[c-nsp] Default route pointed to an interface

[Justin Shore]

This has been talked about before on this list but I'd like to bring it 
up again for my particular situation.

I have a pair of border routers, 1 with 2 upstream connection and the 
other with a single connection.  I'm pulling down full tables from each 
provider and have iBGP between the border routers and the core routers. 
  Each border router has a static default pointed to the outgoing 
interface for the local upstream connections (2 on one router and 1 on 
the other).  As expected the router with 2 default routes flops back and 
forth between the 2 interfaces every second or two.

35578126: Aug 16 10:20:22.385 CDT: RT: SET_LAST_RDB for 0.0.0.0/0
   OLD rdb: is directly connected, GigabitEthernet0/3
   NEW rdb: is directly connected, ATM1/0.1

35578127: Aug 16 10:20:23.645 CDT: RT: SET_LAST_RDB for 0.0.0.0/0
   OLD rdb: is directly connected, ATM1/0.1
   NEW rdb: is directly connected, GigabitEthernet0/3

I know that this forces an ARP query every time a packet falls back on 
the default route.  That isn't desirable of course.  However if I don't 
hardcode the default route each border router will learn the default 
from the other border router thanks to the IGP (both borders originate 
the default for the benefit of the rest of the network behind it).

Given that these routers have full tables the only time I can think of 
that a packet should not find its destination in the RIB is if it's for 
a route that I'm dampening or it's a bogon (which I'm catching with 
ingress/egress filters anyway).  However routing these packets to the 
other border router results in less than optimal routing.  I would like 
to implement uRPF on the upstream interfaces though so the default 
routes will have to be removed for that to work.

So a question would be how I remove the static default without learning 
the default from the IGP (distribute-list?)?  What would be the proper 
configuration for this scenario?  Besides the frequent ARPs and my uRPF 
desires, is this really a big problem?  Or am I missing something 
obvious again? :-)

Thanks
  Justin