IP Address Classes

An IP address is the unique 12 digit number sequence used to identify you over the internet. Every addressing system needs to adhere to some rules so that unique identification can be made easier. As defined by the IEEE committee, an IP address must inform the internet as to what workstation it is part of and which particular node it is of. An IP address class is a series of five different ranges, an IP of which tells the internet how big the network is.
The five different classes are –
• Class A – 1.0.0.0 – 127.255.255.255
• Class B – 128.0.0.0 – 191.255.255.255
• Class C – 192.0.0.0 – 223.255.255.255
• Class D – 224.0.0.0 – 239.255.255.255
• Class E – 240.0.0.0 – 255.255.255.255
Classes A, B and C identify workstations, switches, routers and other devices. Classes D and E identify special computers. For identification of classes, the first four numbers are sufficient. Once we find out which class the IP is from, it is easy to determine the network ID and the node ID.
The classes are an estimation of network size. Class A is for very big networks, class B is medium sized network and class C is for very small networks.
Network ID and Node ID
The very existence of classes is to supply these two pieces of information. An IP address tells us which network it is a part of (Network ID) and the individual computer it is of the network (Node ID). A host ID is a single term used to combine these two ID concepts. Depending on which class the IP address is from, the host ID corresponds to a different sequence of numbers.
• For class A, the last 9 numbers are the host ID numbers.
• For class B, the last 6 numbers are host ID numbers.
• For class C, only the last 3 numbers are host ID numbers.
As you can now see, the greater the number class, the more the number of networks possible for that class, and the lesser the number of nodes in that class. For example, only 128 networks are possible for class A, though nine numbers are available for node and network IDs, implying a very large number of computers. This is exactly the opposite for Class C, since a large number of networks are present, but a very few number of nodes per network.