Don't throw that old PC away just yet, it still has some life in it yet. No matter how bad your old PC is it can always be used as a router, and your old router as a switch. All you need is two nic cards for it. Originally I did this on a Pentium 3 with 256 MBs of memory, 10GB HD. I had that setup for around 6 months before the hard disk finally died. Therefore I've looked around to a solution hard disk free and more secure... you can't install a rootkit on a read_only support!!

Iptables is a very dynamic tool to configure things with Linux box, like free Linux firewall and Linux router to share internet connection. So this notes is ’bout configuring Linux box as a secure and safe internet gateway using iptables.

I’m always comfortable with fedora core so I used a fedora based distro name NST - NetworkSecurityToolkit . That is a Linux livecd (based on Fedora Core 5) mainly devoted to the network security that means: it has all the necessary software gear to analyze and study the network.

Features:

use the NST live cd to bootup a safe and un-writable linux system and load from a read_only floppy all the gateway setup (20k bytes). The gateway is completely closed to prevent attacks, only two Masters PC in the dirty network could be admin that by ssh or https. The safe local network has a dhcp server to allow a "dynamic" network connection.