BGP CONDITIONAL Advertisements - Advertise Maps

This is a pretty complex BGP issue because you really need to know the BGP philosophy and maybe even have some basic experience in programming. The trick is to change the behaviour of the BGP advertisements depending on the routes that are being learned.

Step 1:
Configure 2 Route Maps, one for the CHECK condition, and another for PREFIXES you will advertise if CHECK passes.
For example we want to CHECK if the 2.0.0.0 is learned:
(config)#access-list 2 permit 2.0.0.0
(config)#route-map CHECK permit 10
(config-rmap)#match ip address 2

And ONLY if it's NOT in the routing table, we want to advertise 1.0.0.0
(config)#access-list 1 permit 1.0.0.0
(config)#route-map ADVERTISE permit 10
(config-rmap)#match ip address 1

Step 2:
Configure the advertise map and the condition in the BGP routing process:
(config)#router bgp 65545
(config-router)#neighbor 10.1.12.2 advertise-map ADVERTISE ?
  exist-map      advertise prefix only if prefix is in the condition exists <- CHECK THESE OPTIONS
  non-exist-map  advertise prefix only if prefix in the condition does not exist
(config-router)#neighbor 10.1.12.2 advertise-map ADVERTISE non-exist-map CHECK

Intuitively we can see that the ADV_ROUTE_MAP is the route map that defines the routes that will be broadcast, in this case if the conditions defined in the route-map CONDITION_ROUTE_MAP is NOT satisfied, meaning - if the prefixes are NOT in the table.