Internet Protocol (IP) Address is an unique number that is assigned to your computer or any device for that matter, like your smart phone, router or printer, when it is connected to a computer network (eg. internet). There are usually two types of networks that you could be directly connected to, an internal network or the internet. If your computer connects to a router (or is part of a wider company network) then your are connected to a internal network. If your machine connects directly to the modem that is provided by your ISP (Internet Service Provider), then you are directly connected to the internet.
But computers can also be given names and websites have names so why not just use the names? Well, both are important. The name needs to be both unique as well as memorable which is almost impossible to achieve with just letters and alphabets. For the same reasons that we have both a personal name as well as a unique social security number, there is a machine name as well as an IP address. If we were to just use numbers, you will have to always remember the 12 digit number for all the websites, like yahoo or google. Also, computers are much better and faster at crunching numbers than they are at processing words or names which makes dealing with numbers faster.
Even if you are only directly connected to an internal network, you could still be connected to the internet via the router. In this case, you are connected to the internet using a router which connects on your behalf. It is the router which holds the public IP address while your machine holds a local IP address. All machines in the local network shares this same public address. In case you are directly connected to the internet, the local and public IP address are the same for your machine.
The internal or local IP address is provided by your router while the public IP address is assigned by your ISP. It is generally assigned in blocks with in a given region, which means given an address it is possible to track the address to the general vicinity of the machine, usually down to the city. Your IP address and other information is recorded by all web servers and law enforcement or authorities will be able to track it down to the exact machine. So, no matter what anyone says there is really no anonymity on the web.
Almost all ISPs use what is called a Dynamic Host Configuration Protocol (DHCP) to assign public addresses. It is assigned from a large pool of available numbers every time your device connects to the internet. This is done dynamically so that the numbers can be reused for different machines at different times. The machine is given a unique number for a defined period of time which is called the lease time and the same IP address may or may not be re-assigned after the lease time is expired.
Why do you need an IP Address
Your computer needs to have an IP address so that it can receive information from other devices on the network. This is usually the information that you requested such as a website page, and the sender (ie, the website) needs to know where to send the web page. It works very similar to a telephone number or a postal address. As a caller needs to know your unique phone number to call you, the computer needs to have an unique identifying number so that other devices can send information to you.
There is usually at least three different IP addresses that is associated with your computer.
Loopback : The first is a loopback network interface which is usually assigned 127.0.0.1. This allows your machine to basically talk to itself. The name localhost is mapped to this address.
Local Network IP: Next one is the internal IP address or the LAN (Local Area Network) address. This is the address which is assigned to your computer by your router and is private to your network. This usually is in the block of 192.168.xxx.xxx. It could be be 192.168.1.100 or any thing which starts with 192.168. This allows your computer to talk to the router and the router to talk back to your computer.
Both the loopback and local IP addresses can be reconfigured to pretty much any number as they are local to your network. The values provided are usually the default based on convention.
Public IP: The next one is the external address or the public IP address. This is usually assigned to the router in your network which allows it to talk to other computers outside of your network and on the internet on your behalf. The router forwards the requests from your computer and forwards the response back to you. If you happen to have more than one network card on your machine, then it is possible to have even more addresses assigned to your computer.
Where and How to Find the Local IP Address
On a Windows operating system, you can right click on your connection icon and select Status, which will open a dialog with the network details. Click on the support tab to view the status of your connection. You can view more details about your connection by clicking on the Details button.
In this example, your local IP address is 192.168.1.106 while the local IP address of the router is 192.168.1.1.
Another option to find your local IP address is with the ipconfig (Internet Protocol Configuration) command. Open a DOS command window on your machine and type in the command
The output of the command will you all the network information like the host name, IP address, subnet mask etc. The value shown next to IP Address is the local address of your machine. The value next to the Default Gateway is the local address of your router, which is also your DHCP server.
If you are on a Linux or Unix machine, the equivalent command is ifconfig. Typing in the command ifconfig -a will display all the network details.
Where and How to Find the Public IP Address
Internet Websites: If you have an internet connection, the easiest way is to check one of the websites which shows your IP address. Doing a Google search for “what is my ip” will show you quite a lot of websites, one such website is FInd IP Address, which will show your entire information based on your IP address.
Router Status Page: If you have access to your Router administration pages, you can check the Router Status Page which will display all your public IP information. The page url will vary depending on your router. For a linksys router, the URL is Router Status Page (192.168.1.1/StaRouter.htm).