Private and Public IP Addresses

Internet Protocol (IP) addresses are of two types: Public and Private.

A router will typically have two network interfaces.

An Internal Interface

An external Interface

Each of these interfaces will have an IP address.

Public IP address

Public IP address (External) is assigned to every device that connects to the Internet where each IP is unique. In this case, there cannot exist two device with the same public IP address all over the Internet. This addressing scheme makes it possible for the devices to “find each other” online and exchange information. User has no control over the IP address (public) that is assigned to the device. The public IP address is assigned to the device by the Internet Service Provider as soon as the device is connected to the Internet.

A public IP address can be either static or dynamic.

Public static some times called Dedicated means the IP address never changes as long as you stay with the same provider.

Public dynamic means the IP address can change from time-to-time.

Private IP address

Private IP address (Internal) means the IP address can only be used by those on the same network. Devices with private IP addresses cannot connect directly to the Internet. Likewise, computers or other devices outside the local network cannot connect directly to a device with a private IP.

An IP address is considered private if the IP number falls within one of the IP address ranges reserved for private networks such as a Local Area Network (LAN). The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private networks (local networks):

10.0.0.0 - 10.255.255.255 (Total Addresses: 16,777,216)

172.16.0.0 - 172.31.255.255 (Total Addresses: 1,048,576)

192.168.0.0 - 192.168.255.255 (Total Addresses: 65,536)

IP Address Terminology

Static means the IP address never changes as long as you stay with the same provider or same server.

Dynamic means the IP address can change from time-to-time.

Public means the IP address can be visited from any computer in the world.

Private means the IP address can only be used by those on the same network.

Shared means other people use your IP address for their connection.

Dedicated means no one else uses your IP address for their connection.

Class identifies the range of your IP address and the default subnet mask.

A class - 0 to 127 with default mask of 255.0.0.0

B class - 128 to 191 with default mask of 255.255.0.0

C class - 192 to 223 with default mask of 255.255.255.0

D class - 224 to 247 (not currently used)

E class - 248 to 255 (not currently used)