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How to protect your computer with a firewall

The door to safety swings on the hinges of common sense

A firewall is a program that acts as a protective barrier, a gatekeeper or a security guard between you and the Internet. In other words, it prevents unauthorized Internet traffic from entering or leaving your computer, both by software programs and users.

The best free firewalls are:

  1. ZoneAlarm Free Firewall is one of the world’s most downloaded amd popular firewall software programs. It is a limited version of ZoneAlarm Pro/ZoneAlarm Pro Antivirus & Firewall, which provide only a firewall for free. ZoneAlarm Free Firewall

    ZoneAlarm Free Firewall

  2. Comodo Firewall Free is a personal firewall software.
  3. GNU/Linux Firewall: Firewalld and ufw.

macOS’s Firewall

To turn on the Firewall: System Preferences, Security & Privacy, Firewall. Click Turn On Firewall, then click Firewall Options to fine-tune the firewall settings, Enable Automatically allow built-in/downloaded signed software to receive incoming connections (it adds stock apps -iTunes, Mail, Messages- and downloaded apps that are signed by a valid certificate authority to be automatically added to the list of allowed apps) and stealth mode (it prevents your macOS from responding to probing requests or queries to reveal its existence from the network).

Firewalld

Firewalld is a firewall that uses nftables by default. This brief tutorial shows you how to install and configure it in Arch, GNU/Linux.

# Install necessary packages
sudo pacman -S firewalld ipset ebtables
# Enable and start firewalld.service.
sudo systemctl enable --now firewalld.service
# Change the default zone to home.
sudo firewall-cmd --set-default-zone=home
# Open ftp, htpp, samba, and synchthing services: --permanent because changes made in Runtime configuration are lost when the firewalld service is restarted.
sudo firewall-cmd --add-service=ftp --permanent
sudo firewall-cmd --add-service=http --permanent
sudo firewall-cmd --add-service=samba --permanent
sudo firewall-cmd --zone=home --add-service=syncthing --permanent
# Allow traffic on an incoming port (24800) -Barrier-
sudo firewall-cmd --add-port=24800/tcp --permanent
# Restart the firewall.
sudo firewall-cmd --reload
# List allowed service and ports on the system
❯ sudo firewall-cmd --list-service
dhcpv6-client fttp http mdns samba samba-client ssh syncthing

Ufw

Ufw stands for the uncomplicated firewall

  1. Installation: sudo apt install ufw
  2. Basic usage. Enable/Disable ufw: sudo ufw enable/disable
  3. Reload ufw: sudo ufw reload
  4. Check the current sate of UFW. If it is active, it shows a list of rules: sudo ufw status verbose
  5. Allow ssh (sudo ufw allow ssh/tcp), Barrier (sudo ufw allow 24800), NFS (sudo ufw allow from [client IP address or local network] to any port nfs).
  6. Allow Synching: sudo ufw allow synching synching-gui
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