Class A – The first byte (8 bits) is the network component and the remaining three bytes (24 bits) are host component (network.host.host.host). This class is for an internetwork with small number of networks and large number of hosts per network.
Class B – The first two bytes (16 bits) are the network component and the remaining three bytes are host components (network.network.host.host). This class bridges the gap between Class A and Class C by providing for medium number of networks with medium number of hosts.
Class C – The first three bytes (24 bits) are the network component and the last byte (8 bits) is the host components (network.network.network.host). This class provides for large number of networks with fewer hosts per network.
Class D – Used for multicasting.
Class E – Reserved addresses