box1.nix

  virtualisation = {
    memorySize = 512;
    graphics = false;
    qemu.networkingOptions = [ "-net nic,macaddr=52:54:00:12:34:01" "-net vde,sock=/run/vde.ctl" ];
  };

box2.nix

  virtualisation = {
    memorySize = 512;
    graphics = false;
    qemu.networkingOptions = [ "-net nic,macaddr=52:54:00:12:34:02" "-net vde,sock=/run/vde.ctl" ];
  };

router.nix

  virtualisation = {
    memorySize = 1024;
    qemu.networkingOptions = [
      "-net nic,vlan=0,macaddr=52:54:00:12:34:00"
      "-net vde,vlan=0,sock=/run/vde.ctl"
    ];
  };