http://www.cisco.com/warp/public/104/3.html
sean@ertw.com

For EIGRP
------------
> Are they any way to remove the summary route pointing to the null0 interface ?
> With OSPF, it's possible to use the no discard-route ....
> With EIGRP ?

Hi,
try following command with admin-distance=255.
ip summary-address eigrp as-number network-address subnet-mask [admin-distance]

Regards
Erling Bjontegard

For BGP:

Aidan Marks <amarks@cisco.com> says:

distance 255 <source ip> <mask> <acl>

"Joe Chang" <changjoe@earthlink.net> chimes in with a caveat:

Looks like you want to advertise the aggregate address, but do not want to
keep it in the routing table. I don't think that's an option because the
route to Null0 is automatically installed as a routing loop prevention
feature. Say you had also had a default route pointing out to one of the AS
400 neighbors. If  your router received a packet from AS 400 for
"192.168.0.1" it would send it back to AS 400, which would send it back to
you, etc etc.

"Donny MATEO" <donny.mateo@sg.ca-indosuez.com> adds:

you need a new BGP protocol!

If you're worried about the so called no null0 route requirement in the exam, I suppose if they said
explicitly that you need to aggregate certain route they would have given you a clue if they don't
want you to use aggregate address (static and redistribute or network command ). Personally i take
it as if they want me to do something specific it will overwrite the other general rule.
It's like when they say, put a static route on this router and advertised it through bgp. If you
follow the general rule there should not be any static route bla bla bla unless specified otherwise.
If you're not sure and you have time, check it out with the proctor.