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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Seisho Yasukawa 2 Internet Draft NTT 3 Category: Informational Adrian Farrel 4 Expires: August 2006 Old Dog Consulting 5 February 2006 7 PCC-PCE Communication Requirements for Point to Multipoint 8 Traffic Engineering 10 draft-yasukawa-pce-p2mp-req-00.txt 12 Status of this Memo 14 By submitting this Internet-Draft, each author represents that any 15 applicable patent or other IPR claims of which he or she is aware 16 have been or will be disclosed, and any of which he or she becomes 17 aware will be disclosed, in accordance with Section 6 of BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as 22 Internet-Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 Abstract 37 The Path Computation Element (PCE) provides functions of path 38 computation in support of traffic engineering in Multi-Protocol Label 39 Switching (MPLS) and Generalized MPLS (GMPLS) networks. 41 Extensions to the MPLS and GMPLS signaling and routing protocols have 42 been made in support of traffic engineered point-to-multipoint (P2MP) 43 label switched paths (LSPs). Since P2MP LSP routes are sometimes 44 complex to compute, and given the use of PCE in MPLS networks it is 45 likely that PCE will be used in P2MP MPLS networks. 47 Generic requirements for a communication protocol between Path 48 Computation Clients (PCCs) and PCEs are presented in "PCE 49 Communication Protocol Generic Requirements". This document 50 complements the generic requirements and presents a detailed set of 51 PCC-PCE communication protocol requirements for point-to-multipoint 52 traffic engineering. 54 Conventions used in this document 56 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 57 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 58 document are to be interpreted as described in RFC 2119 [RFC2119]. 60 1. Introduction 62 The Path Computation Element (PCE) defined in [PCE-ARCH] is an entity 63 that is capable of computing a network path or route based on a 64 network graph, and applying computational constraints. The intention 65 is that the PCE is used to compute the path of traffic engineered 66 label switched paths (TE LSPs) within Multiprotocol Label Switching 67 (MPLS) and Generalized MPLS (GMPLS) networks. 69 Requirements for point-to-multipoint (P2MP) MPLS TE LSPs are 70 documented in [P2MP-REQ] and signaling protocol extensions are 71 defined in [P2MP-RSVP]. P2MP MPLS TE networks are currently being 72 planned by service provides in support of various features including 73 layer 3 multicast VPNs. 75 Path computation for P2MP LSPs presents a significant challenge and 76 network optimization of multiple P2MP TE LSPs will require 77 considerable computational resources. PCE offers a way to offload 78 such path computations from LSRs. 80 The applicability of the PCE-based path computation architecture to 81 point-to-multipoint MPLS traffic engineering is described in a 82 companion document [PCE-P2MP-APP]. No further attempt is made to 83 justify the use of PCE for P2MP MPLS TE within this document. 85 This document presents a set of PCC-PCE communication protocol 86 (PCECP) requirements for P2MP MPLS traffic engineering. It 87 supplements the generic requirements documented in [PCE-COM-REQ]. 89 2. PCC-PCE Communication Requirements for P2MP MPLS Traffic Engineering 91 This section sets out additional requirements not covered in 92 [PCE-COM-REQ] specific to the problems of P2MP MPLS TE. 94 2.1. PCC-PCE Communication 96 The PCC-PCE communication protocol MUST allow requests and replies for 97 the computation of paths for P2MP LSPs. 99 This requires no additional messages, but implies the following 100 additional constraints to be added to the PCC-PCE communication 101 protocol. 103 2.1.1. Indication of P2MP Path Computation Request 105 Although the presence of certain parameters (such as a list of more 106 than one destination) may be used to infer that a path computation 107 request is for a P2MP LSP, an explicit parameter SHOULD be placed in 108 a conspicuous place within a Path Computation Request message to 109 allow a receiving PCE to easily identify that the request is for a 110 P2MP path. 112 2.1.2. Non-Support of P2MP Path Computation 114 Not all PCEs are required to support P2MP path computation. Therefore 115 it MUST be possible for a PCE to reject a P2MP Path Computation 116 Request message with a reason code that indicates no support for P2MP 117 path computation. 119 2.1.3. Non-Support by Back-Level PCE Implementations 121 It is possible that initial PCE implementations will be developed 122 without support for P2MP path computation and without the ability to 123 recognize the explicit flag described in section 2.1.1. Therefore at 124 least one parameter required for P2MP path computation (possibly 125 including the flag described in section 2.1.1) MUST be defined in 126 such a way as to cause automatic rejection as unprocessable or 127 unrecognized by a back-level PCE implementation without requiring any 128 changes to that PCE. 130 2.1.4. Specification of Destinations 132 Since P2MP LSPs have more than one destination, it MUST be possible 133 for a single Path Computation Request to list multiple destinations. 135 2.1.5. Indication of P2MP Paths 137 The Path Computation Response MUST be able to carry the path of a 138 P2MP LSP. This SHOULD be expressed as a compacted series of routes as 139 described in [P2MP-RSVP] although not necessarily using an identical 140 encoding. This MAY be expressed as a non-compacted series of 141 source-to-destination routes. 143 2.1.6. Multi-Message Requests and Responses 145 A single P2MP LSP may have very many destinations, and the computed 146 path (tree) may be very extensive. In these cases it is possible that 147 the entire Path Computation Request or Response cannot fit within one 148 PCE message. Therefore it MUST be possible for a single request or 149 response to be conveyed by a sequence of messages. 151 Note that there is a requirement in [PCE-COM-REQ] for reliable and 152 in-order message delivery, so it is assumed that components of the 153 sequence will be delivered in order and without missing items. 155 2.1.7. Non-Specification of Per-Destination Constraints and Parameters 157 It MUST NOT be possible to set different constraints, traffic 158 parameters, or quality of service requirements for different 159 destination of a P2MP LSP within a single computation request. 161 2.1.8. Path Modification and Path Diversity 163 No changes are made to the requirement to support path modification 164 and path diversity as described in [PCE-COM-REQ]. Note, however, that 165 a consequence of this requirement is that it must be possible to 166 supply an existing path on a Path Computation Request. This 167 requirement is unchanged as well, but it is a new requirement that 168 such paths MUST be able to be P2MP paths. 170 2.1.9. Capabilities Exchange 172 PCE capabilities exchange forms part of PCE discovery [PCE-DISCO], 173 but MAY also be included in the PCECP message exchanges. 175 In the event that the PCE ability to perform P2MP computation is not 176 advertised as part of PCE discovery, the PCECP MUST allow a PCC to 177 discover which PCEs with which it communicates support P2MP path 178 computation and which objective functions specific to P2MP path 179 computation are supported by each PCE. 181 3. Manageability Considerations 183 Manageability of P2MP MPLS TE with PCE must address the following 184 considerations. 186 - Need for a MIB module for control and monitoring. 187 - Need for built-in diagnostic tools. 188 - Configuration implications for the protocol. 190 4. Security Considerations 192 P2MP computation requests do not raise any additional security issues 193 for the PCECP. 195 Note, however, that P2MP computation requests are more CPU-intensive 196 and also use more link bandwidth. Therefore if the PCECP was 197 susceptible to denial of service attacks based on the injection of 198 spurious Path Computation Requests, the support of P2MP path 199 computation would exacerbate the effect. 201 It would be possible to consider applying different authorization 202 policies for P2MP path computation requests compared to other 203 requests. 205 5. IANA Considerations 207 This document makes no requests for IANA action. 209 6. Acknowledgments 211 TBD 213 7. References 215 7.1. Normative Reference 217 [RFC2119] Bradner, S., "Key words for use in RFCs to indicate 218 requirements levels", RFC 2119, March 1997. 220 [PCE-COM-REQ] J. Ash, J.L Le Roux et al., "PCE Communication 221 Protocol Generic Requirements", 222 draft-ietf-pce-comm-protocol-gen-reqs (work in 223 progress). 225 7.2. Informative Reference 227 [PCE-ARCH] A. Farrel, JP. Vasseur and J. Ash, "Path Computation 228 Element (PCE) Architecture", 229 draft-ietf-pce-architecture (work in progress). 231 [PCE-DISCO] JL Le Roux et al., "Requirements for Path Computation 232 Element (PCE) Discovery", 233 draft-ietf-pce-discovery-reqs (work in progress). 235 [PCE-P2MP-APP] S. Yasukawa et al., "Applicability of the Path 236 Computation Element to Point-to-Multipoint Traffic 237 Engineering", draft-yasukawa-pce-p2mp-app, (work in 238 progress). 240 [P2MP-REQ] Yasukawa, S. (Editor), "Signaling Requirements for 241 Point to Multipoint Traffic Engineered MPLS LSPs", 242 draft-ietf-mpls-p2mp-sig-requirement, (work in 243 progress). 245 [P2MP-RSVP] Aggarwal, R., Papadimitriou, D., and Yasukawa, S., 246 "Extensions to RSVP-TE for Point to Multipoint TE 247 LSPs", draft-ietf-mpls-rsvp-te-p2mp, (work in 248 progress). 250 8. Authors' Addresses 252 Seisho Yasukawa 253 NTT 254 3-9-11 Midori-cho, 255 Musashino-shi, Tokyo 180-8585, Japan 256 Email: yasukawa.seisho@lab.ntt.co.jp 258 Adrian Farrel 259 Old Dog Consulting 260 Email: adrian@olddog.co.uk 262 9. 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