft version proposes using bit 6. 166 Codespace of the Flag field (LSPA Object) 168 Bit Description Reference 170 7 Local Protection Desired RFC5440 172 6 Local Protection Enforcement This document 174 The format of the LSPA Object as defined in [RFC5440] is: 176 0 1 2 3 177 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 1 178 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 179 | Exclude-any | 180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 181 | Include-any | 182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 183 | Include-all | 184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 185 | Setup Prio | Holding Prio | Flags |E|L| Reserved | 186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 187 | | 188 // Optional TLVs // 189 | | 190 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 192 Flags (8 bits) 194 o L flag: As defined in [RFC5440] and further updated by this 195 document. When set, protection is desired. When not set, 196 protection is not desired. The enforcement of the protection is 197 identified via the E-Flag. 199 o E flag (Protection Enforcement): When set, the value of the L-Flag 200 MUST be treated as a MUST constraint where applicable, when 201 protection state of a SID is known. When E flag is not set, the 202 value of the L-Flag MUST be treated as a MAY constraint. 204 When L-flag is set and E-flag is set then PCE MUST consider the 205 protection eligibility as PROTECTION MANDATORY constraint. 207 When L-flag is set and E-flag is not set then PCE MUST consider the 208 protection eligibility as PROTECTION PREFERRED constraint. 210 When L-flag is not set and E-flag is not set then PCE SHOULD consider 211 the protection eligibility as UNPROTECTED PREFERRED but MAY consider 212 protection eligibility as UNPROTECTED MANDATORY constraint. 214 When L-flag is not set and E-flag is set then PCE MUST consider the 215 protection eligibility as UNPROTECTED MANDATORY constraint. 217 For a PCC which does not yet support this draft, the E-flag bit is 218 always set to zero as per [RFC5440] . Therefore, a PCE communicating 219 with a PCC which does not support this draft would treat the L-Flag 220 set as being PROTECTION PREFERRED. 222 The protection constraint can only be applied to resource selection 223 in which the protection state is known to PCE. A PCE calculating a 224 path that includes resources which does not support the protection 225 state being known to PCE (such as Node SID), then the protection 226 state MAY ignore the protection enforcement constraint. 228 UNPROTECTED PREFERRED and PROTECTED PREFERRED may seem similar but 229 they indicate the preference of selection if PCE has an option of 230 either protected or unprotected available for a link. When presented 231 with either option, PCE SHOULD select the SID which has a protection 232 state matching the state of the L-Flag. 234 3. Security Considerations 236 This document clarifies the behaviour of an existing flag and 237 introduces a new flag to provide further control of that existing 238 behaviour. The introduction of this new flag and behaviour 239 clarification does not create any new sensitive information. No 240 additional security measure is required. 242 Securing the PCEP session using Transport Layer Security (TLS) 243 [RFC8253] , as per the recommendations and best current practices in 244 [RFC7525], is RECOMMENDED. 246 4. IANA Considerations 248 4.1. LSP Attributes Protection Enforcement Flag 250 This document defines a new LSP Attribute Flag; IANA is requested to 251 make the following bit allocation from the "LSPA Object" sub registry 252 of the PCEP Numbers registry, as follows: 254 Value Name Reference 256 6 PROTECTION-ENFORCEMENT This document 258 5. Normative References 260 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 261 Requirement Levels", BCP 14, RFC 2119, March 1997. 263 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 264 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 265 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 266 . 268 [RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast 269 Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, 270 DOI 10.17487/RFC4090, May 2005, 271 . 273 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 274 Element (PCE)-Based Architecture", RFC 4655, 275 DOI 10.17487/RFC4655, August 2006, 276 . 278 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 279 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 280 DOI 10.17487/RFC5440, March 2009, 281 . 283 [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, 284 "Recommendations for Secure Use of Transport Layer 285 Security (TLS) and Datagram Transport Layer Security 286 (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 287 2015, . 289 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 290 S. Ray, "North-Bound Distribution of Link-State and 291 Traffic Engineering (TE) Information Using BGP", RFC 7752, 292 DOI 10.17487/RFC7752, March 2016, 293 . 295 [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody, 296 "PCEPS: Usage of TLS to Provide a Secure Transport for the 297 Path Computation Element Communication Protocol (PCEP)", 298 RFC 8253, DOI 10.17487/RFC8253, October 2017, 299 . 301 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 302 Decraene, B., Litkowski, S., and R. Shakir, "Segment 303 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 304 July 2018, . 306 Authors' Addresses 308 Andrew Stone 309 Nokia 311 Email: andrew.stone@nokia.com 313 Mustapha Aissaoui 314 Nokia 316 Email: mustapha.aissaoui@nokia.com