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+# Firewall {#sec-firewall}
+
+NixOS has a simple stateful firewall that blocks incoming connections
+and other unexpected packets. The firewall applies to both IPv4 and IPv6
+traffic. It is enabled by default. It can be disabled as follows:
+
+```nix
+networking.firewall.enable = false;
+```
+
+If the firewall is enabled, you can open specific TCP ports to the
+outside world:
+
+```nix
+networking.firewall.allowedTCPPorts = [ 80 443 ];
+```
+
+Note that TCP port 22 (ssh) is opened automatically if the SSH daemon is
+enabled (`services.openssh.enable = true`). UDP ports can be opened through
+[](#opt-networking.firewall.allowedUDPPorts).
+
+To open ranges of TCP ports:
+
+```nix
+networking.firewall.allowedTCPPortRanges = [
+  { from = 4000; to = 4007; }
+  { from = 8000; to = 8010; }
+];
+```
+
+Similarly, UDP port ranges can be opened through
+[](#opt-networking.firewall.allowedUDPPortRanges).