You have to be in the same IP range to connect.Let me explain.if you have your ip address as 172.18.10.10 and subnet mask as 255.255.0.0 , then you can connect to people with addresses 172.18.xxx.xxx.If you keep mask as 255.0.0.0 you can connect with people with 172.xxx.xxx.xxx .So keep your mask as 255.0.0.0 (AFAIK you cant keep 0.0.0.0) , you will get maximum connectivity.