Make computer as a router

I'm doing my final year project now. For that I need to connect two different network through a router. But in my college there was no router. But I can have as many computers I need to work. So I planned to make a computer as a router. Here I used Ubuntu, a debian based linux destro to make the system to route.

First I have connected two NIC (Network Interface Card) to a computer. And I had a default NIC. That totally three NICs I had in my computer. So I can connect three different network segments together. Now connect three network segments with the computer and assign IP address for three NICs. Now enable IP forwarding in the Ubuntu machine. Restart networking. Thats all the system became router.

I just gave the outline. Now I'm going to tell what I have done in my college. I have four systems totally. One of them is added two more NICs. That system(Ub) is installed Ubuntu 10.10. And the other three have been installed with Windows XP operating system (Xp1,Xp2,Xp3). I decided three XP systems as separate network segments. I have assigned the following IP for those machines

• Xp1 - 192.168.1.105
• Xp2 - 10.10.3.101
• Xp3 - 10.10.2.101

And for those three NICs in the Ubuntu system as follows

• eth0 - 192.168.1.100
• eth1 - 10.10.3.100
• eth2 - 10.10.2.100

I don't have any switch or router as I have told already. So I connected systems directly. But to connect two computers, the cable should be cross connected (search in Internet for cross cable). And I have connected the systems as follows

• Xp1 - Ub eth0
• Xp2 - Ub eth1
• Xp3 - Ub eth2

In the Ubuntu machine I given the IP address in GUI mode. But it didn't worked for me. I don't know why. So I have assigned the IP directly in the interfaces (/etc/network/interfaces) as above. And restarted the network using the following comment

• $ /etc/init.d/networking stop
• $ service networking start

Alas! I made my computer into router. Now you can ping any system from any other system.