Networking 101: Understanding Subnets and CIDR Jul 31, 2008, 21 :00 UTC (0 Talkback[s]) (4519 reads) (Other stories by Charlie Schluting)
"An IP address consists of a host and a network portion. Coupled with a subnet mask, you can determine which part is the subnet, how large the network is, and where the network begins. Operating systems need to know this information in order to determine what IP addresses are on the local subnet and which addresses belong to the outside world and require a router to reach. Neighboring routers also need to know how large the subnet is, so they can send only applicable traffic that direction. Divisions between host and network portions of an address are completely determined by the subnet mask."
