Firewall

NixOS provides an interface to configure the Nftables based firewall through the option networking.firewall.

Enable

To enable the firewall, simply put following code into your system configuration

/etc/nixos/configuration.nix

networking.firewall.enable = true;

This will make all local ports and services unreachable from external connections.

Configuration

To allow specific TCP/UDP ports or port ranges on all interfaces, you can use following syntax:

networking.firewall = {
  enable = true;
  allowedTCPPorts = [ 80 443 ];
  allowedUDPPortRanges = [
    { from = 4000; to = 4007; }
    { from = 8000; to = 8010; }
  ];
};

Note: Many services also provide an option to open required firewall ports automatically. For example, the media server Jellyfin offers the option services.jellyfin.openFirewall = true; which will open required TCP ports.

Interface specific firewall rules can be applied like this

networking.firewall.interfaces."eth0".allowedTCPPorts = [ 80 443 ];

In this case, ports 80 and 443 will be allowed for the interface eth0.