Classful Routing, VLSM, and CIDR

In this book, I religiously stick to a classless point of view. Classful behavior and archaic routing protocols supporting only classful routing have disappeared almost entirely.

Variable length subnet mask (VLSM) enables us to think and route beyond the limited view of address octets, and classless interdomain routing (CIDR) enables us to form aggregates and summarize prefixes. A prefix is a network/bitmask representation of a classless network, such as