BGP related

Fri Jul 10 21:01:44 UTC 1992

Hi,

For those sites who BGP peer with both T1 NSS and T3 ENSS, please note
the following:

By default, cisco will advertise all the routes learn from one neighbor
to the other neighbor(s).  For example, we have seen a lot of cases,
that the cisco advertise whatever it learns from T3 back to T1 and
vise versa.  That is a lot of overhead and should be avoided.

How?

cisco's lastest software 9.0 (tli130?) and above does provide a means
of building a firewall to prevent the advertisement.  Below is a 
sample config from Eric Sherk of SuraNet (Thanks Eric) which shows the
syntaxt for filtering.  This syntax is also useful for other inbound and
outbound filtering based on AS for each neighbor.  Have fun!

						--Jessica
Date: Fri, 10 Jul 92 15:52:45 -0400
From: Erik Sherk <sherk>

router bgp 86
default-metric 1
network 128.167.0.0
network 192.80.214.0
distance bgp 105 200 200
redistribute rip
neighbor 192.80.214.247 remote-as 145
neighbor 192.80.214.247 filter-list 94 out
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
neighbor 192.80.214.248 remote-as 690
neighbor 192.80.214.248 filter-list 93 out
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!
ip default-network 129.140.0.0
ip default-network 140.222.0.0
!

ip as-path access-list 93 deny 145 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ip as-path access-list 93 permit .*
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ip as-path access-list 94 deny 690
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ip as-path access-list 94 permit .*
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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