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IP Subnetting Step #2: The Key Design Trade-off: Partitioning Network Address Host Bits
(Page 2 of 3)
Class C Subnetting Design Example
Let's take an example. Suppose we
have a Class C network, base address 211.77.20.0, with a total of 7
subnets. The maximum number of hosts per subnet is 25. Looking at the
subnetting summary table for Class C, the answer is instantly clear:
we need 3 bits for the subnet ID. Why? This allows us 8 subnets and
30 hosts per subnet. If we try to choose 2 bits, we can't define enough
subnets (only 4). As Figure 74
shows, if we choose 4 bits for the subnet ID, then we can only have
14 hosts per subnet.
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