Step-by-Step: Setting up Internet Connection Sharing (ICS) in Windows 2000 Professional
Updated: January 13, 2001

Here's how to setup Internet Connection Sharing or ICS in windows 2000.  ICS is useful as long as the host computer is always on.  If the host machine is turned off or rebooted, all of the computers are then disconnected from Internet for that period of time.

Another limitation of ICS is that you are limited to sharing the connection to 10 clients, which may be too few, depending on your needs.  A hardware router solution such as the Linksys 4 port DSL/Cable router can share the connection with up to 253 users.

ICS has many benefits such as being a basic firewall to keep intruders out.  It is also free so you do not need to pay for hardware routers.

The first thing you need to do is install two Network Interface cards (NIC) in your computer.  I suggest that you buy two different brands of network cards instead of two identical ones because Windows will give them the same name.  If you're lucky, Windows may label one card #1 and the other #2.  Once you install both cards (install the NIC, drivers, etc) we need to configure it.

Go to Start -> Settings -> Network and Dial-up Connections and you'll see both NIC's and whichever dial-up connection you have, in my case it is a dial-up to USC's modem pool.

You'll notice that each NIC has it's own name and in our example, it is "3com" and "Realtek".


I find this confusing so I changed the names to "WAN" for Wide Area Network (connects to the Internet) and "LAN" for Local Area Network (the network inside my house).  This is just for my own convenience, you can leave the names alone or call them "Ren" and "Stimpy".  Whatever makes sense to you.


Next, connect your DSL or Cable connection to the network adapter labeled WAN and follow the instruction your ISP gave you.  To configure the NIC, you double click on the "WAN" icon and then click on "Properties".  Here you will be able to install protocols, clients, and setup your TCP/IP.


The after you configure your WAN adapter, you may be required to restart your computer.  After you reboot, you need to launch a web brower to see if you can connect to the Internet.

Assuming that everything worked fine and you were able to connect to the Internet, let's now share this connection across the other network card.

ICS works by  connecting one network card (WAN) to your broadband connection and the other to your home network (LAN) so share the Internet connection.  In order for this to happen, the second network card needs to be connected to a hub or switch which is connected to the rest of your network.

Mentally walk with me through this one:  The connection comes from the mystical wall (DSL or CABLE) and enters your DSL or Cable Modem.  It then goes INTO your WAN network card in your server then OUT your LAN network card to a hub or switch to which the rest of your computers are connected.  Easy yeah?

In order for your WAN network card to share the Internet connection, it acts like as a DHCP Server which basically hands out IP numbers to your LAN computers (client computers).  You must configure each client computer to obtain an IP address automatically from the DHCP Server.  We'll come back to this.

Now were are going to share you connection.  In order to do this, go to your WAN icon and double click on it.  (NOT the LAN icon!)  Hit properties, and you will see two tabs "General" and "Sharing"  When we were configuring the WAN network card for DSL or CABLE modem, we used the "General" tab.  Click on the "Sharing" tab and you'll see this:


Check the box "Enable Internet Connection Sharing for this Connection".


Click "OK".  You will get this warning:


Basically the warning says this computer will now be a DHCP server (this computer will assign IP numbers to the other client computers) and that all your client computers must be set to obtain an IP address automatically.  They cannot be using a static IP address and work with ICS,
Click "OK" to continue.

Network Security
ICS configuration now should work.  Each client computer must be set to obtain a IP address automatically.  Give the client computer a reboot and upon loading, it will get an IP address from your ICS host computer.

Note: ICS does not need to be loaded on the client computers.  Only the computer that is directly connected to the Internet connection needs to have ICS installed.  This was very confusing to me at first!

However, we still need to setup the network for security.  You want to keep your WAN connection very secure, but can relax security on the LAN side.  For example, you want to have file and printer sharing on your Local Area Network, but not across the whole Internet, right?  (Wow, imagine the whole world sharing your laser printer.  That could cost you billions!)

This part is nice and easy.
Double click on the WAN icon -> click on properties.  In the window you will have a list of protocols and services that are attached to that network adapter.  Uncheck every box except TCP/IP.   TCP/IP is necessary to connect to the Internet.  It should look like this:


The LAN network card can have whichever protocols and services you want since it is on your local network.  The only required protocol is TCP/IP, the rest are optional.


One final check before we finish.  Go to the Command prompt: Start -> Programs -> Accessories -> Command Prompt and enter the following:  ipconfig /all

You will see a summary of all your networking information.

Under WAN, you will see the IP address your DSL/Cable host assigned to you or your static IP number.

Under LAN, you see the IP number of 
This is the IP number of your server computer when accessed from INSIDE your network.  ICS will assign each client computer in your network an increment of the original IP number.  (,

Now your whole local area network (up to 10 people) can share one connection to the web.  Hopefully it's a fast one!

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