From: Willy Schoots (w.schoots@chello.nl)
Date: Sun Feb 01 2004 - 11:55:48 GMT-3
An easy filter for this situation is ^$ | \)$
^$ = routes originated in the subAS of the router where you apply the
filter
\)$ = routes originated in any other subAS
Cheers,
Willy Schoots
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Bob Sinclair
Sent: zaterdag 31 januari 2004 23:16
To: Hossam; ccielab@groupstudy.com
Subject: Re: AS-Path Filtering with BGP Confiderations!
Sam,
I can confirm that your AS 200 will not show up within the sub-ASs. So
if
you do sho ip b reg ^$ you will see routes from the local sub-as, not
routes
from AS 200.
To do an as-path filter that will send only routes from within AS 200,
you
would have to include the empty path, ^$, as well as all other sub-ASs.
This is quite inconvenient! For just this reason, perhaps it would be
desirable in a real-world implementation to keep your AS border routers
out
of your confederations. That way you can easily permit ^$ to allow only
your own routes outbound.
HTH,
Bob Sinclair
CCIE #10427, CISSP, MCSE
www.netmasterclass.net
----- Original Message -----
From: "Hossam" <sam6626@yahoo.com>
To: <ccielab@groupstudy.com>
Sent: Saturday, January 31, 2004 5:41 AM
Subject: AS-Path Filtering with BGP Confiderations!
> I am trying to configure a BGP router R2 in (AS 65 256 and Bgp
Confideration indentifier 200) to limit it advertesment to its EBGP
neighbour (R4 in AS 300) to the routes that was originated in AS 200.
>
> I noticed that while i am AS-path filtering (either via filter-list or
a
route map) and an ip as-path accesslist that permits only ^200$,
nothing
gets advertised to the neighbour R4.
>
> Once i remove the as-path filtering i get the routes with AS-path =
200 at
R4 as expected.
>
> I think the problem is that R2 has the routes with AS-path = (65078)
cause
of the confidertaions in its BGP table.
> It seems that the IOS does the filtering first and then it strips of
the
confiderations as-path just before advertesting the routes to EBGP
neighbour.
>
> Now the question is: what is the best way to do the filtering in this
case? i hate the idea of filtering on the SUB ASs...any ideas...
>
> Thanks..
> SAM
>
>
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This archive was generated by hypermail 2.1.4 : Fri Mar 05 2004 - 07:13:44 GMT-3