The class A address range

The class A network has the high-order bit set to zero. It includes address ranges from 0.0.0.0 to 128.0.0.0. It has an 8-bit prefix for network IDs (/8) and a subnet mask that is equivalent to 255.0.0.0. The 0.0.0.0 network is reserved for special purposes and 127.0.0.0 is reserved as a loopback address range, which leaves 126 out of 128 possible network IDs for use. The reservation of a whole 127.0.0.0 network ID for a loopback address is an obvious example of extremely bad address assignment planning. This bad planning originated in the early days of the internet; back then, we could not imagine how big and important the internet would become and how the explosion of interconnected devices would lead to the depletion of the IPv4 address space. The class A has 128 network IDs and 16,777,216 possible host addresses.

The following screenshot shows the structure of a class A address: