IP originally defined network addresses as 32-bit binary addresses generally represented as 3 digit decimal numbers separated by periods. Since each section or octet of the address represents an 8 bit byte, the highest number that can be placed in the octet is 255 (28 – 1).
But not all 32-bit IP addresses are available. Five different types of networks were reserved in the original scheme, referred to as Class A,B,C,D and E networks. These network classes are as listed in Table 17-2.
|Class||Range||Max. Networks in Class||Max. Hosts|
|A||0.0.0.0 to 127.255.255.255||126||over 16 million|
|B||126.96.36.199 to 188.8.131.52||16384||65534|
|C||192.0.0.0 to 184.108.40.206||2097152||254|
|D||220.127.116.11 to 18.104.22.168||<for multi-cast> ...|