The MPLS WG Archive

[David Charlap <David.Charlap@marconi.com>]

"Feng, Mark" wrote:
>>
>> Suppose the state goes away due to a link failure (lost carrier on
>> the fiber).  When the link comes back up, there may be a different
>> switch at the other end of the fiber.  If so, that switch may not
>> be running RSVP, or it may not support Hello, or it may simply
>> have a different IP address.
> 
> Wouldn't the Hello exchange timed out before the normal cleanup
> timer expiry?

Probably.  But if carrier is lost on the fiber, that will likely be
detected in hardware before the Hello times out.

> In either case, wouldn't the Hello state machine itself eventually
> settle to the correct state in the above cases?

Yes, it will successfully tear everything.  But do you want to restart
Hellos immediately or wait for new Path state?

IMO, if a neighbor address is configured, it makes sense to restart
Hellos immediately after tearing down local state, so you can know when
the neighbor comes back up (when you start getting Hello Acks back). 
But it would be foolish to do this if you're auto-discovering your
neighbor, because that neighbor might have disappeared from the network
altogether.

-- David