Windows 2000 and ICS

Microsoft made a huge number of changes to their Desktop systems with the advent of Windows 2000 with nowhere the least of them made in the networking department. Still not perfect by any means, but a major step forward from the Win9x days, IMHO. One important improvement that Win2k has over Win9x is that you no longer have to reboot the PC when you change the IP address, but the improvements made to ICS over Win98SE/ME are astounding compared to that small feat! Essentially, if you install two Network Adapters in a Windows 2000 machine, Windows will allow one of them to be used for sharing it's network connection with the other adapter then being pre-set to connect to an private network. Easy.

System Requirements

An Internet service on a gateway machine can be processor intensive, depending both on the Gateway and Clients users' Internet Usage. This is probably more of an issue on a Windows machine than a Linux machine due to the fact that you need to have the WIndows environment up within Windows in order to use the sharing capabilities, whereas with Linux this is not normally necessary. As Windows requires Windows to be running (!), there is a great temptation to use the ICS machine as a workstation as well, but this can cause serious performance issues when clients want to use the ICS machines services. At minimum, I recommend at least a 300Mhz system with at least 128MB of RAM. If, for whatever reason, you need to use the ICS machine as a workstation as well, then I'd suggest doubling both of those.

Like most Internet Gateways, a Windows 2000 machine requires that it has two ethernet adapters installed, at least one of which must have a 10BaseT interface and connect to the Cable Modem using a straight RJ45 cable. The other adapter should connect to your internal network by whatever method used by the private LAN, be it RJ45, Thin/Thicknet or whatever. The information contained here uses 10baseT connectivity throughout. Like ALL gateways, it must also be switched in order for any LAN clients to be able to contact the outside world. If you do not want this situation then the only alternative is to purchase an all-in-one Gateway/Router/Firewall such as a Linksys or SMC Barricade (see the page on routers;-)).

As far as TCP/IP settings for the ICS machine, the CM attached NIC should have it's address DNS server set to be obtained automatically. The other NIC will be set, by ICS, to, so there is no need to configure anything for this. Note tho' that if you already have an address configured on NIC2 then this will be overridden when the other NIC is enabled as shared.

Clients that wish to use the ICS server need to have their TCP/IP properties set to automatic also. ICS will enable both a DHCP and a DNS service that the clients can use these to obtain their address, gateway and DNS server. Logically, the setup will look like that depicted in the following diag:

Win2K Network Diagram

Enabling Sharing

As previously stated, adding two NICs to a Windows 2000 machine adds the facility for one of them to be a shared device that other machines on a private network can also use. Consider a Windows 200o machine that contains two Local Area connections, shown as 5 and 7 in the following screen dump. Connection 5 is connected to the Local LAN and 7 is connected to the Cable Modem, which is the interface on which sharing will be enabled.

Network Places

Selecting the properties for Connection 7 reveals the adapter and protocol settings. All protocols except TCP/IP should be unticked on this interface, as shown below. Notice that two tabs are available in the Properties. The Sharing tab is added automatically by Windows when two network interfaces are present.

Win2K TCP/IP Properties

The properties for TCP/IP need to be set for DHCP (or, 'Obtain an IP address automatically' is ticked). In addition, DNS server addresses will also need to be set as automatic. This ensures that your ICS machine will get it's IP settings from NTL's DHCP server.

Win2k TCP/IP Properties

Selecting the Sharing tab reveals a single option - Enable Internet Connection Sharing for this connection.

Win2K NIC Share Properties

When ICS is enabled, Windows prompts a warning about changing the local LAN IP address to Comfirm that you want sharing enabled on the interface, and setup is complete!

Win2K Address Warning

The TCP/IP properties for the local LAN are reset to that shown below. No changes should be made to these properties, lest ICS is disrupted.

Win2K ICS Client TCP/IP Properties

Client TCP/IP Setup

Enabling ICs automatically sets your network to use as it's network number. The hosts on your network must also use this network number as part of their IP address, with the host part being a number between 2 and 254 (1 cannot be used as the ICS machine already has that address!). ICS does provide a DHCP server, so the simplest method for getting the client PCs to connect is to set them for automatic address and DNS servers. This will result in the client PCs having both default gateway and DNS server as

In some instances, DHCP does not work particularly well with ICS and it may be necessary to configure the client machines manually. In this case, the client needs to have the following settings:

  1. IP address is specified as with a mask of
  2. The Gateway Address is set to
  3. DNS Servers are set to and (these are NTL's DNS servers)

Subsequent machines added to the Network will also require identical settings, bar the assigned IP Address which will require the final digit to be unique. For example, addresses, and are all valid addresses that can be used. I would avoid using addresses in the range to in order to avoid any address conflicts in the event the Windows DHCP server allocates an IP address that has already been set manually on a different machine.

© Nig's Net Written using the Bluefish HTML Editor on RedHat 9.0.

All Copyrights and Trademarks ACK'd. Not to do so would be a SYN!