Stephane,
Lots of thanks for a prompt and very important (to me) response.
Indeed the main use case of interest for my colleagues and myself is the PCC
restart that should be non-traffic affecting if control plane (including the
PCC) and forwarding plane have independent life spans.
The critical question here is, whether this can be achieved by purely local
policies (within the restarting node) or requires some protocol adjustments.
Regards,
Sasha
Office: +972-39266302
Cell: +972-549266302
Email: [email protected]
From: [email protected] [mailto:[email protected]]
Sent: Thursday, June 22, 2017 11:14 AM
To: Alexander Vainshtein <[email protected]>; [email protected]
Cc: Michael Gorokhovsky <[email protected]>; [email protected];
[email protected]; Marina Fizgeer <[email protected]>; Alexander Ferdman
<[email protected]>
Subject: RE: [Pce] Is there any activity related to PCE graceful restart?
Hi Sasha,
As Dhruv mentioned, restarting a PCE is not a big deal, we have already the
mechanism defined to handle this without traffic disruption.
Your email mentions also, PCC control plane restart which is a bit more tricky
IMO.
>From a PCC point of view, I think you request the PCC to keep the dataplane
>intact when the PCC process or RSVP process or IS-IS is getting down (during
>failure or restart or upgrade...). For the PCC process, I think this could be
>addressed by a purely local mechanism.
Now I see a case where the PCE needs to keep the state from a PCC when the PCC
restarts => my favorite disjointness use case or any other use case where LSPs
on other PCCs depends on the LSP of the PCC which is restarting.
Let's say that PCC1 owns LSP1, PCC2 owns LSP2.
LSP1 and LSP2 depends of each other.
If the PCE loses the state of LSP1 because PCC1 restarts, it may reroute LSP2
on a path that does not fulfill the dependency of the two LSPs anymore while at
the same time LSP1 was kept intact by PCC1 from a forwarding plane point of
view.
Is it a critical issue ? During a transient period (the PCC restart), some LSPs
may not fulfil their constraint anymore. Does it justify extensions to the
protocol ?
I do not have a strong opinion on that: it's always a question of complexity to
introduce vs gain.
Adrian, Dhruv, did I miss something ? Am I wrong ?
Brgds,
Stephane
From: Pce [mailto:[email protected]] On Behalf Of Alexander Vainshtein
Sent: Monday, June 19, 2017 14:48
To: [email protected]<mailto:[email protected]>
Cc: Michael Gorokhovsky; [email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>; Marina Fizgeer; Alexander Ferdman
Subject: Re: [Pce] Is there any activity related to PCE graceful restart?
Adrian,
Lots of thanks for a prompt response.
However, our primary interest is the control plane (including PCC) restart in a
network element with separated control and forwarding planes.
Specifically, my colleagues and I try to understand, how to make such a restart
non-traffic affecting while:
- The network uses Segment Routing for setting up paths computed by
the PCE. This means that these paths are only known to their respective
head-end nodes. This situation is different from the scenario where RSVP-TE is
used to signal these paths, since they cannot be re-learned from the neighbors
as part of the RSVP-TE graceful restart procedures
- The protocols used for distributing SR-related information (i.e.,
IGP and BGP SR extensions) are GR-capable, and GR for them is enabled in the
network
- The PCE is an active stateful PCE, i.e., it instructs the head-end
node, which paths should be set up without any requests coming from the nodes.
Hopefully this clarifies the context for our question.
It may well be that the requirement for non-traffic affecting control plane
restart can be addressed without any changed to the existing protocols.
Alternatively, it is possible that some minor changes (like making the PCE
aware of separation between the control and forwarding planes, negotiation of
GR capabilities and grace periods etc.) are required.
Any inputs would be highly appreciated.
Regards, and lots fo thanks in advance,
Sasha
Office: +972-39266302
Cell: +972-549266302
Email:
[email protected]<mailto:[email protected]>
From: Adrian Farrel [mailto:[email protected]]
Sent: Sunday, June 18, 2017 8:34 PM
To: Alexander Vainshtein
<[email protected]<mailto:[email protected]>>;
[email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>
Cc: Marina Fizgeer
<[email protected]<mailto:[email protected]>>; Michael
Gorokhovsky
<[email protected]<mailto:[email protected]>>;
[email protected]<mailto:[email protected]>; Alexander Ferdman
<[email protected]<mailto:[email protected]>>
Subject: RE: [Pce] Is there any activity related to PCE graceful restart?
Sasha,
What are you hoping to achieve?
That a restarting PCE can retain its TED and LSP-DB?
That a restarting PCE can synch state with the network?
That a restarting PCE with outstanding (unanswered) messages in either
direction can not need to resend them?
That a restarting PCE can resend outstanding (unanswered) messages without
problems caused by duplication?
I think you may want to read around the definition of the request-id. Although
5440 doesn't make it explicit, a lot comes from how you process the request-id.
That "a lot" arose from consideration of parallel sessions and distilled to not
needing to write about restart.
Cheers,
Adrian (resurrecting old memories, possibly not entirely accurately)
From: Pce [mailto:[email protected]] On Behalf Of Alexander Vainshtein
Sent: 18 June 2017 16:43
To: [email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>
Cc: Marina Fizgeer; Michael Gorokhovsky; [email protected]<mailto:[email protected]>;
Alexander Ferdman
Subject: Re: [Pce] Is there any activity related to PCE graceful restart?
Re-sending with the correct WG mailing list address...
Regards,
Sasha
Office: +972-39266302
Cell: +972-549266302
Email:
[email protected]<mailto:[email protected]>
From: Alexander Vainshtein
Sent: Sunday, June 18, 2017 6:41 PM
To: '[email protected]'
<[email protected]<mailto:[email protected]>>;
'[email protected]' <[email protected]<mailto:[email protected]>>;
'[email protected]'
<[email protected]<mailto:[email protected]>>
Cc: '[email protected]' <[email protected]<mailto:[email protected]>>; Michael Gorokhovsky
<[email protected]<mailto:[email protected]>>;
Marina Fizgeer <[email protected]<mailto:[email protected]>>;
Alexander Ferdman
<[email protected]<mailto:[email protected]>>
Subject: Is there any activity related to PCE graceful restart?
Hi all,
My colleagues and I tried to find any work in the PCE WG related to PCEP
graceful restart.
So far, we did not succeed. This could mean one of the following:
- Our search did not go deep enough. In this case pointers to any
specific documents would be highly appreciated
- Such work does not exist because (for some reason) it is not
required. This looks problematic to me, especially if we deal with a stateful
active PCE and the path computed by the PCE was implemented using Segment
Routing (so that only the head end of the computed path is aware of the path).
However, I could have missed something obvious, and any clarifications would be
highly appreciated
- Such work is required but, so far, nobody has taken care of it. The
implications are obvious:-(.
Your feedback would be highly appreciated.
Regards, and lots of thanks in advance,
Sasha
Office: +972-39266302
Cell: +972-549266302
Email:
[email protected]<mailto:[email protected]>
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