What is a private IP address and what are the private IP ranges?

Any IP address that falls specified ranges is a private IP address and is non-routable on the Internet.

These addresses are reserved for use only within private/corporate network and cannot be seen outside the private networks. These private addresses are translated at the company's firewall into an external (public) IP address, which will be some address that does 'not' fall within these ranges. – – –

An address is Private if it starts with:

10 or
192.168 or

It is possible for anyone to see their external (public) IP by going to any one of a number of sites that provide this information as a free service. One example that's easy to remember is http://whatismyip.com.