Use pbb policy routing module

modules/policyrouting/default.nix

@@ -0,0 +1,50 @@
+{ config, lib, ... }:
+
+with lib;
+
+let
+  cfg = config.petabyte.policyrouting;
+
+  ruleOpts = { ... }: {
+    options = {
+      prio = mkOption {
+        type = types.int;
+      };
+      rule = mkOption {
+        type = types.str;
+      };
+    };
+  };
+
+in {
+  options = {
+    petabyte.policyrouting = {
+      enable = mkEnableOption "Declarative Policy-Routing";
+      rules = mkOption {
+        type = with types; listOf (submodule ruleOpts);
+        default = [];
+      };
+      rules6 = mkOption {
+        type = with types; listOf (submodule ruleOpts);
+        default = [];
+      };
+      rules4 = mkOption {
+        type = with types; listOf (submodule ruleOpts);
+        default = [];
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    petabyte.policyrouting.rules = [
+      { rule = "lookup main"; prio = 32000; }
+    ];
+    networking.localCommands = ''
+      set -x
+      ip -6 rule flush
+      ip -4 rule flush
+      ${concatMapStringsSep "\n" ({ prio, rule }: "ip -6 rule add ${rule} prio ${toString prio}") (cfg.rules ++ cfg.rules6)}
+      ${concatMapStringsSep "\n" ({ prio, rule }: "ip -4 rule add ${rule} prio ${toString prio}") (cfg.rules ++ cfg.rules4)}
+    '';
+  };
+}