The MPLS WG Archive

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

"Sanford, Bill" wrote:
> 
> There is a way for the ingress LER to know.  You need to implement ERO
> and RRO.  Either way, you will get the RESV message or you should get
> an error of a failed node.

Why?

This assumes that an entire switch (or interface) has failed, and has
been down long enough for its neighbors to detect the failure (perhaps
via routing table changes).

Consider, however, a router that is heavily loaded and is running low on
memory.  Carrier on the link remains up.  Routing protocols may continue
updating each other.  Even RSVP Hello messages may continue exchaning
OK.  But the low-memory may result in some degree of packet loss.  If an
RSVP path message is received, and dropped due to lack of memory, how is
the previous-hop router going to detect this and generate an error?

The answer is that it won't.  But it shouldn't matter, because the
normal soft-state mechanism will refresh the state, hopefully
successfully on the next try.

-- David