add ip and mac arithmatic functions

calculate vm mac addresses

nixos/default.nix

@@ -94,5 +94,9 @@
       minicom
       socat
     ];
+
+    nixpkgs.overlays = [
+      (final: prev: { lib = prev.lib // (import ./net.nix prev); })
+    ];
   };
 }

nixos/machines/default.nix

@@ -64,7 +64,7 @@
 
     nixosModule = { pkgs, ... }: {
       # TODO: would be cool to create a check that a mac address is only ever assigned to one VM.
-      lab.vm.macAddress = "BA:DB:EE:F0:00:00";
+      lab.vm.id = 0;
 
       programs.bash.interactiveShellInit = ''
         echo "Hello world from inside a virtual machine!!" | ${pkgs.lolcat}/bin/lolcat
@@ -81,7 +81,7 @@
         networking.dmz.services.enable = true;
 
         vm = {
-          macAddress = "BA:DB:EE:F0:00:07";
+          id = 7;
           staticNetworking = true;
           staticIPv4 = config.lab.networking.dmz.ipv4.services;
           staticIPv6 = config.lab.networking.dmz.ipv6.services;

nixos/virtual.nix

@@ -1,9 +1,17 @@
-{ lib, config, hypervisorConfig, ... }: {
+{ pkgs, lib, config, hypervisorConfig, ... }: {
   options.lab.vm = {
-    macAddress = lib.mkOption {
+    baseMACAddress = lib.mkOption {
+      default = "BA:DB:EE:F0:00:00";
       type = lib.types.str;
       description = ''
-        The MAC address of the VM's main NIC.
+        Base MAC address for VMs in the DMZ.
+      '';
+    };
+
+    id = lib.mkOption {
+      type = lib.types.int;
+      description = ''
+        Unique identifier of this VM from wich the MAC address is derived.
       '';
     };
 
@@ -45,7 +53,7 @@
       interfaces = [{
         type = "tap";
         id = "vm-${config.networking.hostName}";
-        mac = config.lab.vm.macAddress;
+        mac = pkgs.lib.net.mac.add config.lab.vm.id config.lab.vm.baseMACAddress;
       }];
     };