In IPv4 the IP addresses are divided into five classes. The first three classes are equipped with a subnet mask, that basically separates the network part of the IP address from its host part. A natural question then arises that why the IP addresses in different classes range between 0-127, 128-191, 192-223, 224-239 and 240-255.
The explanation is simple and has no other strings attached to it other than that. And the explanation is that in the first class (class A) the first bit of the first octet of the address is set to zero and that is why the allowable addresses in this class can only vary between 0-127. Similarly, in class B the first two bits of the first octet of the address should be set to 10 and that is why the addresses can only be between 128-191. Likewise, for class C, D and E, the first octets of the IP addresses have to be set to 110, 1110 and 11110 respectively. Consequently, the IP addresses can only be between 192-223, 224-239 and 240-255 respectively. Please do the binary conversions yourself to verify that this is really the case. Other that that, as one might think, there is no arcane explanation associated with this idea. Please peruse the following article to soothe your curiosity.
IPv4 – Address Classes
IPv4 Address Classes – Internet Protocol hierarchy contains several classes of IP Addresses to be used efficiently in various situations as per the requirement of hosts per network. Broadly, the IPv4 Addressing system is divided into five classes of IP Addresses.
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