manatee: Add home-assistant module

hosts/manatee/modules/network/default.nix

@@ -3,6 +3,10 @@
   networking = {
     hostName = "manatee";
 
+    # Required for asymmetric routing (sending replies out a different interface
+    # than the default route). Without this, the kernel drops the return traffic.
+    firewall.checkReversePath = "loose";
+
     defaultGateway = "192.168.50.1";
     nameservers = [ "1.1.1.1" ];
     interfaces = {
@@ -16,7 +20,25 @@
             }
           ];
         };
+
+        ipv4.routes = [
+          {
+            address = "0.0.0.0";
+            prefixLength = 0;
+            via = "192.168.50.1"; # Router
+            options = {
+              table = "100";
+            };
+          }
+        ];
       };
     };
+
+    # Route packets from machines local IP back to router
+    localCommands = ''
+      # Add the rule only if it doesn't exist yet (idempotent)
+      ip rule list | grep -q "from 192.168.50.203 lookup 100" || \
+      ip rule add from 192.168.50.203 lookup 100 priority 5000
+    '';
   };
 }