When designing a network using VLSM, the following simple steps can help come up with an appropriate addressing scheme:
Start by finding the largest subnet in your network. The number of host addresses needed decides the size of the subnet.
Next assigning an appropriate mask to the largest subnet using the block sizes mentioned in Table 2-9.
Note the subnet numbers remaining with the mask used in Step 2.
Take the next available subnet and subnet it further to accommodate your smaller subnets.
Write down your new subnet numbers again.
Repeat step 4 and 5 for smaller segments.