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Configuring Internet connection sharing (ICS)

I'm using Win2000 Server but I can't configure NAT. I have an U.S. robotic modem and a LAN. My ISP hasn't given me a public IP and I'm behind a proxy (every time I connect to the Internet I have a different IP.) How can I use NAT and do I need any kind of hardware?

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First, there are three ranges of private addresses specified by RFC 1918 that are handed out if you are behind some type of firewall, proxy, etc.

Second, I am going to assume that you are trying to use Internet Connection Sharing (ICS). Even if your upstream provider is using a private address, ICS should still work. ICS allows you to connect your LAN to the Internet through your ISP. All that is needed is that the server be powered-up, that is connected to the modem, and that your client machines are configured to use DHCP.

Generally, the steps to configure ICS are as follows

  1. Log onto the Server as administrator or you need to be a member of the administrators group.
  2. Open Network and Dialup Connections
  3. Click on the sharing tab
  4. Verify the ICS check box is selected
  5. Click on the Applications tab if you wish to configure any specific applications
  6. Configure the clients

After ICS is configured your users should be able to e-mail, FTP, or use Explorer just as if they were already connected to the ISP.

There are several good sites that detail this setup step-by-step. Surf over to for step-by-step screen shots.

This was first published in April 2003

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