CCNA Exploration Semester 1-Chapter 6

Classful addressing
Easy to work out but very wasteful.
Routers and hosts still assume class subnet masks by default. Class A /8 255.0.0.0. 23-Jul-12 18.

Class B /16 255.255.0.0.
Class C /24 255.255.255.0.Classless addressing
Any suitable prefix can be used.
We (and devices) need to know what the prefix is. More flexible, less wasteful.