To communicate with other devices, each machine evaluates the network portion of the IP address it desires to communicate with (the destination device) and the network portion of its IP address. If the two network values are the same, the machine attempts to communicate directly with the destination machine. If the network portions of the two IP addresses are different, then the local machine sends the packet to the default gateway.

The default gateway will then decide where the destination is by evaluating the network portion of the IP address and send it to the next device.

You configure a default gateway if the network contains routers (the default gateway is a router). A router is a device that connects two or more network segments (IP subnetworks) together.

Routers function at the Network layer of the OSI model. You can configure a Windows 7 computer or Windows Server 2008 to act as a router by installing two or more network cards in the server, attaching each network card to a different network segment, and then configuring each network card for the segment to which it will attach.

You do not send packets to the default gateway; the network protocol does by getting the physical address (MAC) or the default gateway and inserting it as the destination MAC address with the actual destination IP or the remote device.