nixos-config/modules/system/devices/networking/ips/default.nix

{ config, lib, ... }:
{
  options.ips = lib.mkOption {
    type = lib.types.attrs;
  };

  config.ips = rec {
    localSpan = "10.1.0";
    server = "10.2.0.1";
    pc = "10.2.0.100";
    vm = "10.2.0.101";
    hx = "10.2.0.150";
  };
}