You follow the same steps in performing VLSM as you did when performing classical subnetting.
Consider Figure 2-1 as you work through an example. Figure 2-1 Sample Network Needing a VLSM Address Plan
27 Hosts B
12 Hosts C
12 Hosts D
A Class C network—192.168.100.0/24—is assigned. You need to create an IP plan for this network using VLSM.
Once again, you cannot use the N bits—192.168.100. You can use only the H bits. Therefore, ignore the N bits, because they cannot change!
The steps to create an IP plan using VLSM for the network illustrated in Figure 2-1 are as follows:
Step 1 Determine how many H bits will be needed to satisfy the largest network.
Step 2 Pick a subnet for the largest network to use.
Step 3 Pick the next largest network to work with.
Step 4 Pick the third largest network to work with.
Step 5 Determine network numbers for serial links.
The remainder of the chapter details what is involved with each step of the process.
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