ali,
confederation is used to reduce the number of IBGP session per router... its recommended to use route reflector or confederation when you have number of IBGP session is more than 100 per router.
so finally route reflector and the confederation is used to reduce the number of IBGP session...
when you are going to communicate with the internet then it will allow only to use the public IP address as well as the Public AS... so when you have private ip address then you are using the NAT and when you are using the private ip adddress then you are using remove private-as when communication with the global internet.
regards
Devang
