To test your firewall there are a few software tools and a few online services to help you.

I suggest the following tools (of course you need two computers to run the test):

- Nessus is probably the best open source security scanner available.
  Nessus not only checks the firewall of a host, but also scans for known application vulnerabilities.
  I highly recommend Nessus for periodic (weekly, monthly, etc) scans.
- Nmap ("Network Mapper") is an open source utility for network exploration or security auditing.

There are a number of sites that offer firewall testing services to everyone:

- AuditMyPC
- BroadBand Reports port scanner.
- Security Space, a commercial service with a free scan.
  These people are using something like Nessus (if not Nessus itself).
- Shields UP!! NanoProbe Technology Internet Security Testing for... Windows Users. (note: well, it says for Windows, but it is a port scanner with a limited range of ports to be scanned...)
- SyGate Online Services (S.O.S.) Very nice site to quickly check the security of your system. They have a stealth scanner that tries to break the firewall with a few nice ways (this can show you the difference between FireHOL and a hand made stateless firewall).

Other testers on the net:

- Smurf Amplifier Registry (SAR) The SAR is a tool for Internet administrators being attacked by or implicated in smurf attacks, or those who wish to take precautions.

Other useful links:

- Top 50 Security Tools for UNIX

| $Id: fwtest.html,v 1.11 2013/01/07 00:10:31 ktsaou Exp $ FireHOL, a firewall for humans... © Copyright 2004 Costa Tsaousis <costa@tsaousis.gr>