Just as telephones are identified by unique telephone numbers, computers on the Internet are identified by unique series of numbers called "IP addresses". IP stands for Internet Protocol. Each IP address consists of four numbers separated by three periods; for example, "".




Whenever your computer talks to another computer on the Internet - such as when you visit a web site - the name of the other computer must be converted into an IP address before communication can take place.


Most computers automatically get their IP addresses from the network; that is, they are "dynamically assigned" by an Internet Service Provider or IT department. The technologies that make this possible are "DHCP" ("Dynamic Host Configuration Protocol") and "PPP" ("Point to Point Protocol"). Fortunately, most modern operating systems handle DHCP and PPP without much effort on the part of the user. The only disadvantage of a dynamically-assigned IP address is that it can change each time you connect to the Internet. If you have a continuous connection to the Internet, your Internet Service Provider may assign you a "static IP address".


static IP address identifies your computer on the Internet using the same address as long as you remain with the same ISP. This is necessary if your computer is to provide services on the Internet, such as e-mail or web hosting. If your computer is located behind a firewall, the firewall may be hiding your computer's actual IP address from outside world. In that case the IP address is actually the IP address of the firewall, not your computer. Similarly, if your computer is behind a "proxy server" or "web cache" (i.e., a computer that intercepts requests for web pages in order to speed up frequently requested pages), the IP address is probably the IP address of the proxy server or web cache - not your computer when you check your IP address online.