An IP address is a string of four numbers, each between 0 and 255, separated by periods, that is used by computers on the Internet to talk to each other. Because there aren't an unlimited number of IP addresses, most ISPs have fewer IP addresses than they have customers. For this reason, they need to assign each customer an IP address from a pool of currently available addresses each time the user logs on. While this method allows Internet Service Providers to conserve IP address use, it means that users won't have the same address each time they log in, and therefore can't have any single domain name consistently point to their IP address. This fact prevents users from having maximum power over the Internet. Having a dynamic IP address means that you can only contact other computers on the Internet; you cannot have them connect to your computer. One consequence of this fact is that you can't have servers (web, ftp, telnet, irc, etc.) run on your computer.