Windows Server 2008 and Routing

When IP networks become large, they are typically segmented into subnets to keep local data traffic on each segment and to make the most out of available network bandwidth. Networks that are made up of multiple sites (geographic locations) also use subnets to divide the various parts of the network into one internetwork (a network of networks).

The device that joins separate segments (subnets in the case of a TCP/IP network) into one network is called a router. A router is an intelligent networking device that can determine whether data should stay on the local segment (subnet) or be forwarded to another subnet on the network.