CIDR is used within the Internet. Its counterpart within an organization is the Variable-length subnet mask
(VLSM). Like CIDR, VLSM allows you to allocate the required host bits on a granular basis. In other
words, it allows you to provide only the bits required to address the number of hosts on a particular
subnetwork. Like CIDR, VLSM requires a routing protocol that supports the sending of the subnet mask in
its updates. The routing protocols that support VLSM are: RIPv2; OSPF; IS-IS; EIGRP; and BGP-4. The
routing protocols do not support VLSM are: RIPv1; IGRP; and EGP.