Is it time to abandon bogon prefix filters?

Jared Mauch jared at
Mon Aug 18 07:33:08 CDT 2008

On Sun, Aug 17, 2008 at 07:57:25PM -0500, Pete Templin wrote:
> Tomas L. Byrnes wrote:
>> Since there are ways to dynamically filter the bogons, using BGP or DNS,
>> I don't really see the need to stop doing so. If you're managing your
>> routing and firewall filters manually, you have bigger problems than the
>> release of Bogon space. 
> Can you share the Cisco configuration snippet you recommend to  
> dynamically FILTER bogons using BGP or DNS?

	On a router with full routes (ie: no default) the command

Router(config-if)#ip verify unicast source reachable-via any 

	Go ahead and try it out.  you can view the resulting
drop counter via the 'show ip int <x/y>' command.

	While you're at it, you also placed the reachable-via rx on
all your customer interfaces.  If you're paranoid, start with the 'any'
rpf and then move to the strict rpf.  The strict rpf also helps with
routing loops.

	- Jared

Jared Mauch  | pgp key available via finger from jared at
clue++;      |  My statements are only mine.

More information about the NANOG mailing list