[101680] in North American Network Operators' Group
RE: BGP Filtering
daemon@ATHENA.MIT.EDU (Jon Lewis)
Tue Jan 15 14:04:07 2008
Date: Tue, 15 Jan 2008 14:02:33 -0500 (EST)
From: Jon Lewis <jlewis@lewis.org>
To: Ben Butler <ben.butler@c2internet.net>
cc: nanog@merit.edu
In-Reply-To: <F9181128E9584B40B5A04C43800604B406DCDD@anyanka.c2internet.net>
Errors-To: owner-nanog@merit.edu
On Tue, 15 Jan 2008, Ben Butler wrote:
> I want a filter that will automatically match the shorter prefixes that
> match any longer prefix, once I can match them I can drop them.
> I don't want to manually configure a static prefix list for lots and
> lots and lots of reasons.
> If the longer prefix disappears from the route table I want to stop
> filtering the shorter prefixes - automatically.
This was talked about / requested several months ago on cisco-nsp. IIRC,
the thread ended along the lines of don't hold your breath.
Implementation of this sort of feature is very icky (lots of details you
may not be considering) and why should cisco spend time writing this code
when they can sell you a bigger router instead?
If the filter has to remember routes that are filtered so they can be
automatically unfiltered if their covering prefix is withdrawn, then
where's your savings? You can't have tea and no tea simultaneously. You
want to filter routes, but keep them around (and extra pointers connecting
their covering prefixes to them) in case they're needed in the
future...sort of like partial soft-reconfig. On a platform like the 6500
where you may have surplus RAM but limited TCAM, that could work...on the
software routers where RAM is the limiting factor it's not going to help.
--
----------------------------------------------------------------------
Jon Lewis | I route
Senior Network Engineer | therefore you are
Atlantic Net |
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________
