[nsp] BGP, best way to balance outgoging traffic

[Lukas Krattiger]

Greetings,

We are currently running our BGP with 4 upstreams and anounceing 6 prefixes.
The advertisement of this 4 prefixes over upstream a + b and 2 prefixes 
over upstream c + d are working fine.
What's now the best way to tell the outgoing traffic from all of this 2 
prefixes must take upstream c + d and the other 4 prefixes are only allowed 
to use upstream a + b ?
Any examples ?

Best Regards
-Lukas