From: Hansang Bae (hbae@xxxxxxxxxx)
Date: Sun Apr 21 2002 - 00:53:50 GMT-3
At 10:35 AM 4/20/2002 -0400, Howard C. Berkowitz wrote:
[snip]
>The reason that OSPF always prefers intra-area to inter-area, inter-area to ex
ternal*, is preventing loops from something similar to incorrect redistribution
. Think of it as a matter of trust.
>All the routers in an area have the same database and KNOW that a route is loo
p-free. Since inter-area routes started out in an area that followed this rule
and passed in a controlled way through the backbone, they are almost as truste
d...but less so, because some weird backbone error conceivably could have cause
d a route generated in the local area to go into the backbone and get readverti
sed back into the local area. Externals can't really be trusted at all. After
all, they could have resulted from the local system redistributing into another
routing protocol at ASBR1, and the local system relearning them at ASBR2.
[snip]
Actually, Doyle covers this (in a round-about way). As he put it, At the ABRs,
OSPF does act like distance vector protocols. That is, they have to trust wha
t the other areas say is true.
hsb
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