Internet Protocol (IP) is the naming scheme that gives each device on a TCP/IP network a unique descriptor. Because unique identification is the only way to find a device, such as a PC, there is a mathematical limit to the number of unique devices that can exist on the mother of all networks, the Internet.
Now when TCP/IP was developed, it was for military use, and the idea of several or even dozens of devices that would need unique numbers in every home and business in the world (and beyond) was not a consideration. Yet, that is where we are going, and several workarounds have been developed to handle the limitation of only so many numbers being available to give out publicly.
One workaround was to take three number groupings and declare them private. That means you are free to use them on your network at home or work, without directly being part of the Internet. They will never conflict with the numbers assigned to anyone elses computers on the Internet, because by definition, they are private to the individuals or companys own network, and not shared with the Internet.
This allows re-use of the same set of numbers without conflict. To make each network using the same numbers privately have Internet access, the network uses a single public number that is unique as the doorway or gateway to the Internet.
A process known as Network Address Translation (NAT) takes all requests from the private numbers and sends them through the unique and public IP number. This would be called the gateway.
The second workaround that conserves the available numbers is to loan a publicly available number only for as long at the connection to the Internet is required.
For example, think of an Internet Service Provider (ISP) such as Earthlink. They may have 200 modems available to accept calls from the customers in Seattle. That would mean they need 200 IP numbers. And if they had 200 modems, they probably have 2,000 customers. Not all the customers could or typically would want to dial in at the same time.
When a customer connects to a modem at Earthlink, the customer would be loaned an IP number from a computer setup to manage this process. That computer is running a Dynamic Host Control Protocol (DHCP) server. Like a file server, whose purpose is to hand out files to clients, the purpose of a DHCP server is to hand out IP addresses to clients.
The DHCP server would in effect, allow the clients to borrow a cup of IP. As soon as the customer hangs up, the unique number is returned (lease cancellation or expiration) to the available set of numbers, for reuse by another client. This is another conservation workaround.
DHCP doesnt address the fact that IP numbers such, as 10.9.8.2 are not very easy for humans to remember. It wouldnt make a great commercial to hear a jingle telling you to visit www.192.168.254.168.com.
The solution to the fact that humans are more math challenged than computers is next.
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