[c-nsp] benefit of uRFP with ACL over ACL on interface

[sthaug at nethelp.no]

> > In addition, certain common ACL entries (such as anti-spoofing
> > filters) don't fit very well into the general ACL structure and thus
> > require quite a bit of TCAM space.  Using uRPF might reduce TCAM usage
> > in such a case.  Of course, this is only relevant on very few
> > platforms.  You often can't use uRPF in strict mode because it can't
> > cope with the current BGP table size.
> 
> Why would one want to run uRPF in strict mode on an interface over 
> which you get a full BGP feed?  Or is the implementation so flawed 
> that it requires to conserve "double space" of all the routes on the 
> system, even if they weren't used on that particular interface?

I believe the Cisco 6500/7600 with Sup2/MSFC2/PFC2 works like that -
as soon as you turn on uRPF on one interface, your routing table is
programmed twice in the TCAM.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no