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From: Eric Gray (eric.graySANDBURST.COM)
Date: Tue Apr 23 2002 - 09:32:56 CDT
Balaji R (Networking) - CTD, Chennai. wrote:
>From: wu min [mailto:made_in__chinaHOTMAIL.COM]
>Sent: Tuesday, April 23, 2002 6:05 AM
>Subject: Route Aggregation
>I have some questions and I hope someone out there can help.
>1) I understand that when a router tries to route a packet it must use the
>packet's destination address to search for the longest match prefix entry
>in it routing table to determine how and where the packet is supposed to be
>forwarded. Supposely the router break this rule and use a prefix which is
>not the longest match regardless of the existent of a longer one, what would
>be the consequences assuming that the next hop router for the chosen prefix
>is different from the longest match prefix? Is this safe?
> Not all the time. If the other router thinks that you are the next
>hop for the longer prefix, this will result in a routing loop.
I doubt that this is ever 'safe' - though you may get away with it.
In order to get away with it, other routers must not have a preferred route
such that the packet will subsequently arrive at the same router. The case
where the peer router thinks the local router is the next hop will not
result in a routing loop - it would be a black hole instead - because
horizon' behavior will prevent it from returning the packet to the router
from which it has received it. But there are a ton of other ways in which
the packet may end up arriving at the local router again, resulting in a
-- -- Eric Gray (mailto:eric.graysandburst.com) http://www.mindspring.com/~ewgray