RE: Permitting specific prefixes in BGP

From: Steven M. Sowell (ssowell@xxxxxxxx)
Date: Fri Feb 15 2002 - 11:39:05 GMT-3


   
It seems strange to me that you are getting this result. In my reading &
experimentation, if I have three networks, 10.1.200.0/25, 10.1.202.0/25, and
10.1.204.0/25, and wish to unsupress them all, I use the following(unrelated
config commands omitted):

router bgp 1100
 aggregate-address 10.1.192.0 255.255.224.0 summary-only
 neighbor ext unsuppress-map vlans
 neighbor 172.16.1.105 peer-group ext
!
ip prefix-list vlans seq 5 permit 10.1.200.0/21 ge 25 le 25

But if I use the prefix-list: "ip prefix-list vlans seq 5 permit
10.1.200.0/21"
it doesn't work. This, I believe, is because if you don't specify a prefix
length with the "le" or "ge" options, the /21 serves as both the match
criteria AND the prefix length, ie, 'exact match'. Either you misinterpreted
your results, or I am about to learn something about prefix-lists! The plot
thickens....
Steven Sowell
CCIE#7317

-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Asbjorn Hojmark
Sent: Thursday, February 14, 2002 7:47 PM
To: ccielab@groupstudy.com
Subject: Permitting specific prefixes in BGP

I have a router that I want to announce 10.0.0.0/8 as an aggre-
gate. This will suppress tons of other networks. But I also want
to unsuppress a couple of specific networks (e.g. 10.12.0.0/16)
to a specific peer.

I've tried using

 router bgp 1010
   aggr 10.0.0.0 255.0.0.0 summ
   neigh a.b.c.d unsupp NETS-LYNG

 route-map NETS-LYNG perm 10
   match ip addr ip pref NETS-LYNG

 route-map NETS-LYNG deny 20

 ip pref NETS-LYNG permit 10.12.0.0/16
 ip pref (etc).

But that doesn't seem to do the trick, as that also unsuppresses
10.12.1.0/24, which I still want to be suppressed.

Any ideas?

TIA,
-A

--
Heroes: Vint Cerf & Bob Kahn, Leonard Kleinrock, Robert Metcalfe
Links : http://www.hojmark.org/networking/


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