In Internet communications, the categorization by the part of an IP address that distinguishes the network address from the host address. Class A addresses allocate 7 bits to the network ID and 24 bits to the host ID. Class B addresses allocate 14 bits to the network ID and 16 bits to the host ID. Class C addresses allocate 21 bits to the network ID and 8 bits to the host ID. Class D addresses contain 1110 in the first 4 bits and identify the address as a multicast. The remaining 28 bits in the class D address specify a particular multicast group.