Describe Variable-Length Subnet Masking (VLSM)

Posted on 10:55 AM by Bharathvn

Similar to the previous question, this is another favorite fundamental question. VLSM is a feature of OSPF, RIPv2, and BGP that enables classless routing. With classful routing protocols such as RIPv1 or IGRP, every autonomous system uses the same subnet mask. For example,,, and are all Class C networks and therefore have a /24 or subnet mask.

VLSM allows an autonomous system to support different subnet masks such as and to support subnets. VLSM also supports “supernetting,” such as describing to include all hosts in and Do not be surprised if you are asked to perform a
few subnet and supernet examples.

For more information on VLSM, Google “VLSM”