IP Network Addressing

Each computer or device (also called a host or node) in a TCP/IP network is uniquely identified by an IP address, consisting of a network ID and a host ID. Hosts with the same network ID belong to the same subnet and may communicate with one another without having to pass through a router. If the two network IDs are different, then the hosts must communicate through a router or network gateway.

Address Class

The class of an address determines which part of the IP address is the network ID and which part the host ID. The class may be determined by the decimal value of the first address byte.