CCNA Data Center DCICN 640-911 Official Cert Guide

One Size Subnet Fits All (Or Not)

The final choice in the initial planning step is to decide whether you will use a simpler design by using a one-size-subnet-fits-all philosophy. A subnet’s size, or length, is simply the number of usable IP addresses in the subnet. A subnetting design can either use one size subnet, or varied sizes of subnets, with pros and cons for each choice.

Defining the Size of a Subnet

Now think for a moment like the person who chooses the subnet design. To do so, the engineer assigns each subnet a subnet mask, and that mask, among other things, defines the size of that subnet. The mask sets aside a number of host bits whose purpose is to number different host IP addresses in that subnet. Because you can number 2^x things ...