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

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 TechnologyZafar Ali, Cisco Systems

Tarek Saad, Cisco SystemsFabien Verhaeghe, Thales Communication

Daniel King, Old Dog ConsultingKenji Kumaki, KDDIDavid 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 RFC4461

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

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PCE4

PCE3

PCE1 PCE5PCE6

PCE7

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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 tree6

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D1

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PCE4

PCE(4) computes path XVSPT(4)

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Extended BRPC – Phase 1, step 1

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PCE(3) computes path XVSPT(3) using XVSPT(4)

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Extended BRPC Phase 1, step 2

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PCE(2) computes path XVSPT(2) using XVSPT(3)

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Extended BRPCPhase 1, step 3

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PCE(1) composes the aggregate P2MP tree from information collected

BN20, BN26 not considered

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PCE2

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PCE1

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Extended BRPCPhase 1, step 4

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• 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 TreeTwo phased approach

76th IETF Hiroshima

Domain1

Domain2

Domain3

Domain4

Domain5

Domain6

Core TreePhase 1: Build the core tree

76th IETF Hiroshima

PCE2

PCE1

PCE3

PCE4

PCE5

PCE6

T

U

A

EMP

RQ

W

X

ZD1

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 TreePhase 2: Graft destinations

76th IETF Hiroshima

PCE2

PCE1

PCE3

PCE4

PCE5

PCE6

T

U

A

EMP

RQ

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X

ZD1

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