Subject: RE: Simple question

From: Michel Gilbert <[email-masked]>
Date: Wed, 13 Feb 2002 11:37:43 -0500

Ali -

Vernon's comments in his previous response were essentially correct and I
was imprecise. If the failure of R4 takes down the link between R3 and R4 -
the failure of the link will be immediately detected at R3 by virtually
every protocol (except static routing) and propagate quickly. If the link is
something like a shared Ethernet, then older routing protocols (e.g., 
) may take some time to recover because they lack a "heartbeat" mechanism,
and can only detect the failure by the absence of periodic updates from the
neighbor.

So the answer, as always, is "it depends" :)

/Michel

-----Original Message-----
From: Ali Boudani [mailto:[email-masked]]
Sent: Wednesday, February 13, 2002 6:49 AM
To: [email-masked]
Subject: Simple question

If we have the following figure:

R1---------R2---------R3---------R4 where R1 to R4 are unicast routers.
R1 is sending packets to R4. If R4 goes down, when R1 will detect this??
Before sending packets or after?