iptables
========
https://www.raspberrypi.org/documentation/configuration/security.md
https://help.ubuntu.com/community/IptablesHowTo#Solution_.231_-_.2BAC8-etc.2BAC8-network.2BAC8-interfaces





(s.a. Sicherheit.txt)



ufw (Uncomplicated Firewall (UFW))
===
https://www.linux.com/learn/introduction-uncomplicated-firewall-ufw
simpler front end for iptables