At the heart of every Internet enabled network is a modem & router. You may have heard the terms "modem" and "router" used interchangeably and you would be forgiven for thinking a modem is the same as a router. They are often promoted as a single device known as a combined Modem/Router. It is not important to have an in-depth knowledge of either device, however, it is important to understand that they are different.
A modem is responsible for negotiating and keeping a connection to the internet via your ISP network. This could be in the form of DSL, WiMax, cable or any other type of network, but as far as any network device is concerned, there is no difference between them.
A router provides a number of ports that allow many computers or network devices to connect together to share a single Internet connection. The router connects to the modem and relies on it for a connection to the Internet.
Now that we know a little more about modems & routers, let's take a look at what happens when you connect a network device or PC to your router.
Every computer or device on a network requires something called an IP address in order for it to work correctly and to make it visible to other devices on the network. So where does your computer or device get this IP address from?
It is the job of your router to allocate IP addresses to each device connected to your network. It uses a method known as DHCP which dynamically allocates an IP address to each device as it is connected into one of its ports. Your router will have a default IP address and even though 192.168.0.1 is perhaps the most common, it could be quite easily be something like 10.0.0.1
If your router address is 192.168.0.1, the first device that you plug into a port will likely be allocated an address of 192.168.0.2, the second will be given 192.168.0.3 and so on. This allows you to make a calculated guess at what the IP address of a particular device on your network may be, but there are more accurate ways to find out.
On a Microsoft Windows computer, the old fashioned way is to go to the Command Prompt, type in "ipconfig" and press the enter key. The screen will then display several lines of information about the network settings on your PC and the two settings of most interest to you are:
IPv4 Address - the IP address of your computer
Default Gateway - the IP address of your router
A more modern, but perhaps more complex way to find the same information is by checking your network settings from within the MS Windows environment. Annoyingly, Microsoft in their wisdom have changed the way this is done in every version of Windows and it can be difficult finding the settings for your network card. Once you do manage to locate the settings on your particular version of MS Windows, view the properties of your network card and you will see the IP address of your computer and router.
The IP addresses that we have mentioned so far are called internal IP addresses and they can only be used within the internal boundaries of your local area network. You may have heard of external IP addresses, sometimes referred to as public IP addresses - so what are they and how are they different from internal IP addresses?
An external IP address is used to register your modem and network on the Internet. An external IP address will be allocated to your modem during the negotiation of a connection with your ISP. The public IP address of your modem is visible to every computer on the Internet, which might be good for visiting all the great resources that the Internet has on offer, but how do you prevent the unwelcome hackers out there from gaining access to all the devices on your private network?
This is the job of your router and it has a number of technologies at its disposal to prevent this from happening.
There are 2 different ways to find out what the public IP address of your modem is. 1 way is to browse to the web interface of your modem/router and look through the WAN settings. You will need to have a login ID and password to log in to your modem/router and the internal settings can seem quite complicated to an inexperienced user. A much quicker way is to go to a web site that is designed to display a page containing your external IP address when you visit.
One such web site is available at whatismyip.com and it also has a FAQ section on IP addresses which you can use to build on what you have learned from this article.
Source : http://www.goarticles.com by Steve Nutt
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