What is a Dynamically Assigned IP Address?

Every house in the world has an address. Every telephone has a number. And, every computer that connects to the internet also has to be assigned a number so that it can be identified by other computers. Imagine trying to call a phone that has no phone number. It just wouldn't work!

Computer numbers are called IP numbers, which stands for Internet Protocol. The number will be seen as four sets of digits that range from 0 to 255, each separated by a dot. For example 208.77.188.166. The sections of the IP address identify the class of address, the country, and the local network, similar to the way a phone number identifies the country, area code, network, and individual phone. (The system is currently undergoing changes which will allow for many more addresses, due to the explosive growth of the internet. However, that does not affect the question of static vs dynamic addresses).

There are two ways in which computers are assigned their numbers. The method which is most comparable to the telephone number analogy is that each computer is assigned its own number which is forever associated with that computer. This is called a static IP address. A computer with a static IP address will use that number every time it logs into the internet. A user does not often need to know the IP address, but the system that makes all the connections work must know it.

However, the other method in which a computer is assigned a number is by the dynamic method. With dynamic IP addresses, a slightly different number may be assigned to a computer temporarily when it logs onto the internet. This makes it possible for an internet service provider to allow for more computers to log on than the number of IP addresses that they own.

Here is how it works. Not all computers are connected to the internet all the time. When a computer is not connected it does not have to have an IP address. So a service provider may own a range of similar numbers. If Provider Pete owns 208.77.188.0-255, then he has the ability to have 256 computers on line at the same time. However, he might be able to support 1000 customers if no more than a fourth of them are on line at the same time. Each time one of those customers logs in they will be assigned 208.77.188.X, where X is any one of the numbers from 0 to 255 that is not currently logged in.

If a customer of Pete's logs out and logs back in, even immediately, the chances are that the computer will be assigned a different dynamic IP address for that session. This would never work for telephones, because we are so familiar with using people's numbers. But it is a perfect solution for computers because users don't need to know IP addresses.

In short, static IP addresses are permanently assigned to a computer, while dynamic IP addresses my change from one internet session to the next. Which type is assigned rarely matters to the average computer user.

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