Can a Raspberry PI be used as a firewall?

Can a Raspberry PI be used as a firewall? This question comes back often. Well, I have tested it. The test conditions are:

• a Raspberry PI Model B (256MB of RAM)
• a USB to Ethernet wired interface. 100 Mbits/sec.
• Raspian (May 2015) as the OS.
• My Internet connection is 30 Mbits/sec. for download, 10 Mbits/sec. for the upload speed.
• www.speedtest.net has been used to carry the speed tests.

The answer is NO. I got a download speed of about 30 MBits/sec. Using a PC as the firewall with a similar setup, I achieved around 32 MBits/sec. While doing the download test, the CPU usage was 100% while being 20% for the upload test. Memory was not an issue with about 165 MB free.

I would certainly use this Raspberry PI as a firewall for an Internet connection of 20-20 Mbits/sec. or less.

A similar test will soon be performed using a Raspberry PI 2.