[23652] in North American Network Operators' Group
Re: Cisco Route filtering [was Re: OPS: BGP spew from ASN 7374]
daemon@ATHENA.MIT.EDU (alex@nac.net)
Thu Apr 8 04:16:05 1999
Date: Thu, 8 Apr 1999 04:14:29 -0400 (EDT)
From: alex@nac.net
To: "R.P. Aditya" <aditya@dnai.com>
Cc: nanog@merit.edu, Sean Donelan <SEAN@SDG.DRA.COM>
In-Reply-To: <199904072141.OAA13178@mercury.dnai.com>
Errors-To: owner-nanog-outgoing@merit.edu
I've had a question on this for some time that maybe can get answered
here.
Let's assume for a moment that I have a network of 209.123/18 (1/4 of a
classful B).
Let's further assume that my upstream filters me with:
access-list 2002 permit ip host 209.123.0.0 host 255.255.0.0
neigh 2.3.4.5 distrib 2002 in
Will my /18 announcement make it through this /16 filter?
Would the same be true with a prefix-length filter, which I assume the
syntax would be:
ip prefix-list 1 permit 209.123.0.0/16
neigh 2.3.4.5 prefix-list 1 in
Thanks.
On Wed, 7 Apr 1999, R.P. Aditya wrote:
>
> This should probably be moved to cisco-nsp if it gets any more in-depth,
> however:
>
> > Cisco: could we please have more config memory, so we can load access-lists
> > for even huge BGP peers?
>
> Although you're probably asking for exactly what you say, config memory, it
> might also be useful to use prefix-lists to filter routing announcements:
>
> http://www.academ.com/nanog/june1998/turner/sld014.htm
>
> and the notes on bug CSCdk93005 seem to indicate that prefix-lists do make a
> difference and should be used over access-lists for filtering routes...
>
> Hope that helps,
> Adi
>
>
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
Atheism is a non-prophet organization. I route, therefore I am.
Alex Rubenstein, alex@nac.net, KC2BUO, ISP/C Charter Member
Father of the Network and Head Bottle-Washer
Net Access Corporation, 9 Mt. Pleasant Tpk., Denville, NJ 07834
Don't choose a spineless ISP; we have more backbone! http://www.nac.net
-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
