Subject: [pim] PIM graceful restart (non-stop forwarding) capability

From: "Srikanth Rao" <[email-masked]>
Date: Tue, 21 Aug 2007 14:00:56 -0700

Hi,

How do PIM routers know about the graceful-restart capability of their
peers? In BGP, OSPF and other protocols, this capability is advertised
upfront when the adjacencies are formed. So that when their neighbor
liveliness is lost, they hold on to the routes to support the non stop
forwarding of traffic. 

In PIM, a new GenID in the Hello message indicates that the router
restarted. But that doesn't necessarily mean that router is capable of
doing non stop forwarding. So, in other words, when a PIM speaker
detects that its neighbor has gone down (or restarting), what is the
criterion on which it holds on to the updates from its neighbor in
non-stop forwarding mode? Is there any standardized option or mechanism
for this? If this has been already discussed, can someone point me to
the discussion?

Thanks

Srikanth

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From: "janardhan kulkarni" <[email-masked]>
Date: Wed, 22 Aug 2007 12:42:37 +0530

Yes, as of now if does not have GR mechanism. The genid feature does
enable us to recreate the "most" of state machine quickly, it does not
gives rules for NON_STOP forwarding.

Also, GENID itself does not ensure proper rebuilding of the
state-machine completely.
It also does not ensure NLT does not expire , Joins do get timed out
(although it is rare) and it does not take into account the assert
state machine.

I had raised this concern some time back, and I think there is a need
to analyse this issue.

Thanks.

On 8/22/07, Srikanth Rao <[email-masked]> wrote:
> restarted. But that doesn't necessarily mean that router is capable of doing
> non stop forwarding. So, in other words, when a PIM speaker detects that its
> neighbor has gone down (or restarting), what is the criterion on which it
> holds on to the updates from its neighbor in non-stop forwarding mode? Is
> there any standardized option or mechanism for this? If this has been
> already discussed, can someone point me to the discussion?
>
>
>
> Thanks
>
> Srikanth
>
>
>
>

-- 
Bye,
Janardhan.
"I have never been hurt by what I have not said."
  -Calvin Coolidge