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Configuring ICS on Windows XP

This is a step by step setup of how you get Windows XP to use Internet Connection Sharing or ICS.

These instructions assume that when you have a Cable Modem connection or an ADSL connection (frankly, it can also be a simple Dial-Up modem connection, but that won’t get you anywhere, would it?).

Let’s say you have the following LAN configuration:

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 Internet       |       |       |       | 212.143.143.12     (Real IP from ISP)    PRO1                  (This will be the ICS computer) 192.168.0.1    (Bogus IP – Configured by ICS)       |       |       |       | Switching Hub———PRO2       |                   192.168.0.2  (Bogus IP – Configured by ICS)       |       |       |       | 192.168.0.3    (Bogus IP – Configured by ICS)    PRO3

Instead of a hub you could use a crossover cable to the other computer but then you will only be able to connect 2 computers, and if you’d want more you’d need more NICs.

Step 1: Configure Internet Connection Sharing

  1. Right click "My Network Places" and select "Properties".

  2. In this window you should see an icon for "Local Area Connection" and "Local Area Connection 2" for both of your NIC’s.

  3. Right click on the Network Area Connection icon that connects to your Cable or ADSL modem, and select "Properties" from the drop down window.

If you’re using a modem to connect to the Internet (just like in the previous screenshot) you must right click the icon that represents the connection to the Internet.

  1. Click on the Advanced tab.

  1. Check the box next to "Allow other network users to connect through this computer’s Internet connection" and press "OK" to share your connection through this NIC.

  2. You will receive a warning window saying that your NIC will automatically receive an IP address of 192.168.0.1, and that if you have other computers on your LAN that have static IP addresses – you should configure them to obtain it automatically – otherwise you will probably break the connection with them.

  1. Acknowledge this warning.

  2. Back at the "My Network Places" Window, right click on your "Local Area Connection 2" icon and select Properties from the drop down menu.

  1. Check the TCP/IP settings by double clicking on the "Internet Protocol (TCP/IP)" line, or highlight it and then click the "Properties" button beneath it.

  1. You should make sure that your TCP/IP properties looks exactly like this.

These settings are auto configured by the ICS service.

Step 2: Configure network computers to use ICS

To get your Client computers up and working you must configure them to obtain an IP address automatically. To do so you must go to their Local Area Connection icons (like you did in step 1) and select the properties for the TCP/IP protocol. You must then select "Obtain IP address automatically" and press Ok.

To see if the computer has successfully received an IP address from the ICS service, go to a command prompt and type "ipconfig /all" (without the quotes you moron!). Notice that it should say "DHCP Enabled = Yes", and that the IP address should be in the 192.168.0.0 range (probably 192.168.0.2, 3, 4 and so on). If it’s not showing yet, you can force a renewal of the IP address by typing "ipconfig /renew" and waiting a few seconds.

If you’re using Win9X go to Start/Run and type "winipcfg" and do a renew from the window.

Problems

ICS is a practical feature for people that do not know how to configure their Internet Connection Sharing through NAT. But one thing should be clear as crystal:

ICS is CRAP!!! ICS is a no-no on operational networks!

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Remember:

  • ICS might ruin your network! If you have computers that are configured with static IP addresses you must now configure them to get their IP addresses automatically, and if you do not do so, they might not be able to communicate with you anymore (or create IP address conflicts).

  • ICS will cause your computer to behave as a DHCP server, and by doing so it will stop the regular DHCP service (if you ever had one running)!

  • ICS will act as a DNS proxy, and will render your existing DNS infrastructure useless (if you ever had one)!!!

  • ICS will ruin your Active Directory (no DNS? No AD!) unless it’s run on the Domain Controller itself, but that’s something you don’t want to do, do you?

  • ICS will not let you choose what IP address range to lease to it’s clients. It will only lease the 192.168.0.0 network range, and you cannot change that.

  • ICS has very limited port mapping functionality and low performance compared to the regular NAT service.

  • ICS is only good for 2-5 computer networks that do NOT have running DNS, AD, DHCP, Web or E-Mail services, and if that’s not the case – consider NAT.

With that said, carefully consider your situation and act accordingly.

Links

Configuring ICS on Windows 2000, XP, 98 and ME – In Hebrew

Configure Internet Connection Sharing in Windows XP – 306126

Troubleshooting Internet Connection Sharing in Windows XP – 308006

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