Quintin Zhao, Huawei Technology Zafar Ali, Cisco Systems Tarek Saad, Cisco Systems

1. PCE-based Computation Procedure To Compute Shortest Constrained P2MP Inter-domain Traffic Engineering Label Switched Pathsdraft-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

2. 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

3. 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 RFC4461

4. 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

5. 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

6. PCE2 PCE3 PCE4 BN18 D2 G BN16 BN19 BN24 C BN23 J D1 D BN17 BN20 BN26 BN15 H BN22 BN21 BN1 BN13 PCE5 BN5 PCE1 PCE6 E S BN2 BN6 BN12 BN4 F B D3 D6 BN11 BN7 BN9 BN10 PCE7 I D4 D5 Extended BRPC • 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

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

8. Extended BRPC Phase 1, step 2 PCE3 PCE4 BN18 D2 BN16 BN19 BN24 C BN23 D1 D BN17 BN20 BN26 H BN22 BN21 BN13 BN5 BN20, BN26 not considered PCE(3) computes path XVSPT(3) using XVSPT(4)

9. Extended BRPCPhase 1, step 3 PCE2 PCE3 PCE4 BN18 D2 G BN16 BN16 BN19 BN24 C BN23 D1 D BN17 BN20 BN26 BN15 H BN22 BN21 BN1 BN13 BN5 PCE1 BN20, BN26 not considered PCE(2) computes path XVSPT(2) using XVSPT(3)

10. Extended BRPCPhase 1, step 4 PCE2 PCE3 PCE4 BN18 D2 G BN16 BN16 BN19 BN24 C BN23 D1 D BN17 BN20 BN26 BN15 H BN22 BN21 BN1 BN13 BN5 PCE1 BN20, BN26 not considered S PCE(1) composes the aggregate P2MP tree from information collected 10

11. Extended BRPC Phase 2 BN18 D2 G BN16 BN19 BN24 C D1 D BN15 BN22 BN21 BN1 BN13 BN5 PCE1 E S BN2 BN6 BN12 BN4 F B D3 D6 BN11 BN7 BN9 BN10 • 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) I D4 D5 11

12. 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

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

14. Core Tree Phase 1: Build the core tree PCE4 PCE1 D1 PCE3 T A W E • 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 P M Q R PCE5 X PCE2 Z U D2 PCE6 76th IETF Hiroshima

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

16. 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