Configuring the firewall with UFW

What UFW is

UFW (Uncomplicated Firewall) is a simplified front end on top of the native Linux firewall (iptables/nftables). It lets you define easily which ports accept incoming connections, without handling the more complex iptables syntax directly.

Installing UFW

On Debian/Ubuntu, UFW is usually already present. If it is not:

sudo apt install ufw

The basic rule before enabling it

sudo ufw allow 22/tcp

(Replace 22 with your actual SSH port if you changed it.)

Enabling the firewall

sudo ufw enable

A confirmation is requested, because this command can cut an active connection if the SSH rule has not been added beforehand.

Opening other common ports

sudo ufw allow 80/tcp     # HTTP
sudo ufw allow 443/tcp    # HTTPS
sudo ufw allow 25565/tcp  # example: Minecraft server

Checking the active rules

sudo ufw status verbose

Shows the full list of active rules along with their state (allowed, denied).

Removing a rule

sudo ufw delete allow 80/tcp

Disabling it temporarily

sudo ufw disable

Useful for a one-off diagnosis (working out whether a connection problem comes from the firewall or elsewhere); re-enable it afterwards with sudo ufw enable.