nanog mailing list archives
RE: BGP Filtering
From: Jon Lewis <jlewis () lewis org>
Date: Tue, 15 Jan 2008 14:02:33 -0500 (EST)
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the filter has to remember routes that are filtered so they can be automatically unfiltered if their covering prefix is withdrawn, then where's your savings?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_________
Current thread:
- Re: BGP Filtering, (continued)
- Re: BGP Filtering Dave Israel (Jan 15)
- RE: BGP Filtering Ben Butler (Jan 15)
- Re: BGP Filtering Dave Israel (Jan 15)
- Re: BGP Filtering William Herrin (Jan 15)
- Re: BGP Filtering Dave Israel (Jan 15)
- Re: BGP Filtering Deepak Jain (Jan 15)
- RE: BGP Filtering Ben Butler (Jan 15)
- RE: BGP Filtering Ben Butler (Jan 15)
- RE: BGP Filtering Mike Walter (Jan 15)
- RE: BGP Filtering Ben Butler (Jan 15)
- RE: BGP Filtering Jon Lewis (Jan 15)
- Re: BGP Filtering Christopher Morrow (Jan 15)
- Re: BGP Filtering Jon Lewis (Jan 15)
- Network Operator Groups Outside the US Rod Beck (Jan 16)
- Re: Network Operator Groups Outside the US Suresh Ramasubramanian (Jan 16)
- Re: Network Operator Groups Outside the US Fredy Kuenzler (Jan 16)