2.4 Variable-Length Subnet Masks
2.4.4 VLSM example
The main figure shows a VLSM example used to optimize the number of possible addresses available for a network. Because point-to-point serial lines require only two host addresses, you want to use a subnetted address that will not waste scarce subnet numbers.

In the figure, the addresses used are those generated in the earlier section "Calculating VLSMs." The figure illustrates where the addresses can be applied, depending on the network layer, and the number of hosts anticipated at each layer. For example, the WAN links use Class B addresses with a prefix of /30. This prefix allows for 16,382 subnets (214-2) and only two hosts (22-2) --- just enough hosts for a point-to-point connection between a pair of routers.

Lab Activity
  In this lab, you will learn how to create an addressing scheme using variable length subnet masking (VLSM).