fwmon is a firewall monitor for Linux which integrates with ipchains to give you realtime notification of firewall events. It has fairly customizable output, allowing you to display a packet summary, hex, and ascii data dumps to stdout, a logfile, or tcpdump-style capture files. It also boasts some simple security features such as the ability to chroot itself, and does not need to run as root.
09f707cab121a67dc9422dc939f863acbd2bcc94a414d389b3be0603120b9fb7