The document provides a 4-step process for calculating VLSM using an example IP address of 192.168.100.40/27. The steps are to determine the subnet mask, identify the network and broadcast addresses by filling the first three octets, determine the valid IP range, and calculate the number of hosts.

1. 1
Post prepared by : MD. SHIHAB HOSSAIN. (IDB-BISEW), Cell: 01750006844,
Mail: shihabmsh@live.com
VLSM Short-cut
I hope this post will guide you to calculate VLSM very shortly. Also you don’t have to
remember binary for every number except subnet mask.
I take an IP address, for example: 192.168.100.40 /27
Step 1 : Subnet Mask

2. 2
Post prepared by : MD. SHIHAB HOSSAIN. (IDB-BISEW), Cell: 01750006844,
Mail: shihabmsh@live.com
Step 2 : Network Address and Broadcast Address
Fill first 3 octets with IP Address.

3. 3
Post prepared by : MD. SHIHAB HOSSAIN. (IDB-BISEW), Cell: 01750006844,
Mail: shihabmsh@live.com
Now the first number of the block is Network Address and Last number of block is Broadcast
Address.
Step 3 : Valid IP Range

4. 4
Post prepared by : MD. SHIHAB HOSSAIN. (IDB-BISEW), Cell: 01750006844,
Mail: shihabmsh@live.com
Step 4 : Number of Hosts