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UFW is the default firewall configuration tool on Ubuntu and is simple to install on Debian.
Getting Started: https://www.howtoforge.com/tutorial/ufw-uncomplicated-firewall-on-ubuntu-15-04/
HowTo: https://www.digitalocean.com/community/tutorials/how-to-setup-a-firewall-with-ufw-on-an-ubuntu-and-debian-cloud-server