Classful Networks

When IPv4 (IP version 4) was released the designers thought to divide network in classes. At that time there were 3 classes. In IPv4, IP address has 2 parts, one is the network address and the other part is the host address. What will be the network and host part of the IP is the deciding factor in classful networks.

Class A

If the IP is of the form W.X.Y.Z then in class A networks, W is the network address and X.Y.Z is the host address. So, if you are planning to maintain a Class A network following should be the configuration.

IP address: 10.0.0.2
Netmask: 255.0.0.0
Gateway: 10.0.0.1

The total number of hosts available in this class are 256 * 256 * 256 (you can do the math). So, this class is used for networks with large number of hosts.

Class B

In class B networks, W.X is the network address and Y.Z is the host address. So, if your network is Class B then your configuration should look something like this.

IP address: 10.0.0.2
Netmask: 255.255.0.0
Gateway: 10.0.0.1

Total Number of Hosts: 256* 256

Class C

In class C, the first 3 W.X.Y consitute the network address and Z is the host address. So, if you are planning to form a Class C network then your configuration should look like this

IP address: 10.0.0.2
Netmask: 255.255.255.0
Gateway: 10.0.0.1

Total Number of hosts in this network are only 256. So, they are used for small networks.

As you can see the Netmask changes accordingly. Please make sure that you use the appropriate configuration after choosing a network class. You can use any IP in place of the gateway and make sure that the network part of the gateway and your IP should match for all classes. e.g.

If you have a Class A network and your gateway's IP is 192.168.36.1 then the network part of the IPs in your private network should be 192 (like your system's IP could be 192.0.0.2 this will work for class A),

for Class B the network address for both should be 192.168 (like your system's IP could be 192.168.0.2 this will work for Class B)

and now you can guess that for Class C both the network address should be same and 192.168.36 (like your system's IP could be 192.168.36.2 for Class C).