Configuring Interfaces IP address for IGP and BGP ISP interface FastEthernet0/0 ip address 121.121.121.1 255.255.255.252 interface FastEthernet0/1 ip address 122.122.122.1 255.255.255.252 A1 interface Loopback1 ip address 100.100.100.1 255.255.255.255 interface FastEthernet0/0 ip address 192.168.100.1 255.255.255.0 interface FastEthernet0/1 ip address 121.121.121.2 255.255.255.252 A2 interface Loopback1 ip address 100.100.100.2 255.255.255.255 interface FastEthernet0/0 ip address 192.168.100.2 255.255.255.0 B1