Folks, may be of interest for those having BGP3 and BGP4 peers. Arnold Arnold Nipper wrote:
Subject: Re: Specfic Routes AS 1324 To: jyy@merit.edu (Jessica Yu) Date: Fri, 20 May 1994 01:39:02 +0200 (MET DST) Cc: nipper@xlink.net, as1324@merit.edu, gsp@merit.edu, nsfnet-admin@merit.edu, sjr@merit.edu In-Reply-To: <199405191444.KAA14728@merit.edu> from "Jessica Yu" at May 19, 94 10:44:42 am Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Content-Length: 1869 From: Arnold Nipper <nipper@xlink.net> Sender: nipper@xlink.net Message-Id: <"xlink100.x.634:19.04.94.23.39.06"@xlink.net>
Jessica Yu wrote:
Arnold,
Steve's suggestion is a good one. If you can not get answer from there, you can also try bgpd@merit.edu.
We see other cases like this. When you figure out what's going, please let us know.
Jessica,
there is an example in the latest BGP4 notes
ftp.cisco.com:ftp/bgp_beta/BGP4_notes
which should solve the problem. I'll try it tomorrow morning.
We can pass it to others. Thanks!
--Jessica
-- Arnold
------------------------------------------------------------------------------ Route Filtering in a CIDR world
In current 9.21 software, access lists may be used as a mechanism to filter routing updates (either going to a particular neighbor or between routing protocols). Unfortunately, with the existing mechanism, there is no way to distinguish between 131.108.0.0 255.255.0.0 and 131.108.0.0 255.255.255.0, which poses a problem to CIDR users wishing to do advanced filtering of networks and masks.
In order to cope with this situation, we've hacked on the semantics for extended access lists so that you can use them to filter both networks and masks. (Yes, we think this is a kludge too.)
the syntax is:
access-list <list> [permit|deny] ip <net> <net-wildcard> <netmask> <netmask-wildcard>
Example: permit 192.108.0.0 255.255.0.0 but deny any more specific routes of 192.108.0.0 (including 192.108.0.0 255.255.255.0).
access-list 101 permit ip 192.108.0.0 0.0.0.0 255.255.0.0 0.0.0.0 access-list 101 deny ip 192.108.0.0 0.0.255.255 255.255.0.0 0.0.255.255
Example: permit 131.108.0/24 but deny 131.108/16 and all other subnets of 131.108.0.0
access-list 101 permit ip 131.108.0.0 0.0.0.0 255.255.255.0 0.0.0.0 accces-list 101 deny ip 131.108.0.0 0.0.255.255 255.255.0.0 0.0.255.255
------------------------------------------------------------------------------
-- Arnold Nipper / email: nipper@xlink.net NTG Netzwerk und Telematic GmbH \/ phone: +49 721 9652 0 Geschaeftsbereich XLINK /\ LINK fax: +49 721 9652 210 Vincenz-Priessnitz-Str. 3 /_______ D-76131 Karlsruhe, Germany