IP addresses are like real-world addresses, they are identifiers for computers or devices connected to TCP/IP networks. The entire TCP/IP networking protocol is based on the concept of a unique IP address for every object connected to the network. Messages sent via TCP/IP networks are routed to their destination based on the IP address.

IP addresses have a fairly simple format. They are made of four octets (8 bits), separated by periods. An octet can be from 0-255 (the first octet cannot be 0), with the exception of a few reserved patterns (127.0.0.1 should always resolve to the local machine).

Private networks, such as internal LANs can have any IP addresses they want as long as each is unique, however, to connect to the public and regulated Internet, you will need to use a registered IP address (distributed by the various Internet registries: ARIN, RIPE, etc.)

The number of available addresses in an IPv4 set up is slightly over 4,000,000,000, however, around 20,000,000 are reserved for special uses such as private networks. As more and more users and objects (with the VoIP revolution, as well as kitchens and cars becoming more and more connective, this problem will continue to become more severe) we are quickly closing in on the maximum number of IP addresses available. Thus, IPv6 was devised.

IPv6 uses significantly longer addresses: being 128 bits wide, IPv6 addresses can have 2128 different addresses, or according to Wikipedia: If the earth were made entirely out of 1 cubic millimeter grains of sand, then you could give a unique address to each grain in 300 million planets the size of the earth.

On to actually finding your IP address there are various ways to do it, and each can be wrong for the actual IP address you are looking for. Many people do not connect directly to the Internet, some go through corporate proxies, some go through server provider compressing or caching proxies, and many use proxies for other reasons. This makes finding an IP address significantly more difficult than one would expect.

Sites such as WhatIsMyIP.com provide an output of what that server sees as your IP. This works perfectly if you are not going through any external devices, however, if your Internet access is routed through a proxy, theres a good chance that WhatIsMyIP will show the proxy address, rather than your own, personal address.

On Windows 95 and 98 users may run the executable winipcfg.exe (to do this, go Start->Run then enter winipcfg.exe), which will show information about their connection. IP addresses consisting primarily of 255s, 0s, 1s, 192s, or 128s are likely masks or internal addresses, not the external address you are interested in finding.

On Windows NT/XP users may run ipconfig.exe, however, this is no longer a graphical program. To do this, you must run a command prompt (Start->Run->cmd.exe) then type ipconfig.exe within the command prompt. This will give you a range of output regarding your current connection information. For more help, run ipconfig.exe /? for a help output.

Depending on the Linux distro (and various other things), Linux users may run `ifconfig -a` at a terminal for networking information.