Can a simple firewall be designed from standard computer equipment? What hardware components would you need for a proxy server?
A firewall determines who gets access to a network and who doesn't. There are two types of firewalls, hardware firewalls and software firewalls.
A typical hardware firewall intercepts and inspects network traffic using packet filtering. As messages come in from the network, the firewall examines the header of the TCP/IP packet to determine the source and destination addresses. It then compares this information against a set of predefined or user-created rules that determine whether the packet is to be forwarded or dropped. A hardware firewall doesn't have to be a dedicated device. Most residential routers sold today have firewalls built in.
A software firewall offers protection from outside attempts to control or gain access to a computer. Many software firewalls also offer user-defined controls for setting up safe file and printer sharing, as well as safeguards to block unsafe applications from running on the system. A good software firewall runs in the background and uses only a small amount of system resources.
The benefit of software firewalls over hardware firewalls is that software firewalls are able to protect an individual machine by knowing which programs are running, and by monitoring potentially dangerous applications, such as e-mail and Web browsing not just what it transmits in packets.
The major downside to a software firewall is that it only protects one computer, the machine the software is installed on, not an entire network. So to protect a network of machines with software firewalls, the software firewall must be installed and configured on each system. Maintaining individual software firewalls on networks with many PCs can be a time-consuming process.
To create a hardware firewall, you can use a standard computer with special software designed for the purpose. One such example is by using an old computer and the open-source software called SmoothWall Express. SmoothWall Express uses a special implementation of Linux to turn a PC into a dedicated hardware firewall. SmoothWall software prevents any unauthorised data to pass through the firewall and is invisible to the outside world.
Smoothwall also contains Web Proxy software called Squid. The minimum requirements for a computer to run Smoothwall is as follows:
- Processor: Any Pentium-compatible processor. Must be 150 MHz or faster.
- Memory: At least 32 MB of RAM, but ideally 64 MB or more. With less than 64 MB of RAM, it may not be possible to run all services, especially the Web Proxy Server and the Intrusion Detection System.
- Hard Disk: An IDE drive of 2 GB capacity is recommended.
- CD-ROM: An IDE CD-ROM drive is recommended for ease of installation.
- Video Card, Monitor, Keyboard: Any. Required only for initial installation; all subsequent administration is carried out remotely over the network.
- Network Card: At least one supported network card is needed to connect the SmoothWall Express to the protected local network.
- ADSL Modem: various models.
McDonough, A. 1997. ChannelWeb. Build This Cheap But Effective Firewall. Retrieved on July 12, 2009, from http://www.crn.com/white-box/197000873;jsessionid=FYVQ2LJZS4MEOQSNDLOSKH0CJUNN2JVN?pgno=2
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