RE: BGP Filtering

["Mike Walter" <mwalter () 3z net>]

Ben,
Look here.  They show an example of prefix filtering on the 128.0.0.0/8
network.  I would assume you could extrapolate and come up with your own
rule.

http://www.cisco.com/en/US/docs/ios/12_0/np1/configuration/guide/1cbgp.h
tml#wp7487 


Mike Walter, MCP
Systems Administrator
3z.net a PCD Company
http://www.3z.net

-----Original Message-----
From: owner-nanog () merit edu [mailto:owner-nanog () merit edu] On Behalf Of
Ben Butler
Sent: Tuesday, January 15, 2008 11:45 AM
To: nanog () merit edu
Subject: RE: BGP Filtering


Hi Jason,

Fantastic news, it is possible.  We are using Cisco - would you be so
kind as to give me a clue into which bit of Cisco's website you would
like me to read as I have already read the bits I suspected might tell
me how to do this but have guessed wrong / the documentation hasn't
helped - so a handy pointer would be appreciated.

Kind Regards

Ben 

-----Original Message-----
From: Jason Dearborn [mailto:jasondearborn () gmail com] 
Sent: 15 January 2008 16:35
To: Ben Butler
Subject: Re: BGP Filtering

That's typically a function of your router software.  Juniper, Force10,
and Cisco all have support for this.  Check your manual.

On Jan 15, 2008 8:11 AM, Ben Butler <ben.butler () c2internet net> wrote:
> Hi,
>
> Considering:
>
> http://thyme.apnic.net
>
> Total number of prefixes smaller than registry allocations:
113220
> !!!!!
>
> /20:17046   /21:16106   /22:20178   /23:21229   /24:126450
>
> That is saying to me that a significant number of these smaller 
> prefixes are due to de-aggregation of PA and not PI announcements.
>
> My question is - how can I construct a filter / route map that will 
> filter out any more specific prefixes where a less specific one exists

> in the BGP table.
>
> If my above conclusion is correct a significant portion ~47% of the 
> number of the prefixes in the table could be argued to be very 
> unnecessary at one level or another.
>
> Is such a filter possible easily or would it have to be explicitly 
> declared, any chance of a process the automatically tracks and 
> publishes a list of offending specifics similar to Team Cymru's Bogon
BGP feed.
> As a transit consumer - why would I want to carry all this cr*p in my 
> routing table, I would still be getting a BGP route to the larger 
> prefix anyway - let my transit feeds sort out which route they use & 
> traffic engineering.
>
> Thoughts anyone?
>
>
> Kind Regards
>
> Ben