(In fact, if they follow industry practice, they probably only have 500 or so phone lines anyway.) So that ISP may only have 600 or 700 IP addresses — enough to provide one for each phone line, a few for internal use, a few for future growth, but nowhere near one for each of those 3000 customers.Or maybe you have a cable modem, though “Big Cable Co Inc.” Whenever your cable modem goes online (when you first plug it in and turn it on), it broadcasts a request for an open address, and some computer in their office eventually answers.To a human, names like that (or ibm.com, or yahoo.com, or any of the other four million domain names registered) make perfect sense. Computers use IP addresses (“dotted quad” numbers like .255) to talk with each other on the Internet.
Suppose you have a normal, per month, Internet dialup account from “Some Local ISP, Inc.” They have three thousand customers, but it’s rare that all of them are online at the same time.The Internet is divided into literally millions of domains; each one has its own name.DNS helps to translate that name into an actual location (IP address).If you just want to get online, check your email, look at a few Web sites, maybe get in a quick game of Unreal Tournament 2003, your specific address doesn’t matter.You’ll get a fresh address every time you dial in, that’s all yours for as long as you stay connected, and since other people aren’t trying to connect to your computer, you’re all set.
(These ‘leases’ usually only last for a few days, and sometimes only a few hours.) At the end of the lease, you may be able to negotiate a new lease, but you can’t be sure of it. Your ISP, cable company, or whoever, might let you have a dedicated IP, but they’ll probably charge you extra for it.