[c-nsp] BGP questions

[Troy Davis]

Have each 6500 originate the routes they can reach.

For a route to be announced via a BGP network statement, the same route must
exist in the routing table.  I suspect the 7x00s have BGP network
statements for the routes as well as "tie-down" routes (usually to the
null0 interface) for them.

Move the null0 routes to the 6500s so the border routers learn them via
OSPF or another IGP.  Should the border routers split, they'll only
announce routes they can reach.

Each 6500 and its downstreams need to use a large enough subnet to meet
prefix length filters (generally /24 these days).  For example, /28s from
the same class C can't be in use on different 6500s.

One ugly option to handle that scenario: a tunnel over your two Internet
connections, carrying an IGP session with a high IGP cost.  You'll be
triple-billed for the traffic - in, out, in - so you'd still want to
minimize the subnets used by both 6500s.  Not to mention the CPU hit for
encryption; cleartext may be an option, recognizing the risks.

I'd still create a full IBGP mesh in the meantime for design completeness.
It wasn't meant to be partially meshed without route reflectors, though
the default routes take care of reachability.

Troy