Internet Connection Sharing (ICS)

Internet Connection Sharing (ICS) is a feature in Windows 2000 very similar to the same feature found in the second edition of Windows 98. With ICS, you can share a remote network connection from one machine with other machines on your single-subnet network. Essentially, ICS configures your Windows 2000 system as a Network Address Translation (NAT) server, translating private internal IP addresses to the public IP address provided by your ISP. Although this technology is usually used for sharing a Internet connection, it could also be used to share a connection to a private network. ICS is set up from the Sharing tab of the properties of a connection object.

A few important notes on ICS:

  • Ensure that the connection that is shared is the external connection (this would be your modem connection, or your second NIC connected to your DSL or Cable provider). You internal connection will automatically be reconfigured to support the range of addresses handed out by ICS.
  • Only an administrator can set up ICS.
  • You must have at least 2 connections on the system for it to work (for example, 1 NIC and a dial-up connection to your ISP)
  • ICS turns your machine into a mini-DHCP server, and will hand out addresses to your internal clients (who should be set to use DHCP).
  • You should not use ICS on a network containing existing DHCP servers (ICS does this), DNS servers (ICS proxies DNS requests), Windows 2000 domain controllers, or gateways (the gateway provided by ICS DHCP will be the ICS system internal interface). If you have these and need to continue using them, you will need to look at a server solution, such as NAT, found in Windows 2000 server Routing and Remote Access (RRAS).
  • ICS is simply a home and small office single-subnet connection sharing solution.

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.