Private IP Addresses

Some groups of IP addresses are reserved for use only in private networks and are not routed over the Internet. These are called private IP addresses and have the following ranges:

   10.0.0.0 - 10.255.255.255

 172.16.0.0 - 172.31.255.255

192.168.0.0 - 192.168.255.255

Home networking equipment/devices usually are configured in the factory with an IP address in the range 192.168.1.1 to 192.168.1.255.

You may be wondering how devices using private addresses could ever access the Internet if the use of private addresses on the Internet is illegal. The situation gets even more confusing if you consider the fact that hundreds of thousands of office and home networks use these same addresses. This must cause networking confusion. Don't worry, this problem is overcome by NAT. 

The localhost IP Address

Whether or not your computer has a network interface card it will have a built-in IP address with which network-aware applications can communicate with one another. This IP address is defined as 127.0.0.1 and is frequently referred to as localhost. This concept is important to understand, and will be revisited in many later chapters.