The MPLS WG Archive

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

Eric Gray wrote:
> 
> Interesting.  Are you perhaps referring to 'reading you own
> messages' as snooping?  If you are, then the rest of what you say
> makes perfect sense.

Yes.  I'm talking about using incoming Path/Resv messages for a purpose
additional to simply creating Path/Resv state.

When you receive a Path or a Resv from a neighbor, and the TTL indicates
that there were no non-RSVP routers between you and the neighbor, you
can assume that the address in the HOP object is a directly-attached
RSVP-capable router.  It is therefore an address you may want to start
exchanging Hellos with.

Once the last amount of state goes away, however, you can no longer make
that assumption.

If you continue sending Hellos, you can still detect a failure, if you
stop getting acknowledgements, or if the neighbor's instance ID
changes.  If the ID changes, you can even continue sending Hellos, since
you know that the box is still there.  If the acknowledgements stop,
however, you don't know if the box is administratively down, rebooting,
crashed, or turned off.

And it serves no purpose (other than perhaps in a debugging effort) to
detect a neighbor failure when there is no established state, since
there's nothing to tear down.

-- David