Linux: Firewalling - Testing

Contents

•  Testing

• 0.04 [2001-06-05]: Last update before going public

Testing of firewall configuration

If you have need for a commercial auditing, then look e.g. at http://www.aerasec.de/security/services/, they offer different kind of.

Local test using netstat

• Open TCP ports:
• netstat -lnpt
• Open UDP ports:
• netstat -lnpu

Local and remote test using nmap

• See manpage and information on the Internet for details
• For the search for open TCP ports use:
• nmap -sS -P0 -p 1-65535 localhost
• For the search for open UDP ports use:
• nmap -sU -P0 -p 1-65535 localhost
• For the search for static packet filter for DNS and active FTP use:
• nmap -sS -P0 -p 1-65535 -g 20 localhost
• If you detect open ports, you have no chance for changes other than forbid active FTP
• nmap -sS -P0 -p 1-65535 -g 53 localhost
• If you detect open ports, you have a misconfigured port filter setup
• nmap -sU -P0 -p 1-65535 -g 53 localhost
• If you detect open ports, you have no chance for changes other than setup specific destination IPv4 addresses for DNS queries, e.g. the same you use as forwarder or in the resolver configuration

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