so lets say you try to setup a PC on a LAN using a static IP address. but you dont put a default gateway in your configuration settings. well, you still be able to communicate with other computers in your LAN but not with other LANs or WANS - WANs like the internet. this is because the default gateway machine is a router that transfers data between two or more network segments. so if a computer is not configured to use a default gateway, it will not be able to communicate beyond the LAN.