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Internet connection sharing

How to set up ICS in a branch office for cheap Internet connections.


Internet connection sharing
James Michael Stewart

Internet Connection Sharing or ICS is the service found on Windows 98, 98 SE, Me, 2000, XP, and .NET that allows a single Internet (or other network connection) to be shared with a small network. If you have branch offices with small office networks, ICS is an inexpensive way to take full advantage of cheap broadband access.

If you have DSL, ISDN, cable, or even satellite Internet access, your service is typically configured to allow only a single system to communicate over that link. With ICS, you can easily share that underused link with multiple computers.

The basics of ICS are fairly basic. First, you need the Internet connection. It can be a modem, an ISDN card, or a NIC connecting to a DSL or cable router/modem. Second, you need a separate NIC for your local network connection. In most cases, you'll be using twisted pair cabling and thus will need a hub to connect your network together. Every other system which will be added to the network also needs a NIC.

The way ICS works is basically it transforms your primary system (i.e. the one with the Internet connection) into a TCP/IP router. In addition to this, it also adds DNS forwarding and basic DHCP services to the primary system. It is very important not to attempt to use ICS on a network where an existing DNS server or DHCP server is present. Also, do not install (in the case of Windows 98, SE, or Me) or enable (in the case of Windows 2000, XP, or .NET) ICS on more than one system on the same network. Doing so will cause problems.

The documentation for ICS states that once enabled, the external interface on the primary system (i.e. the one connected to the Internet) will be assigned an IP address by your ISP (which can be statically assigned or dynamically assigned upon connection). However, the internal interface will be assigned the private IP address of The documentation goes on to state that all of the clients that will use ICS to gain Internet access will need to be configured to obtain their IP address configuration dynamically (i.e. by using DHCP). However, I have found that this is not the case, and you can statically assign IP addresses to the other clients.

If you do statically assign IP addresses to the ICS clients, you must be sure that you don't accidentally assign the same IP address to multiple machines. Second, you must define the same subnet mask and gateway on each system -- namely and respectively.

Depending on the performance capabilities of the primary system and the speed of the Internet connection you can easily use ICS to grant 2 to 20 local clients Internet access over your network.

James Michael Stewart is a researcher/writer at Lanwrights, Inc.

This was last published in January 2002

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