OSPF Network Design Solutions, Second Edition

VLSMs

The basic concept of VLSMs is to provide more flexibility by dividing a network into multiple subnets. The trick to using this technique is ensuring that you have an adequate number of hosts allocated per subnet.

Note

Not every protocol supports VLSM. If you decide to implement VLSM, make sure that you are using a VLSM-capable routing protocol, such as OSPF, BGP, Enhanced IGRP (EIGRP), Intermediate System-to-Intermediate System (IS-IS), and RIP Version 2 (RIP-2).

OSPF and static routes support VLSMs. With VLSMs, you can use different masks for the same network number on different interfaces, which enables you to conserve IP addresses for better efficiency. VLSMs do this by allowing both big subnets and small subnets. As previously mentioned, ...