added defaultGateway

hosts/base/default.nix

@@ -10,7 +10,10 @@
 
   nixpkgs.config.allowUnfree = true;
 
-  nix.settings.experimental-features = [ "nix-command" "flakes" ];
+  nix.settings.experimental-features = [
+    "nix-command"
+    "flakes"
+  ];
 
   kropcloud = {
     admin = {

hosts/hydra/default.nix

@@ -5,6 +5,7 @@
       ipv4 = {
         address = "192.168.1.160";
         prefixLength = 24;
+        defaultGateway = "192.168.1.1";
       };
     };
   };

nixosModules/networking/default.nix

@@ -18,6 +18,12 @@ let
       default = null;
       example = if version == 4 then 24 else 64;
     };
+    defaultGateway = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      description = "The defautl gateway IPv${version}";
+      default = null;
+      example = if version == 4 then "192.168.1.1" else null;
+    };
   };
 in
 {
@@ -34,9 +40,10 @@ in
 
     assertions = [
       {
-        assertion = !(cfg.ipv4.address == null || cfg.ipv4.prefixLength == null);
+        assertion =
+          !(cfg.ipv4.address == null || cfg.ipv4.prefixLength == null || cfg.ipv4.defaultGateway == null);
         message = ''
-          You need to provide valid values for both `address` and `prefixLength` in `kropcloud.networking.ipv4`
+          You need to provide valid values for `address`, `prefixLength` and `defaultGateway` in `kropcloud.networking.ipv4`
           when either is set.
         '';
       }
@@ -57,8 +64,17 @@ in
           ];
         };
       };
-      useDHCP = (cfg.ipv4.address == null || cfg.ipv4.prefixLength == null);
-      nameservers = [ "8.8.8.8" "1.1.1.1" ];
+      useDHCP = (
+        cfg.ipv4.address == null || cfg.ipv4.prefixLength == null || cfg.ipv4.defaultGateway == null
+      );
+      defaultGateway = lib.mkIf (cfg.ipv4.defaultGateway != null) { address = cfg.ipv4.defaultGateway; };
+      nameservers =
+        lib.mkIf
+          (cfg.ipv4.address != null || cfg.ipv4.prefixLength != null || cfg.ipv4.defaultGateway != null)
+          [
+            "8.8.8.8"
+            "1.1.1.1"
+          ];
     };
   };
 }