draft-litkowski-pce-state-sync-00 S. Litkowski, Orange S. Sivabalan, Cisco IETF 97 Seoul

Goal PCE Redundancy specification for stateful PCE is really basic today and causes some trouble Association based constraint (like diversity) does not work properly in a redundancy scenario We want to enhance computation and resiliency for association based constraint

Problem to be solved: case 1 Sequence of Events: Configure PCC1->PCC2 ERO used: R1->R3->R4->R2->PCC2 Configure PCC3->PCC4 Need to move the other LSP to find a room PCE2 cannot move the existing LSP No disjointness can be found

Problem to be solved: case 2 Sequence of Events: Configure both LSPs in the same time window A computation loop will occur

Problem to be solved: case 2 PCC3->PCC4 path: R3->R1->PCC2->PCC4 Received PCC1->PCC2 path: none PCC1->PCC2 path: R1->PCC2 Received PCC3->PCC4 path: none

Problem to be solved: case 2 PCC3->PCC4 path: R3->R1->PCC2->PCC4 Received PCC1->PCC2 path: R1->PCC2 PCC1->PCC2 path: R1->PCC2 Received PCC3->PCC4 path: R3->R1->PCC2->PCC4 Non disjoint path Non disjoint path Newly computed paths are reported => disjointness must be computed !

Problem to be solved: case 2 PCC3->PCC4 path: R3->PCC4 Received PCC1->PCC2 path: R1->PCC2 PCC1->PCC2 path: ->PCC2 Received PCC3->PCC4 path: R3->R1->PCC2->PCC4 Disjoint path Disjoint path New paths have been computed, report will be done

Problem to be solved: case 2 PCC3->PCC4 path: R3->PCC4 Received PCC1->PCC2 path: ->PCC2 PCC1->PCC2 path: ->PCC2 Received PCC3->PCC4 path: R3->PCC4 Non disjoint path Non optimal disjoint path Newly computed paths are reported => CSPF will run again to provide a more optimal LSP placement

Problem to be solved: case 2 PCC3->PCC4 path: R3->R1->PCC2->PCC4 Received PCC1->PCC2 path: ->PCC2 PCC1->PCC2 path: R1->PCC2 Received PCC3->PCC4 path: R3->PCC4 We are back to the initial state, as PCE computations are not synchronized , there is a chance that they do not use the right state

Problem to be solved: case 3 Having a single PCE in a network may be dangerous: We never put all eggs in one basket But how to handle disjointness-like computation in this scenario:

Our proposal InterPCE communication is required ! Let’s create a stateful PCEP session between PCEs It is not specified by any document yet Using multiple computing PCEs for association based constraint is not a good idea: Let’s introduce a master/slave mechanism Using subdelegation

State-sync session We use a new bit flag in the STATEFUL-CAPABILITY-TLV: STATE-SYNC-CAPABILITY At session opening stage, both PCEs behaves both as PCC and PCE: bidirectional initial synchronization is used Each PCE will report its delegated LSPs on the state-sync session and may decide to subdelegate to a master PCE PCE1 PCRpt S=1 PCE2 PCC PCRpt EOS PCRpt S=1 PCRpt EOS PCRpt D=1 PCupdate PCupdate PCRpt D=1 PCRpt D=1

Master/slave PCE Master/slave PCE is based on a priority mechanim How to exchange priority is out of scope of the document It may be an IGP/BGP extension, local configuration, … A PCE may be master for some LSPs or associations and slave for others (loadsharing) If a PCE does not have delegation for all LSPs in the association, it should not take into account the association constraint or provide no-path.

Back to problem case 2 PCE1 is master for the association Received PCC3->PCC4 path: none Received PCC1->PCC2 path: PCC1->PCC2 path: R1->PCC2 PCC3->PCC4 path: none PCRpt D=1 PCC3->PCC4 PCE1 computes path for PCC1->PCC2 (delegated by PCE) PCE2 subdelegates PCC3->PCC4 to PCE1

Back to problem case 2 Received PCC3->PCC4 path: PCRpt D=0 PCC1->PCC2 Received PCC3->PCC4 path: R3->R1->PCC2->PCC4 Received PCC1->PCC2 path: R1->PCC2 PCC1->PCC2 path: R1->PCC2 PCC3->PCC4 path: R3->R1->PCC2->PCC4 PCUpd D=1 PCC3->PCC4 Disjoint path PCE1 computes path for PCC3->PCC4 and updates PCE2 It reports also PCC1->PCC2 path to PCE2

Conclusion and next steps State-sync provides an efficient way to design a network using PCEP It offers possibility to loadshare computation while keeping optimal computation without risk of loops It increases the resiliency of the design It provides a good scaling solution for PCE It does not touch the PCC side (easier and faster to deploy) We have some running code… (to be deployed soon) We welcome feedback from the WG