IP Subnetting Tutorial

This tutorial explains the basic concepts of IP subnetting and its need.

What is IP subnetting

IP subnetting is the process by which multiple network addresses are created from a network address. In this case, the network which is used to create the different networks is known as Major network and the networks which are created are known as subnetted networks.

What is the use of IP subnetting

IP subnetting evolved as there was depletion of IP addresses on the internet space. Intially there was class full addressing where there were standard addresses like class A, class B and class C network. The subnet masks , of each of these networks were constant which was unique for each class. To mitigate the problem of depleting IP addresses, IP subnetting was used, where network addresses corresponding to each classes were used for creating small subnetted networks.

How is IP subnetting performed.

To understand the working of IP subnetting a network address is dissected. Assuming that a network address of 192.168.1.0 and subnet mask 255.255.255.0 is required to be subnetted.In the network address, the part 192.168.1 is referred to as the network portion and .0 is referred to as the host portion. This is derived from the subnet mask. The bits corresponding to 1’s on the subnet mask is the network part and the 0’s would be the host part. There are 8 bits available on the host part, which are available for borrowing. The borrowing is performed from the right to left.

Case Study

Assume that the network, 192.168.1.0 has to be subnetted into two networks. By borrowing 1 bit from the host, we can create two networks (as each bit has two combination’s, 0 &1). But the 1st address and the last address cannot be used as they are respectively used for the network address and broadcast address. For ex, the first address of the network (which is not subnetted) 192.168.1.0 is the network address and the last address would be 192.168.1.255 which is the broadcast address. So to create two network we require to borrow atleast two bits from the host potion, 2*2 -2 = 2 (2 is reduced for the network and broadcast address. )

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