Firewall

NixOS includes an integrated firewall based on iptables/nftables, which can be configured declaratively through the NixOS system configuration. By default, the firewall is enabled and restricts incoming network connections, allowing users to explicitly define which ports and services should be accessible.

Enable

The firewall is enabled by default on NixOS. To explicitly ensure it is enabled, add the following option to your system configuration:

❄︎ /etc/nixos/configuration.nix

  networking.firewall.enable = true;

With the firewall enabled, all local ports and services will be unreachable from external connections unless explicitly allowed.

To use the newer nftables backend instead of iptables, set the option networking.nftables.enable to true.

Configuration

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

❄︎ /etc/nixos/configuration.nix

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

Refer to networking.firewall for more firewall module options.

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

⚠︎

Warning: Firewall rules may be overwritten by Docker, as per https://github.com/NixOS/nixpkgs/issues/111852

Interface specific rules

It is possible to define firewall rules for specific network interfaces. This can be useful for allowing different ports or services on different network connections. Add the following to your system configuration:

❄︎ /etc/nixos/configuration.nix

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

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

Tips and tricks

Temporary firewall rules

If using iptables, for temporary changes to the firewall rules, you can install the nixos-firewall-tool package, which is a thin wrapper around iptables.