IP numbers

What’s the matter with Internet Protocol (IP) addresses? Do those numbers really signify every PC linked to the internet on the world? When I got online, I never registered anywhere, I simply found out one day that I had an IP number, so there can be no central allocating authority. But if they are assigned decentrally, what’s the system behind it, and how does it avoid duplication?

I’ll let others explain it more thoroughly, but a short part of the answer is that you get your IP number from your ISP when you log in. Unless you pay extra for a static IP, that is.

Your ISP has a block of IP addresses allocated to them by a registry, most likely ARIN. Your ISP then assigns one of those IP addresses to you when you connect to their network. That’s the gist of it.

Actually, IP numbers are assigned by a central authority. I believe it is the NIC (Network Information Center) that does this. However, they do not assign single addresses to individual computers. They assign “chunks” of addresses to networks, and the networks will subnet their allocated chunks.

The most common type of IP address today is IP version 4, which uses 32 bits (4 bytes) of data for each IP address, which is usually written in dotted-decimal notation (4 numbers separated by decimals, each number in a range from 0 - 255 – the range of one byte).

Current IP numbers will eventually run out, and the new standard (which networks will be eventually switching to step by step) is IP v.6, which use addresses 16 bytes long (128 bits), which will supply an effectively unlimited number of IP addresses.

The current IP address scheme divides addresses into several categories, or classes. Class A addresses use the first byte (or first numeral) for the network number and the other 3 for the host number. Class B splits it 2 bytes for network, 2 bytes for host. Class C uses 3 bytes for network, 1 for host.

For instance, in a class C network, the first three numbers of the IP address denote the “chunk” of addresses assigned to the network. For instance, suppose the network number is: 200.23.34. Then this network owns the chunk of addresses from 200.23.34.0 through 200.23.34.255. Each individual number in this range can be assigned to a single host (i.e. a single computer, for instance).

Now, as for your IP number. Depending on what kind of connection you have, it might be fixed or it might be variable. If you have an internet service where you dial up on a modem, then you are getting what is called a “dynamic” IP address. This means that you are assigned an IP address temporarily for the duration of your connection.

Pretend that the Class C network in my example above is your dialup service. Then they can have up to 254 people logged on to their system at one time (the 0 and 255 host addresses are usually reserved). (If you are person 255 trying to dial in, you are SOL until somebody logs off). One day you might dial up and get 200.23.34.15 and another day you might be 200.23.34.140. You’ll always be on the same network number, but your host number would be variable.

If you have DSL or Cable modem, you might have a static (fixed) IP, but this is still assigned by your DSL or Cable provider. They would have chunks of numbers, and the main authority would assign THEM these network chunks. But, they would assign the specific host number to you.