Classes of IP Address: Understanding IP Address Classification

In the realm of networking, understanding the classes of IP Address is fundamental. The classes of IP Address actively define device assignment and grouping within a network. By exploring the intricacies of classes of IP Address, we uncover the structure and hierarchy supporting Internet communication. Let’s explore the significance and distinctions of classes of IP Address in this insightful discussion.

From 1981, the Internet used a classful network addressing architecture. it dividing IPv4 into five address classes based on the leading four bits.

Classful IP Classes are based on the default Class A, B or C (Network) subnet Mask

- Class A: 0 - 127 with a mask of 255.0.0.0 (/8)
- Class B: 128 - 191 with a mask of 255.255.0.0 (/16)
- Class C: 192 - 223 with a mask of 255.255.255.0 (/24)

All devices in the same routing domain must use the same subnet mask. Since routers running a classful routing protocol do not include subnet mask information with routing updates, the router assumes either its own subnet mask, or defaults to the classful subnet mask.

Classless on the other hand, allows the use of variable length subnet masks, or VLSM, because subnet mask information is included with routing updates. You can have a mixture of different subnet masks in the same routing domain:

- 10.1.0.0/19
- 10.2.0.0/20
- 172.16.8.0/21
- 172.16.16.0/24

Also remember that not all routing protocols support the “Classless” addressing. Take RIP version 1 for example it only supports Classful routing. All others like RIPv2, EIGRP, OSPF and IS-IS support both classful and classless routing.