On 01/09/2017 02:45 PM, Jonathan Hardwick wrote: > Hi Aaron Hello Jon,
> Thanks. So actually, I need to backtrack and agree that there is a mechanism > defined for a backup PCE to request that an orphaned LSP is delegated to it - > I had missed that. > > I am not sure that this implies that the PCC cannot re-delegate of its own > free will. It would be useful to have that clarified in the draft. Note that Redelegation Timeout Interval is a PCC-local value, which the PCC can alter dynamically based on its internal state at any moment (as per pce-stateful-pce section 2). pce-stateful-pce does not change the fact that the PCC is in control over an LSP's state. With pce-pce-initiated-lsp the set of options available to a PCC with respect to having a say in LSP's shape, form and existence is limited and involves trade-offs, but at the end of the day PCC can always assume control of an LSP. Specifically it can (without implying it should) legally execute the following sequence based solely on its local policy: 1) terminate the PCEP session with the primary PCE 2) reduce Redelegation Timeout Interval to 0, effectively expiring it 3) delegate the (now orphan) LSP to a currently-connected backup PCE 4) restore Redelegation Timeout Internal back to normal Step 3 can alternatively involve reducing State Timeout Interval, at which point the PCC is in complete control of the LSP (can delete it or revert it to operator-defined default per section 2). > However, given this mechanism exists, it does raise the question about how > PCEs should properly cooperate in terms of how orphaned LSPs are detected and > who should request ownership. pce-stateful-pce was designed with PCC being central authority over LSP state and how it relates to connected PCEs. With pce-pce-initiated-lsp there are multiple options how a set of redundant PCEs can be realized. It may also involve a lot complex implementation-specific trade-offs, for example in load-balancing, hence we chose to leave inter-PCE arbitration out of scope. As outlined above, a PCC implementation with a sufficiently smart local policy can still act as a coordinator, although quite a limited one. Regards, Robert
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