How to Turn an Old Computer Into a Firewall

by Nathaniel Bloom

A dedicated firewall increases the security of your home or office network. Many hardware and software firewalls are available; however, these firewalls tend to lack flexibility when setting advanced firewall rules and decision-making rule sets. Using an old computer as a firewall for your network gives you access to these advanced functions. Turn an old computer into a firewall by using freely-available operating systems and software.


Install a second network interface card onto the computer's motherboard using any available PCI slot. The computer will now have two network interfaces, counting the original network adapter that's integrated into the motherboard.


Boot the computer using a freely-available Linux operating system disc like Ubuntu, Fedora or CentOS (see Resources). The installation process will ask you for setup data and customization options. Each operating system has its own unique setup procedure; however, most of them will ask you a fairly standardized set of questions.


Install the operating system by following the installation script's prompts and performing any tasks that the installation procedure asks for. If the system asks you which type of installation you'd like, choose "Server" or "Firewall"; do not choose "Desktop" or "Workstation." Choose a graphical user interface such as Gnome or KDE for the installation.


Configure one of the computer's network cards with a static IP address that resides on your local network. This will be your computer's local network interface. Configure the other network card to use DHCP for the IP address configuration. This will be your public network interface. You can usually set this up during the installation; if not, set these options in the network interface admin tools after installation. You can usually find these tools by click the "System" menu and choosing "Administration."


Configure the operating system's firewall after starting it up. Configure the firewall's rule chains or tables to address the fact that you have two network cards, and that one is local and the other is public. Set the default rule for incoming connections on the public interface to "DROP."


Connect the public network card to your modem or router with an Ethernet cable. Connect the other card to your local area network or other device. The old computer is now a firewall between the Internet and your network.


  • check Virtually any Linux distribution out will work for this procedure.


  • close If your old computer contains any data that you want to keep, back it up before beginning.

Items you will need

About the Author

Nathaniel Bloom is a veteran in the computer support field, working with some of the major companies in the information technology industry. In 1997 he began writing technical documentation and articles for high-technology businesses, and eHow and kb.norsetech websites. His education includes professional certifications in various technologies in addition to decades of constant, in-depth involvement in real-world computer user needs.

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Photo Credits

  • photo_camera Computer Network Interface Card image by Northwest Photo from