I have a usb modem with internet connection. And I need to share its connection to my PC Desktop. So, here is my experiment howto share internet connection via ppp0.
My laptop is using Ubuntu 11.04 with 2 connections: ppp0 and Eth0. My PC Desktop is connected to my laptop using cross-cable with Eth0. I use static IP address for both Eth0.
To share ppp0 connection, I just need install ‘firestarter’ in my laptop.
~$ sudo apt-get install firestarter
Then configure ‘firestarter’ to select the device which connected to internet and enabled the internet connection sharing.