When you're studying to pass the CCNA, you're introduced to "private addresses", the address ranges formally referred to as RFC 1918 Private Addresses. (RFC stands for Request For Comment; to see a typical RFC, just put that term in your favorite search engine.)

There are three ranges of 1918 Private Addresses, one in each major network class.

Class A: 10.0.0.0 /8

Class B: 172.16.0.0 /12

Class C: 192.168.0.0 /16

Be careful - these masks are not the classful network masks you're familiar with!

The need for private address ranges arose when we started running out of IP addresses! (A lot of us never thought that would happen, but a lot of us used to think we