Firewall, easy to set up.

# apt-get install firehol
# nano /etc/default/firehol
(You'll find that there's text in this file: "START_FIREHOL=NO", change it to: "START_FIREHOL=YES". Exit nano saving changes.) 
# firehol-wizard 

You may have to press Enter once or twice to confirm that the wizard has detected everything right, but that's about it. 

Edit:

Sometimes firewall spits its log messages to the console, which can be very annoying if you want to do something outside X. If you use FireHOL, you can fix this by installing the "ulogd" package (apt-get install ulogd) and adding the line

code:

FIREHOL_LOG_MODE="ULOG"




to /etc/default/firehol. Then you can reboot and now all firewall log messages go to /var/log/ulog/syslogemu.log (instead of cluttering the console and system log messages). 

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post from Dead Parrot at Linuxquestions.org