Router(config-router)#network 172.16.10.1 0.0.0.0 area 0
Read this line to say: Any interface with an exact address of 172.16.10.1 is to be put into Area 0
Router(config-router)#network 172.16.10.0 0.0.255.255 area 0
Read this line to say: Any interface with an address of 172.16.x.x is to be put into Area 0
Router(config-router)#network 0.0.0.0 255.255.255.255 area 0
Read this line to say: Any interface with any address is to be put into Area 0
