PCE-based Computation Procedure To Compute Shortest Constrained P2MP Inter-domain Traffic Engineering Label Switched Paths draft-zhao-pce-pcep-inter-domain-p2mp-procedures-02.txt Quintin Zhao, Huawei Technology Zafar Ali, Cisco Systems Tarek Saad, Cisco Systems Fabien Verhaeghe, Thales Communication Daniel King, Old Dog Consulting Kenji Kumaki, KDDI David Amzallag, BT 76th IETF Hiroshima

History This work describes extensions to the PCE communication Protocol (PCEP) to handle requests and responses for the computation of inter-domain paths for P2MP TE LSPs. Two solutions presented at the IETF74 meeting – draft-ali-pce-brpc-p2mp-ext-00 – draft-zhao-pce-pcep-inter-domain-p2mp-00 Co-chairs requested authors of both drafts communicate to determine if both drafts need to move forward independently, or might be merged draft-zhao-pce-pcep-inter-domain-p2mp-procedures-02 is a merged version of both initial drafts 76th IETF Hiroshima

Requirements Allow a a P2MP TE LSP to meet specific OFs (SPT, MCT) The Sub-tree within each domain should also be optimized subject to the OFs Computing each sub-tree is independent of the domain sequences End-to-end Path has to be remerge free Maintain internal domain confidentiality Grafting and pruning of multicast destinations in a domain should have minimal or no impact on the tree in other domains Limits the number of entry and exit points to a domain A number of additional requirements are also specified in [RFC5376] and RFC4461RFC5376RFC4461

Mechanisms Available Per Domain – Suited for simply-connected domains and where the preferred points of interconnection are known Extended BRPC – Reuses existing techniques and suitable for multi-domain environments with few interconnection points Core Tree – Uses BRPC for its initial phase and utilizes additional techniques to support multi-domain environments with many interconnection points and allows for tree reoptimization

Extended BRPC BRPC is extended so that VSPT also includes Shortest Paths (SPs) from: – Destination (leaf) to all exit BNs in the destination domain – From all entry-BNs to all exit-BNs at every transit domain – Can optimize by excluding entry-BNs and their sub-trees – Forms a virtual graph G(V,E), V={root, BNs, and destinations} and E={aggregate links, inter-domain links} – Runs a suitable spanning tree (ST) heuristic to compute the tree when VSPTs for all destinations are back By clustering requests of destinations, belonging to the same destination domain, performance could be improved

Extended BRPC BN19 C S D BN23 BN22BN21 BN13 BN5 BN1 BN9 BN7 BN6BN12 BN4 BN2 I BN10 BN11 B F E D2 D4 D3 BN24 D1 H D5 BN26 BN20 PCE4 PCE3 PCE1 PCE5 PCE6 PCE7 BN16 J BN15 BN17 PCE2 BN18 G D6 2 Phased approach Phase 1: PCE (1) collects XVSPTs for each of the P2MP destinations Phase 2: using the aggregated tree, PCE(1), computes the P2MP tree 6

BN19 BN24 D1 H BN26 BN20 PCE4 PCE(4) computes path XVSPT(4) 7 Extended BRPC – Phase 1, step 1

BN19 C D BN23 D2 BN24 D1 H BN26 BN20 PCE4 PCE3 BN16 BN17 BN18 PCE(3) computes path XVSPT(3) using XVSPT(4) BN20, BN26 not considered BN22BN21 BN13 BN5 8 Extended BRPC Phase 1, step 2

BN19 C D BN23 D2 BN24 D1 H BN26 BN20 PCE4 PCE3 BN16 BN17 BN18 PCE(2) computes path XVSPT(2) using XVSPT(3) BN20, BN26 not considered BN22BN21 BN13 BN5 BN1 PCE1 BN16 BN15 PCE2 G 9 Extended BRPC Phase 1, step 3

BN19 C D BN23 D2 BN24 D1 H BN26 BN20 PCE4 PCE3 BN16 BN17 BN18 10 PCE(1) composes the aggregate P2MP tree from information collected BN20, BN26 not considered BN22BN21 BN13 BN5 BN16 BN15 PCE2 G S PCE1 BN1 10 Extended BRPC Phase 1, step 4

BN19 C S D BN22BN21 BN13 BN5 BN1 BN9 BN7 BN6BN12 BN4 BN2 I BN10 BN11 B F E D2 D4 D3 BN24 D1 D5 PCE1 BN16 BN15 BN18 G D6 11 PCE(1) completes the aggregate P2MP tree from information collected in XVSPTs for destinations D1,.. D5 PCE(1) runs a P2MP Tree computation based on the aggregated tree PCE(1) replies with P2MP tree to PCC(S) 11 Extended BRPC Phase 2

Core Tree A Core Tree is a path tree with Boundary Nodes (BNs) 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 A Sub-Tree is a path tree within a domain with all of its root node, transit node and leaf node from the same domain The sub-tree within each domain is optimized subject to the OF The Computing each sub-tree is independent of the domain sequences The grafting and pruning of multicast destinations in a domain has no impact on other domains and no impact on the core-tree 76th IETF Hiroshima

Core Tree Two phased approach 76th IETF Hiroshima Domain1 Domain2 Domain3 Domain4 Domain5 Domain6

Core Tree Phase 1: Build the core tree 76th IETF Hiroshima PCE2 PCE1 PCE3 PCE4 PCE5 PCE6 T U A E MP RQ W X Z D1 D2 P2MP LSP Core Tree Building for the Boundary Nodes (BNs) Based on BRPC procedure, builds a VSPT which has the egress as the root and the ingress as the leaf The source PCE builds all possible Core Trees based on the VSPT computed from previous step and find out the optimal Core-Tree based on the OF

Core Tree Phase 2: Graft destinations 76th IETF Hiroshima PCE2 PCE1 PCE3 PCE4 PCE5 PCE6 T U A E MP RQ W X Z D1 D2 Grafting destinations or the sub-trees in each domain to the P2MP LSP Core Tree computed from phase1

Summary & Next Steps Both mechanisms were presented at iPOP 2009 (Tokyo) and MPLS 2009 (Washington) A lot of common ground exists between both mechanisms Lots of work and analysis ahead. We would appreciate feedback on both solutions from the WG We will continue to review requirements and select the technique that best meets the requirements Authors would like the draft to become a WG document 76th IETF Hiroshima