In the previous tutorial, we have studied How to do subnetting. We studied how to divide the network into equal parts. Sometimes, we may need to divide a network into unequal parts and for that we need variable length subnet masking. In this tutorial, we will study about variable length subnet masking using an example.

– Assume we wish to divide a network into 3 parts such that –
Network ID – 200.2.2.0
1st part contains 128 addresses.
2nd part contains 64 addresses.
3rd part contains 64 addresses.

– We are dividing the network into 3 parts and thus we need at least 2 bits for subnet. But since the subnet is not divided into equal length addresses, we first divide the network into 2 equal parts, and then further divide one part into another two parts.

– Thus, the range of the divided network:
200.2.2.0 – 200.2.2.127
200.2.2.128 – 200.2.2.191
200.2.2.192 – 200.2.2.255

Variable Length Subnet Marking Example

– Subnet Mask for Subnet 1: 255.255.255.128
– Subnet Mask for Subnet 2: 255.255.255.192
– Subnet Mask for Subnet 3: 255.255.255.192

Note:
– Subnet Mask is same for all subnets in fixed length subnet masking.
– Subnet Mask may be different for subnets in variable length subnet masking.

In the next tutorial, we will study about supernetting with example