Subnetting can be one of the most difficult subjects to master for many IT people.  There is a long way to subnet and a very short and easy way.  It is vital you understand how the long way works first but then in real life you will use the short (the easy way).

Address Depletion

Shortly after the IPv4 addressing scheme was implemented it became apparent that there were not enough addresses to meet demand.  More and more organisations were using computers and networking equipment and the current scheme was wasting thousands of addresses.

Example: