Introduction to Networking

Subnetting In ClaasFul IP Addressing

As we already know, classful subnetting is also called Fixed-length subnetting. The Fixed-length subnetting contains the following properties.

• The sizes of all sub-networks are the same.
• Subnets of all subnetworks are the same.
• All the sub-networks have an equal number of hosts.

Let’s understand with an example

Example-01

Suppose

• We have a big single network with IP Address 205.10.20.0.
• We want subnetting. So, divide this network into 2 subnets.

As the given IP belongs to Class C So, 24 bits are used for net ID, and 8 bits are used for Host ID.

To create two subnets (subnetworks) and to represent their subnet IDs, we require 1 borrowed bit from the host part.

So,

• We borrowed one bit from the Host part.
• If borrowed bit = 0, then it will represent the first subnet.
• If borrowed bit = 1, then it will represent the second subnet.

Note: After borrowing one bit, Host ID part remains with only 7 bits.

IP Address of the two subnets are

• 10.20.00000000 = 205.10.20.0
• 10.20.10000000 = 205.10.20.128

For First Subnet

• IP Address of the subnet = 205.10.20.0
• Total number of IP Addresses = 27= 128
• Total number of hosts = 128 – 2 = 126
• Range of IP Addresses = [205.10.20. 00000000 to 205.10.20. 01111111] = [205.10.20.0 to 205.10.20.127]
• Direct Broadcast Address = 205.10.20.01111111 = 205.10.20.127

For Second Subnet

• IP Address of the subnet = 205.10.20.128
• Total number of IP Addresses = 27= 128
• Total number of hosts = 128 – 2 = 126
• Range of IP Addresses = [205.10.20.10000000 to 205.10.20.11111111] = [205.10.20.128 to 205.10.20.255]
• Direct Broadcast Address = 205.10.20.11111111 = 200.1.2.255