interface Loopback0
 ip address 3.3.3.3 255.255.255.0

interface Ethernet0/1
 ip address 192.168.23.3 255.255.255.0

router ospf 1
 network 3.3.3.0 0.0.0.255 area 0
 network 192.168.23.0 0.0.0.255 area 0