# Can someone explain ISP addresses to me?

I have always assumed, without thinking too hard on the subject, that ISP addresses were little numbers that come directly from your computer. I have read how some can be the same, something about AOL? Can someone explain the whole thing to me?
Darby

While you have the IP number, it points uniquely to your machine. However, you get the number from your provider, AOL or whatever. Most ISPs (Internet Service Providers) have fewer IP numbers than they have customers, and so they use what’s called dynamic allocation: When you sign on, the assign you one that’s available at the moment, which you may or may not have had before. The next day, that same number can and probably will be used by someone else. They can do this because there’s no chance that every single AOL user is going to be online at once.
On the other hand, some providers provide static IP addresses, which always stay with the same computer. This is particularly true for universities, DSL, cable modems, and other setups where users are likely to keep their computers hooked up 24/7. Note that even in this case, the IP number isn’t completely fixed to the machine, as it’ll change if you change providers.

Usually, all of the IP numbers available to a given provider will be similar; typically, the first two sets of three digits will be the same. For instanace, all of the numbers for a given ISP might be something like 123.234.xxx.xxx, where the x’s can be variable. The larger providers like AOL might have several sets.

The numbers you are thinking of are called IP addresses. Now I’m going to simplify this a bit, but if you want more details just ask. Explaining the “whole thing” would take a book, but this is what I do for a living. The address are 32-bit binary numbers (don’t worry about what that means)that are usually written as xxx.xxx.xxx.xxx where each ‘xxx’ is a number between 0 and 255 Every computer that is on the internet is assigned an IP address.

Some computers have permanently assigned addresses (static IPs) Since it would be a pain to have to remember that http://www.straightdope.com is actually 67.97.40.3, there exists a way (DNS - the Domain Name System) to translate the names to the appropiate numbers. When you are connected to your ISP, you are assigned an IP from a pool of addresses that they own. So when you are online no one else has the same number as you, but as soon as you sign off the number will get recycled by your ISP. I think that is what you are asking.

There are also some sets of numbers that are reserved for use on private networks. (They begin with 10.xxx.xxx.xxx or 196.168.xxx.xxx for example.) Since these address are not directly part of the public Internet, more than one computer can be using them at once as long as they are not on the same network.

So why have numbers at all? The computers that make up the guts of the Internet use then to know how to route your emails, IMs, web pages around to the appropriate servers to get things where you want them to go. How routing works is a whole other (albeit related) ballgame.

Let me know if this answers your question. There’s a lot more to it than this, so just say the word and I’ll give it another shot.

[Moderator’s note: I fixed the italics. -manhattan]

[Edited by manhattan on 07-11-2000 at 07:35 AM]

(manhatten, no worries - actually, after i originally posted this I did wonder if it sounded a little subversive. Just curious, honest !)

I also have a question on this subject. Understand the distinction between dynamic and static IP’s. However, I also thought that someone coming from a dynamic IP could still be identified if they didn’t unload the cookie before re-visiting. If they unload then there’s nothing with which to match the individual computer.

Some search engine’s set a limit on how many submissions of web pages they will accept from any one source in a given time frame and I’ve thought the combo of dynamic IP’s and unloading cookies got around that.

Never quite understood how the admin’s on a message board like SDMB log IP’s in those circumstances but if anyone can explain it would solve a mystery for me.

Manny - Thanks for the italics fix.

London - Well, as far as I know, if you’ve cleared the cookie, and you’re using dynamic IP, then there is no way to directly identify a particular machine. However, dynamic IPs are not random, they still will identify you as comming from a particular domain, and probably (depending on the size of the domain) as comming from a particular subnet in the domain. If someone is making a nusiance of themselves, or doing something illegal what the sysadmin would do is find out what domain the offending person is comming from and then contact the admins of thier ISP.

Sysadmins tend to be cooperative about these things. (And if they are not, there’s always the possibility of a court order.) Your ISP knows, and probably logs the fact that dynamic IP x was assigned to user y at 10:30 last friday night when the the lowlife scum user lauched his virus/posted kiddie porn, or whatever. So the admin of the offended system calls up the admin of the offender’s and trys to get them to take appropriate action.

The IPs that the admins of the SDMB are logging are most likely just the IPs that the messages come from whether static or dynamic.

If you want more info from this site, note that you can’t search on “IP”, as it doesn’t index short words. “ISP” should be long enough. Search on that in the subject only.

Thanks for the explanation, Minkman. Been curious about that for some time. So it seems that unless you’re particularly switched on, everything is ultimately traceable whether via a dynamic ISP or a fixed ISP system admin. Kind of reassuring and scary at the same time.