The MPLS WG Archive

["Feng, Mark" <m_feng@trillium.com>]

> -----Original Message-----
> From: David Charlap [mailto:David.Charlap@marconi.com]
> Sent: Tuesday, November 13, 2001 3:07 PM
> To: 'mpls@uu.net'
> Subject: Re: Hello Extension - destination IP address
> 
> 
> "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.
>

Right.
 
> > 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.
>

I agree. It makes more sense to start/re-start the Hello when we receive
messages (again) from the neighbour.
 
> -- David
>