[nsp] bgp - aggregates and specific routes

[Roger]

I have a question reguarding BGP aggregate routes and more specific 
routes. Currently we have 2 WAN links w/ large carriers running eBGP, we 
advertise our /19 aggregate, example 192.168.0.0/19.

A customer of ours, who's range is say 192.168.16.0/24 will be using our 
numbers and advertising said route to other eBGP peers.

My question is - if the link between us and our customer at 16.0/24 goes 
down we need to advertise that 16.0/24 as invalid while still 
advertising our /19. The customer w/ the 16.0/24 should still be 
connected via their other eBGP links.

How would I do this? Currently my BGP setup is like so. Now if the 
16.0/24 peering session goes down traffic will still flow because it 
will be lumped into our /19.


router bgp 1
no synchronization
bgp log-neighbor-changes
network 192.168.0.0 mask 255.255.224.0
neighbor 1.2.3.4 remote-as 1234
neighbor 1.2.3.4 description WAN Link 1
neighbor 1.2.3.4 send-community
neighbor 5.6.7.8 remote-as 5678
neighbor 5.6.7.8 description WAN Link 2
neighbor 5.6.7.8 send-community
neighbor 192.168.16.254 remote-as 2
neighbor 192.168.16.254 description downstream customer
neighbor 192.168.16.254 send-community
!
ip route 192.168.0.0 255.255.224.0 Null0