Describing the Components of CIDR

In Chapter 7, you learned that the number of bits in the network portion of the subnet mask determines the number of possible networks, and that the number of host bits determines the number of hosts on those subnets. You also learned the formula to calculate these values given the numbers of bits. However, in classful subnetting, with only the three default subnet masks available, you can calculate those values as many times as you like and you always get the following answers:

In this section, you will learn how to create subnet masks that will yield the number of networks you need or the number of hosts you need on each network. You'll also be introduced to Variable-Length Subnet Masking (VLSM) and the additional benefits that can be derived by including this concept in the network design.