Relayed CSPF for Multi-Area Multi-AS PCE draft-lu-relayed-cspf-00.txt

1. Relayed CSPF for Multi-Area Multi-AS PCEdraft-lu-relayed-cspf-00.txt IETF 79 - Beijing, China November 7-12, 2010 Wenhu Lu, SriganeshKini, Srikanth Narayanan

2. Agenda • Solutions analysis • CSPF seed, heap, and relay • Mathematical base • PCE Elect • PCEP Extension • Relay Timer • Multi-AS

3. Existing Solutions • Global TED • Too big, negating the purpose of having multiple areas or ASes; • violates the information hiding and confidentiality requirement and is unacceptable by ISPs • Crankback • Not scale • Not optimal • Labor intensive • RBPC – RFC5441 • Assume tailend is location-known, not always true • Can’t handle multi-homed cases • Complexity - Virtual Shortest Path Tree (VSPT)

4. We look for • Solutions with • optimality • Scalability • simplicity

5. Divide & Conquer • Path Tree Path Trees Headend Headend Area-1 Global TED Area-2 Area-3 Tailend Tailend

6. CSPF Seed • The initial node for CSPF, or SPF • Seed to the heap • SPF is a seed based algorithm • The entire Shortest Path Tree (SPT) is built upon this seed.

7. Multiple Seeds • A heap can have >1 seeds • In SPF expansion, the heap contains many nodes • can be perceived as seeds for further expansion.

8. Heap Equivalence • A heap with one initial seed • is equivalent to that with multiple intermediate seeds in any SPF stages for the destinations that have not yet been reached. • The deposit time of seeds • is insensitive to destinations that have not yet been reached, provided that the seeds carry correct attributes values such as cost and nexthop. • The multiple seeds in property 1 • can further be reduced to those that constitute a set of nodes besides which the destinations are not viable.

9. Simple Case • For convenience, assume every router is also a PCE • Start from Area “North” where Headend “H” resides • Compute paths to “A” and “B” • Note that “C” is not used • PCE-North sends “relay” request to PCE-South, say “B” • PCE-South uses “A” and “B” as seeds for CSPF in area “South” • Note that “A” and “B” have non-zero initial cost, hop-count, etc. • These two seeds will be the base to reach tailend “T” • PCE-South replys to PCE-North which stitch the paths H C North A B T South

10. PCE Elect • For an exit area • Only one BN is necessary • Either “A” or “B” will work • Can be achieved through IGP-TE extension • draft-lu-ospf-area-tlv-00.txt

11. Multi-Exit-Areas • Two paths avaible • Race condition B A D PCRep D B H PCReq T PCReq E A PCRep C C F

12. Relay Timer • To collect multiple PCRep • Timeout to avoid infinite wait

13. PCEP Seed TLV 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Len | Node-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Node-ID (Cont) | Sub-Type | Sub-Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Seg-ID | Cost | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Cost (Cont) | Hops | Sub-Type | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-Type #1 | | | // // | Sub-Type #M | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

14. Multi-AS Path Computation • Information Hiding • Loose EROs • Loose ERO recovery method • Pre-computed EROs • Re-Query • Transit Link • Included in the seed attributes

15. Thank You