(The original /20 subnet boundary is extended six bits
to the right, becoming /26.)
Step 4 Calculate the 64 subnet addresses using the bits between the two vertical
lines, from lowest to highest in value. Figure 3-31 shows the ?¬?rst ?¬?ve
subnets available.
VLSMs are commonly used to maximize the number of possible addresses available for a
network. For example, because point-to-point serial lines require only two host addresses, using a
/30 subnet will not waste scarce IP addresses.
In Figure 3-32, the subnet addresses used on the Ethernets are those generated from subdividing
the 172.16.32.0/20 subnet into multiple /26 subnets. The ?¬?gure illustrates where the subnet
addresses can be applied, depending on the number of host requirements. For example, the WAN
links use subnet addresses with a pre?¬?x of /30. This pre?¬?x allows for only two hosts: just enough
hosts for a point-to-point connection between a pair of routers.
Figure 3-32 VLSM Example
172.16.32.0/26
50 Hosts
172.16.32.64/26
50 Hosts
172.16.32.128/26
50 Hosts
172.16.32.192/26
50 Hosts
172.16.33.0/30
2 Hosts
172.16.33.4/30
2 Hosts
172.16.33.8/30
2 Hosts
172.16.33.
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