16.32.0/20 to give you more network addresses and fewer hosts per network. If, for
example, you subnet 172.16.32.0/20 to 172.16.32.0/26, you gain 64 (26) subnets, each of which
could support 62 (26 ??“ 2) hosts.
Figure 3-31 shows how subnet 172.16.32.0/20 can be divided into smaller subnets.
Figure 3-31 Calculating VLSM Networks
The following procedure shows how to further subnet 172.16.32.0/20 to 172.16.32.0/26:
Step 1 Write 172.16.32.0 in binary form.
Step 2 Draw a vertical line between the twentieth and twenty-?¬?rst bits, as shown
in Figure 3-31. (/20 was the original subnet boundary.)
1st subnet:
2nd subnet:
3rd subnet:
4th subnet:
5th subnet:
Network Subnet Host VLSM
Subnet
172 . 16
172 . 16
172 . 16
172 . 16
172 . 16
.0010
.0010
.0010
.0010
.0010
0000.00
0000.01
0000.10
0000.11
001.00
000000 =
000000 =
000000 =
000000 =
000000 =
172.16.32.0/26
172.16.32.64/26
172.16.32.128/26
172.16.32.192/26
172.16.33.0/26
Subnetted Address: 172.16.32.0/20
In Binary 10101100. 00010000.00100000.00000000
VLSM Address: 172.16.32.0/26
In Binary 10101100. 00010000.00100000.00000000
Implementing Variable-Length Subnet Masks 127
Step 3 Draw a vertical line between the twenty-sixth and twenty-seventh bits, as
shown in the ?¬?gure.
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