From: Khalid Siddiq (khalid@sys.net.pk)
Date: Wed Sep 25 2002 - 03:22:34 GMT-3
Nick,
the requirement is, R5 advertise only an aggregate address to R4, but not to R2.
i belive that we have to filter the aggregate route on R2 also.
please calirfy if i am wrong
regards
khalid
-----Original Message-----
From: Nick Shah [mailto:nshah@connect.com.au]
Sent: Wednesday, September 25, 2002 6:21 AM
To: Young K. Bae; ccielab@groupstudy.com
Subject: Re: Need a verification on a BGP solution
Young,
comments inline...
> R5 has two EBGP peers - R2 and R4. R5 has five routes in its BGP table -
> 192.168.112.0, 192.168.113.0, 192.168.114.0, 192.168.115.0, and
> 172.109.109.0. All of these are /24 routes. The first objective is for
R5
> to not advertise 172.109.109.0 to both R2 and R4. The second objective is
> for R5 to advertise only an aggregate address to R4, but not to R2, while
> not advertising 192.168.112.0/24 to R2.
>
> The exact instruction from the IPExpert Lab#31 reads:
>
> "R5 should not advertise 172.109.109.0 to R2 or R4. R5 should advertise a
> single route for the Class C networks to R4. R2 should not have
> 192.168.112.0 in its BGP or routing tables. Do not use an access-list."
First you must construct aggregate address (without the summary only
option). Then construct a prefix list for denying 172.109.109.0 &
192.168.112.0 & permitting everything else. Construct another prefix list
for denying 172.109 & also denying 192.168.all/24 & permitting everything
else or permit the /16 only (either way this will only permit the /16)
Apply each of these to the respective neighbors.
You could acheive similar results with Route-maps, and distribute lists &
prefix lists out (there are a couple more 'screwy' ways apart from these as
well)If you are using distribute lists use prefix lists with it , instead of
access lists so as not to violate the conditions of the requirement.
Your solution is also correct.
rgds
Nick
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