Saturday, May 15, 2010

Changing ICS Sharing IP in Windows XP

ICS (Internet Connection Sharing) in Windows XP is quite useful in few occasions. Like if you have a laptop connected to a wired connection and you want to share your connection to other wireless devices, then it can be handy. Note that Windows XP works quite well as Wireless AP in adhoc mode.

There are cases where your wired connection IP range will be in 192.168.0.x, in this case ICS and adhoc sharing will not work, not at least without some tweaks.

To put this in perspective, here is my network.

[Cable Provider (network1)]--[Home Network (network2)]--[XP Machine with ICS (network3)]

My high speed internet connection from my cable company provides dynamic ip in the range 66.90.106/22, let me call this network1.

My second network (network2), is my home network. This is a wireless AP with wired capability. I was too lazy when I setup this network and used the default. So its network is 192.168.0/24. Well, this is the same network that ICS is using.

For my network3, of course using ICS, it is also 192.168.0/24 network. So this is where the issue starts.

There are various ways to fix this but I have two at hand. One option would be to change my wireless AP network address. Second option is to change ICS IP address.

Since I have some time today, I am exploring the ICS option.

To recap, ICS network are by default in the 192.168.0/24 form. Since this is used by my netowrk2, we will try to tweak this a little bit.

When we did the ICS, we shared it to an interface, let us call this "Local Area Connection". If you check "Local Area Connection", you will notice that it is assigned an IP address of 192.168.0.1. To get the devices connected to network3, we would change "Local Area Connection" to:

IP: 192.168.2.1 (or any private IP range)
Netmask: 255.255.255.0
Default Gateway : <blank>

Now, for devices connected to netowork3, we need to change IP manually to:

<device1>
IP: 192.168.2.10
Netmask: 255.255.255.0
Default Gateway: 192.168.2.1 <IP of "Local Area Connection">
Preferred DNS: 8.8.8.8 <Google Public DNS server>
Alternate DNS: 8.8.4.4 <Google Public DNS server>

That's it... your third network should now be able to connect to the internet. This solution is not perfect. In fact, I am having "Windows IP Conflict" every now and then which I am trying to chase down.

Update: (2010/05/15)
It seems like the Windows IP Conflict was caused by "AGN Filter Interface" or "AT&T Wi-Fi Support Driver".

~ts

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