[c-nsp] Filtering /24s

[Joe Provo]

On Wed, Mar 15, 2006 at 07:29:39PM -0500, Greg Boehnlein wrote:
> Hello,
> 	We are looking at some strategies to reduce the load on our core 
> routers by filtering all routes that are /24 or smaller. The number of /24 
> routes that have propogated in the recent couple of years seems enormous 
> to me, and we are starting to hit the limits of the RSP-2 cards in our 
> 7500s. 

Yes, the folks who wish to have you pay for their traffic engineering
have won. CIDR is not just dead, but the zombie has gone to shambling
about and tearing apart perfectly sane pre-CIDR aggregates.  Often
this is done in the name of "security".

> Short of chucking the Cisco gear and replacing w/ something that 
> can handle a larger table, it seems reasonable to me that we could 
> probably reduce the total number of routes significantly if we just 
> dropped all the /24s on the floor and let our upstreams handle the routing 
> for us.

A sane place to apply some backpressure is where there should be
covering larger aggregates.  If someone shoots of their own connectivity
due to "traffic engineering" then whose problem is that? If they are
already deaggregating a single prefix into N, N+1 to include the 
larger aggregate shouldn't trouble them.  

--
Joe Provo                                            Voice  617.670.2904
Senior Manager, Internet Planning & Design           Fax    617.670.2920
Network Engineering, RCN                             <joe.provo at rcn.com>