A guide to Internet Connection Sharing using MS Windows

ICS stands for Internet Connection Sharing. This is a software that in included in all version of Windows starting from MS Window 98SE. ICS allows the MS Windows PC to

act as a gateway to the Internet. ICS software consist of a router, a NAT (Network

Address Translator), DNS and a DHCP server. The router will route your internal network to the external network (the Internet). The NAT provides address translation so that you only need 1 IP address for your entire home LAN (Local Area Network). The DNS provides name lookups. The DHCP server assigns IP addresses to the computers in your home LAN.

A typical home LAN consist of several computers. In the diagram below, the home LAN consist of 2 Atari (Atari#1 and Atari #2) and a Wintel PC. The Wintel PC is the ICS PC, and it has 2 network interface - one to connect to the ISP (in green) and the other to connect to your home LAN (in red).

A network request from the Atari computer will flow to the ISP/Internet via the ICS PC. The returning response from Internet flows back to the Atari computer, again via the ICS PC. In this configuration the ICS PC must always be on and connected to the ISP in order for the Atari computer to access Internet.

Setting up ICS in windows

IP address assignment on the Atari

The ISP will assign a IP address to your Wintel PC for the interface that is connect to the Internet. This IP address is different from the IP address that you gives you Atari computer.

In the ICS configuration, the home LAN is defaulted to the private address IP subnet of 192.168.0.xxx where xxx is from 1 to 254. Being a private IP address range, no computer on the Internet will have this addresses. The ICS PC home LAN interface (that's the network card connected to the home LAN) will obtain an IP address of 192.168.0.1. This is by default and the recommendation is not to change this. The rest of the computers in the home LAN can take on any IP address number from 192.168.0.2 to 192.168.0.254.

This setup is for STING TCP/IP stack. Using Mintnet or MagiXnet TCP/IP stack will require different setup. However, the values of configurations (IP address, DNS and gateway) are the same for all TCP/IP stacks. Install STING on the Atari computer and

ROUTE.TAB file setup - the default gateway

One last thing to do is to set the route table file. The route will be to direct all traffic not destine for the home LAN out to the router. In this case the router will be the default gateway (ICS PC). The below route line is added to the last line of the ROUTE.TAB file

0.0.0.0 0.0.0.0 Ethernet0 192.168.0.1

Testing the setup

Reboot all the computers to make sure that everything starts up correctly. On the Atari computer perform these tests

• 1. Ping your local host (127.0.0.1) and IP address (192.168.0.228 - in this example).

  2. Ping the default gateway - 192.168.0.1

  3. Ping the ISP assigned IP address for you ICS computer (this is your external IP address).

  4. Ping the ISP DNS server.

If any of them fail, check the configuration of the ICS PC, making sure that the network interface is correctly defined and that the ICS software is enabled.

When all is well and you can ping all the hosts, fire up CAB. Reconfigure it to use a proxy server if required by your ISP. This proxy server information is easily obtainable from their website or you can check the ICS PC Internet Explorer configuration.