Addresses used on the internet such as for web servers and other network devices are known as public IP addresses.
Public IP addresses need to be purchased for example when hosting a website or provided by your Internet Service Provider (ISP).
With such a huge number of devices in private networks the use of public addresses would quickly extinguish the number of available IP addresses.
To overcome this, a range of Private IP addresses were nominated as non-routable (cannot be used on a public network i.e. the internet) they are:
|Class||IP address range||Default subnet mask||Number of hosts|