IPv4 Network Classes

The three most commonly used IPv4 network classes are A, B, and C. Each class uses the 32-bit space assigned to the address differently, allowing for more or less IP addresses.

Class A

Class A networks utilize the first eight bits of the address as the “network part.” The last 24 bits make up the host part of the IP address. The network part can fall between 0 and 127, for an example 64.8.12.2, the value “64” in the first byte means that the address is on a class A network. The last bytes (“8.12.2”) make up the “host” part. There are only 127 class A networks exist, but each one allows for up to 16,777,214 IP addresses.

Class B

Class B networks utilize the first sixteen bits of the address for the “network” part, and the remaining sixteen are the “host” part. The first byte of a class B network address can be in the range 128-191.

Class C

Class C networks use 24-bits for the the “network” part, and the last 8 for the “host” part. Class C networks are useful smaller networks – the maximum number of IP addresses being 254. The first byte of an class C IP address can be between 192-223, and the second between 1-255.