Re: [Pce] draft-ietf-pce-pce-initiated-lsp

[Jonathan Hardwick <[e-mail]>]

Hi Aaron

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.

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.  I know that there is work ongoing in the following draft which discusses co-operation between redundant PCEs.  I am not sure whether your idea is best discussed in the context of that draft or in draft-ietf-pce-pce-initiated-lsp.  Perhaps the authors could chime in?
https://tools.ietf.org/id/draft-litkowski-pce-state-sync-00.txt

Best regards
Jon


-----Original Message-----
From: Aaron Itskovich [mailto:[e-mail]] 
Sent: 05 January 2017 19:30
To: Jonathan Hardwick <[e-mail]>; [e-mail]
Subject: Re: [Pce] draft-ietf-pce-pce-initiated-lsp

Hi Jon,

Thanks for your reply.
My interpretation of the following section of the existing draft-ietf-pce-pce-initiated-lsp is that PCC cannot just re-delegate PCE initiated LSP to a PCE.

<snip>

    In case of PCEP session failure, control over PCE-initiated LSPs
    reverts to the PCC at the expiration of the redelegation timeout.  At
    this point, the LSP is an "orphan" until the expiration of the State
    Timeout timer.  To obtain control of a PCE-initiated LSP, a PCE
    (either the original or one of its backups) sends a PCInitiate
    message, including just the SRP and LSP objects, and carrying the
    PLSP-ID of the LSP it wants to take control of.  Receipt of a
    PCInitiate message with a non-zero PLSP-ID normally results in the
    generation of a PCErr.  If the LSP is an orphan, the PCC MUST NOT
    generate an error and MUST redelegate the LSP to the PCE.  The State
    Timeout timer for the LSP is stopped upon the re-delegation.
</snip>

I read it as PCC is not free to delegate PCE initiated LSP even in orphan state, it rather waits (using State Timer) for other PCE server to "adopt" such "orphan" LSP.
This behavior is different for the PCE initiated LSPs vs PCC initiated LSPs.
Hence my suggestion was a mechanism that will help redundant PCE servers to discover PCE initiated LSPs that enter "orphan" state and trigger "adoption"
process which is different then the just re-delegation.

Thanks
Aaron


On 2017-01-05 11:25 AM, Jonathan Hardwick wrote:
> Hi Aaron
>
> Thanks for the comment.  There are no procedures defined that would allow a PCE to initiate a take-over of an LSP from a PCC.  Rather, the PCC must delegate the LSP to an appropriate PCE (if the LSP is initiated by a PCE then it must initially be delegated to that PCE).  The cases you mention would be resolved by the PCC making a local decision whether or not to re-delegate the LSP to an alternative PCE.
>
> So, I am not sure that the "orphan" flag would be useful to the PCE, at least not for the purpose that you describe.
>
> Best regards
> Jon
>
>
> -----Original Message-----
> From: Pce [mailto:[e-mail]] On Behalf Of Aaron Itskovich
> Sent: 04 January 2017 20:08
> To: [e-mail]
> Subject: Re: [Pce] draft-ietf-pce-pce-initiated-lsp
>
>
> I suggest to add indication that PCE Initiated LSP is orphan to LSP object in PCReport message. This information will be useful in facilitating takeover of an orphan LSP by redundant PCE server.
>
> Option 1) Adding bit to the LSP flags (L-bit "parentless/orphan") that will be set in the LSP object of the PCReport message sent when PCE Initiated LSP becomes orphan as result of connection loss to the PCE server that initiated this LSP or because such PCE server returns LSP delegation to the PCC to initiate transfer of LSP "ownership" to another PCE server.
>
> Option 2) Adding bit to the LSP flags (D2-bit ) that is set when such LSP is delegated to any PCE server. In this option PCE receiving report will be able to derive when PCE Initiated LSP is in orphan state when C flag in the report is set and the new D2-bit is not set.
>
>
> This proposal (regardless which option 1 or 2 is used ) alows PCC to propagate "orphan" state for the PCE initiated LSP to all PCE servers.
> It will help to trigger takeover of a PCE initiated LSP. The existing alternative is to rely on the PCE server to server communication for detection of such events which is prone to errors.
>
> For example:
>
>       - loss of communication between PCE-A and PCE-B may be interpreted as "takeover" trigger which is not necessarily true as PCE-A<->PCC connection may still be up.
>       - In case where PCE-A <-> PCC connection is down and both PCC 
> <-> PCE-B and  PCE-A <-> PCE-B connections are up we will need each 
> PCE server to distribute information about connection with it's 
> clients to all peers
>
> The suggestion frees PCE server from the need to propagate it's client connection status to all other PCE servers.
>
> Let me know what you think
>
> Thanks
> Aaron
>
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