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

[Florian Weimer]

* LIM Fung:

> It all depends on what you want to achieve. uRPF when used in loose mode 
> allows for remotely triggered drops/filters in a short timeframe, which 
> is difficult to achieve with ACL.
>
> However, uRPF doesn't allow for filtering granularity (matching 
> protocol/ports) like what xACL allows.

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.