Internet Engineering Task Force Q. Zhao Internet-Draft Huawei Technology Intended status: Standards Track David Amzallag Created: March 4, 2009 BT Expires: September 4, 2009 Daniel King Old Dog Consulting PCE-based Computation Procedure To Compute Shortest Constrained P2MP Inter-domain Traffic Engineering Label Switched Paths draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract Point-to-multipoint (P2MP) Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering Label Switched Paths (TE LSPs) may be established using signaling techniques, but their paths must first be determined. The Path Computation Element (PCE) has been identified as an appropriate technology for the determination of the paths of P2MP TE LSPs. This document describes the procedures and extensions to the PCE communication Protocol (PCEP) to handle requests and responses for the computation of inter-domain paths for P2MP TE LSPs. Zhao, et el. [Page 1] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 Contents 1. Introduction.....................................................3 1.1 Problem Statement.............................................3 1.2 Assumptions...................................................4 1.3 Requirements..................................................4 1.4 Objective Functions...........................................5 2. Terminology......................................................6 3. Procedures.......................................................7 3.1 Per Domain Path Computation...................................7 3.2 Backwards Recursive Path Computation..........................7 3.3 Core Tree Path Computation....................................7 3.3.1 Core Tree Based Procedure.................................7 4. Protocol Extensions for Core Tree Based Computation..............9 4.1 The Extension of RP Object....................................9 4.2 The PCE topology Object......................................10 5. IANA Considerations.............................................11 6. Manageability...................................................11 6.1 Scalability Considerations...................................11 7. Security........................................................11 8. Acknowledgement.................................................11 9. References......................................................12 9.1 Normative References.........................................12 9.2 Informative References.......................................12 10. Authors' Addresses.............................................13 11. Intellectual Property Consideration............................13 12. Disclaimer of Validity.........................................14 13. Full Copyright Statement.......................................14 Zhao, et el. [Page 2] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 1. Introduction Multicast services are increasingly in demand for high-capacity applications such as multicast VPNs, IPTV (on-demand or streaming), and content-rich media distribution (for example, software distribution, financial streaming, or data-sharing). The inter-domain P2MP TE LSP is a feature that facilities the deployment and operation of these services across multi domains. The need to establish point-to-multipoint (P2MP) traffic engineered (TE) Label Switching Paths (LSPs) in Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) networks is covered in [RFC4461]. The applicability of the Path Computation Element (PCE) for the computation of such paths is discussed in [PCE-P2MP-APP], and the requirements placed on PCEP for this are given in [PCE-P2MP-REQ]. The static stitching or RSVP-TE extension based solution might solve the issue in certain degree, but they cannot compute an optimal inter-domain P2MP TE LSP. This document defines a PCE-based solution which will give the optimal inter-domain P2MP TE LSP. 1.1 Problem Statement The Path Computation Element (PCE) defined in [RFC4655] is an entity that is capable of computing a network path or route based on a network graph, and applying computational constraints. A Path Computation Client (PCC) may make requests to a PCE for paths to be computed. [RFC4875] describes how to set up P2MPTE LSPs for use in MPLS GMPLS networks. The PCE is identified as a suitable application for the computation of paths for P2MP TE LSPs [PCE-P2MP-APP]. The draft-ietf-pce-brpc-09.txt specifies a procedure relying on the use of multiple Path Computation Elements (PCEs) to compute point-to- point (P2P) inter-domain shortest constrained paths across a predetermined sequence of domains, using a backward recursive path computation technique. The technique preserves confidentiality across domains, which is sometimes required when domains are managed by different Service Providers. The PCE communication protocol (PCEP) [PCEP] is extended as a communication protocol between PCCs and PCEs for point-to- multipoint(P2MP) path computations and is defined in [PCE-P2MP-EXT]. However, that specification does not provide a mechanism to request path computation of inter-domain P2MP TE LSPs. Zhao, et el. [Page 3] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 This document presents a solution, and procedures and extensions to PCEP to support P2MP inter-domain path computation. 2.2 Assumptions It is assumed that due to deployment and commercial limitations (e.g.,inter-AS peering agreements) the sequence of domains for a path (the path domain tree) will be known in advance. The examples and scenarios used in this document are also based on the following assumptions: - The PCE that serves each domain in the path domain tree is known and the set of PCEs and their relationships is propagated to each PCE during the first exchange of path computation requests; - Each PCE knows about any leaf LSRs in the domain it serves; - The boundary nodes to use on the LSP are pre-determined and form path of the path domain tree. In this version of the document we do not consider multi-homed domains. 1.3 Requirements This section summarizes the PCEP requirements specific to computing inter-domain P2MP paths. In these requirements we note that the actual computation times by any PCE implementation are outside the scope of this document, but we observe that reducing the complexity of the required computations has a beneficial effect on the computation time regardless of implementation. Additionally, reducing the number of message exchanges and the amount of information exchanged willreduce the overall computation time for the entire P2MP tree. We refer to the "Complexity of the computation" as the impact on these aspects of path computation time as various parameters of the topology and the P2MP LSP are changed. 1. The requirements specified in [RFC5376]; 1.1 PCEP must allow an SP to hide from other SPs the set of hops within its own ASes that are traversed by an inter-AS inter-provider TE LSP for each inter-AS TE LSP path segment an inter-AS PCE computes, it may return to the requesting inter-AS PCE an inter-AS TE LSP path segment from its own ASes without detailing the explicit intra-AS hops. Zhao, et el. [Page 4] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 2. The computed P2MP LSP should be optimal when only considering The paths among the BNs. 3. Grafting and pruning of multicast destinations in a domain should have no impact on other domains and on the paths among BNs. 4. The complexity of the computing for each sub-tree within each domain should be only dependent on the topology of the domain and it should be independent of the domain sequences. 5. The number of PCEP request and reply messages should be independent of the number of multicast destinations in each domain. 6. A number of additional requirements have also been identified in [PCE-P2MP-REQ]. 1.4 Objective Functions During the computation of a single or a set of P2MP TE LSPs a request to meet specific optimization criteria, called an Objective Function (OF), may be requested. The computation of one or more P2MP TE-LSPs maybe subject to an OF in order to select the "best" candidate paths. A variety of objective functions have been identified as being important during the computation of inter-domain P2MP LSPs. These are: 1. The sub-tree within each domain should be optimized. 1.1 Minimum cost tree [PCE-P2MP-REQ]. 1.2 Shortest path tree [PCE-P2MP-REQ]. 2. The P2MP LSP paths should be optimal while only considering the entry and exit nodes of each domain as the transit, branch and leaf nodes of the P2MP LSP path. (That is, the Core Tree should be optimized.) 3. It should be possible to limit the number of entry points to a domain. 4. It should be possible to force the branches for all leaves within a domain to be in that domain. Zhao, et el. [Page 5] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 2. Terminology This document uses PCE terminology defined in [RFC4655], [RFC4875], and [PCEP]. Additional terms are defined below and draw on the concepts set out for P2MP LSPs in [RFC4461]. Boundary Nodes: Each Domain has entry LSRs and exit LSRs that can either be ABRs or ASBRs. They are defined here as Boundary Nodes (BNs). Core Tree: The partial P2MP Path Tree with only the BNs added and without the leaf nodes. Leaf Boundary Nodes: The entry boundary node in the leaf domain. Leaf Domain: A domain containing at least one leaf node of the P2MP LSP. (Cf. Bud Domain.) Leaf Nodes: The LSR in any domain which is the P2MP LSP's final destination. (all the light blue nodes) OF: Objective Function: A set of one or more optimization criterion (criteria) used for the computation of a single path (e.g. path cost minimization), or the synchronized computation of a set of paths (e.g. aggregate bandwidth consumption minimization, etc.). See [RFC4655] and [PCE-OF]. Path Domain Sequence: The known sequence of domains for a path. PCE Sequence: The known sequence of PCEs for calcaulting a path. PCE Topology Tree: A list of PCE Sequences which has all the PCE Sequence for each path of the P2MP LSP path tree. Point-to-multipoint Path Tree: A set of LSRs and TE links that comprise the path of a P2MP TE LSP from its ingress LSR to all of its egress LSRs. Root Boundary Node: The egress LSR from the root domain on the path of the P2MP LSP. Root Domain: The domain that includes the ingress (root) LSR. Transit Domain: A domain that has an upstream and downstream neighbour domain. (Cf. Branch Domain and Bud Domain) Zhao, et el. [Page 6] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 4..Procedures 3.1 Per Domain Path Computation Computing P2P LSPs individually is an acceptable solution for computing a P2MP tree. Per domain path computation [RFC5152] can be used to compute P2P multi-domain paths, but does not guarantee to find the optimal path. Furthermore, constructing a P2MP tree from individual source to leaf P2P LSPs does not guarantee to produce a least-cost tree; it does produce a least-cost-to-destination tree. This approach may be considered to have scaling issues during LSP setup. That is, the LSP to each leaf is signaled separately, and each border node must perform path computation for each leaf possibly invoking a PCE (although it may re-use path fragments already used for other leaves if this information is retained in a stateful PCE). 3.2 Backwards Recursive Path Computation Backward recursive path computation (BRPC) [BRPC] provides a mechanism to compute optimal P2P LSPs. This overcomes one of the issues raised in Section 3.1, but nevertheless, a P2MP tree constructed from individually computed optimal P2P LSPs does not guarantee to produce a least-cost tree; it does produce a least-cost- to-destination tree. This approach may have scaling issues during path computation as each the path to each leaf must be computed separately. Although path fragments already used for other leaves may be re-used by stateful PCEs, the information must still be transmitted in a full exchange of PCEP messages for each leaf. 3.3.1 Core Tree Based Path Computation A core tree based solution provides an optimal inter-domain P2MP TE LSP and meets the requirements and OFs outlined in previous sections. A core tree is a path tree with nodes from each domain corresponding to the PCE topology which satisfies the following conditions: - The root of the core tree is the ingress LSR in the root domain; - The leaf of the core tree is the entry node in the leaf domain; - The transit and branch node are from the entry and exit nodes from the transit and branch domains. Zhao, et el. [Page 7] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 Computing the complete P2MP LSP path tree is done in two phases: Procedure Phase 1: P2MP LSP Core Tree Building for the Boundary Nodes (BNs). Procedure Phase 2: Grafting destinations to the P2MP LSP Core Tree. Once the core tree based inter-domain tree is built. The grafting of all the leaf nodes from each domain to the core tree can be achieved. The algorithms to compute the optimal large core tree are outside scope of this document. In the case that the number of domains and the number of BNs are not big, the following BRPC based procedure can be used to compute the core tree. BRPC Based CoreTree Path Computation Procedure 1. Using the BRPC procedures to compute the VSPT(i) for each BN(i), i=1 to n, where n is the total number of entry nodes for all the leaf domains. In each VSPT(i), there are number of P(i) paths. 2. When the root PCE has computed all the VSPT(i), i=1 to n, take one path from each VSPT and form a set of paths, we call it a PathSet(j), j=1 to M, where M=P(1)xP(2)...xP(n); 3. For each PathSet(j), there are n paths and form these n paths into a CoreTree(j); 4. There will be M number of CoreTrees computed from step3. Apply the OF to each of these M CoreTrees and find the optimal CoreTree according to the OF. Zhao, et el. [Page 8] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 4. Protocol Extensions for Core Tree Based Computation The following section describes the protocol extensions for Core Tree based inter-domain P2MP path calculation. 4.1 The Extension of RP Object The extended format of the RP object body to include the C bit as follows: 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags |C|O|B|R| Pri | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Request-ID-number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // Optional TLV(s) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: RP Object Body Format The following flags are added in this draft: C ( P2MP Inter-domain core tree bit - 1 bit): 0: This indicates that the message is for the normal leaf grafting/pruning; 1: This indicates that the request associated with this RP is core tree computation request or reply Zhao, et el. [Page 9] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 4.2. The PCE Sequence Object The PCE Sequence Object is added to the existing PCE protocol. A list of this objects will represent the PCE topology tree. A list of Sequence Objects can be exchanged between PCEs during the PCE capability exchange or on the first path computation request message between PCEs. In this case, the request message format needs to changed to include the list of PCE Sequence Objects for the PCE inter-domain P2MP calculation request. Each PCE Sequence is can be obtained from the domain sequence for a specific path. All the PCE sequences for all the paths of P2MP inter-domain form the PCE Topology Tree of the P2MP LSP. The format of the new PCE Sequence Object for IPv4 (Object-Type 3) is as follows: 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Object-Class | OT |Res|P|I| Object Length (bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 address for root PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 address for the downstream PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 address for the downstream PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | !! | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 address for the PCE corresponding to the leafDomain | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: The New PCE Sequence Object Body Format for IPv4 The format of the new PCE Sequence Object for IPv6 is as follows: 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Object-Class | OT |Res|P|I| Object Length (bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 address for root PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 address for the downstream PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv6 address for the downstream PCE | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | !! | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 address for the PCE corresponding to the leafDomain | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: The New PCE Sequence Object Body Format for IPv6 Zhao, et el. [Page 10] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 5. IANA Considerations A number of IANA considerations have been highlighted in the relevant sections of this document. Further clarifications of these requests will be made in a future version of this document. 6. Manageability TBD in a future version of the draft. 6.1 Scalability Considerations TBD in a future version of the draft.] 7. Security TBD in a future version of the draft. 8. Acknowledgement The authors would like to thank Adrian Farrel for his valuable comments on this draft. 9. References 9.1. Normative References [RFC5152] Vasseur, J.P., Ed., Ayyangar, A., Ed., and R. Zhang, "A Per-domain path computation method for computing Inter-domain Traffic Engineering (TE) Label Switched Path (LSP)", [BRPC] J.P. Vasseur, Editor, "A Backward Recursive PCE-based Computation (BRPC) procedure to compute shortest inter-domain Traffic Engineering Label Switched Paths", draft-ietf-pce-brpc, work in progress. [PCEP] Ayyangar, A., Farrel, A., Oki, E., Atlas, A., Dolganow, A., Ikejiri, Y., Kumaki, K., Vasseur, J., and J. Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", draft-ietf-pce-pcep-19 (work in progress), Novemeber 2008. Zhao, et el. [Page 11] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 [PCE-OF] Le Roux, J.L., Vasseur, J.P., and Lee, Y., "Encoding of Objective Functions in Path Computation Element communication Protocol (PCEP)", draft-ietf-pce-of, work in progress. 9.2 Informative References [RFC4461] S. Yasukawa, Editor, "Signaling Requirements for Point-to-Multipoint Traffic Engineered MPLS LSPs", RFC4461, April 2006. [RFC5376] Bitar, N., Zhang, R,. Kumaki, K,. "Inter-AS Requirements for the Path Computation Element Communication Protocol (PCECP)", RFC 5376, November 2008. [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006. [RFC4875] Aggarwal, R., Papadimitriou, D., and Yasukawa, S., "Extensions to Resource Reservation Protocol - Traffic Engineering (RSVP-TE) for Point-to-Multipoint TE Label Switched Paths (LSPs)", RFC 4875, May 2007. [PCE-P2MP-REQ] Yasukawa, S. and A. Farrel, "PCC-PCE Communication Requirements for Point to Multipoint Multiprotocol Label Switching Traffic Engineering (MPLS-TE)", draft-yasukawa-pce-p2mp-req-05 (work in progress), May 2008. [PCE-P2MP-APP] Yasukawa, S. and A. Farrel, "draft-ietf-pce-p2mp-app-01.txt", draft-ietf-pce-p2mp-app (work in progress), Feb 2009. [PCE-P2MP-EXT] Takeda, T., Chaitou M., Le Roux, J.L., Ali Z., Zhao, Q., King, D., "draft-ietf-pce-pcep-p2mp-extensions-01,work in progress, October , 2008. Zhao, et el. [Page 12] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 10. Authors' Addresses Quintin Zhao Huawei Technology 125 Nagog Technology Park Acton, MA 01719 US Email: qzhao@huawei.com David Amzallag British Telecommunications plc Email: david.amazallag@bt.com Daniel King Old Dog Consulting Email: daniel@olddog.co.uk 11. Intellectual Property Consideration The IETF Trust takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in any IETF Document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Copies of Intellectual Property disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement any standard or specification contained in an IETF Document. Please address the information to the IETF at ietf-ipr@ietf.org. The definitive version of an IETF Document is that published by, or under the auspices of, the IETF. Versions of IETF Documents that are published by third parties, including those that are translated into other languages, should not be considered to be definitive versions of IETF Documents. The definitive version of these Legal Provisions is that published by, or under the auspices of, the IETF. Versions of these Legal Provisions that are published by third parties, including those that are translated into other languages, should not be considered to be definitive versions of these Legal Provisions. Zhao, et el. [Page 13] draft-zhao-pce-pcep-inter-domain-p2mp-procedures-00.txt March 2009 For the avoidance of doubt, each Contributor to the IETF Standards Process licenses each Contribution that he or she makes as part of the IETF Standards Process to the IETF Trust pursuant to the provisions of RFC 5378. No language to the contrary, or terms, conditions or rights that differ from or are inconsistent with the rights and licenses granted under RFC 5378, shall have any effect and shall be null and void, whether published or posted by such Contributor, or included with or in such Contribution. 12. Disclaimer of Validity All IETF Documents and the information contained therein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 13. Full Copyright Statement Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Zhao, et el. [Page 14]