From: Howard C. Berkowitz (hcb@xxxxxxxxxxxx)
Date: Mon May 27 2002 - 16:51:04 GMT-3
At 8:30 PM -0700 5/25/02, Paul wrote:
>Hi guy,
>Here it is scenario. R1 is getting external routes
>from other AS. R1 is doing aggregation and sending
>only aggregate towards internal peers. Question is how
>to prevent R1 from installing specific routes into its
>own routing table.It should have only aggregate.
>Paul
>
There are several ways for me to interpret this, depending also if
it's a real-world or lab scenario.
First, I have to be absolutely clear what can be in the BGP table as
opposed to the main routing table.
Second, do I understand correctly that R1 is doing proxy aggregation
for other AS, not just aggregating some of its own routes?
Third, as would be characteristic of the real world, do you know the
aggregate address beforehand, or are you asking the router to
magically know what is an aggregate of which?
In general, this sounds like a prefix-list problem if I can't
constrain the external AS (which I might very be able to in the real
world), and they don't support outbound route filtering (a new
feature).
If, for example, AS999 advertised to you:
10.10.192.0/20
10.10.192.0/22
10.10.218.0/22
10.10.224.0/22
10.10.240.0/22
wouldn't an inbound prefix list such as
ip prefix-list abc deny 10.10.192.0/20 ge 21
do what you want?
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