Utility Classes In Ruby on Rails

To use new, the thing your calling it on must be a class, not a module. You're using a module. Change module to class in lib/utilities/network_utility.rb.

Lib or Classes

Little utility classes like this typically go in the lib folder, though some people prefer to create a folder called classes. Whichever you choose, make sure you import the folder in config/application.rb, as the lib folder is not autoloaded:

config.autoload_paths += %W(#{config.root}/lib)

Concerns

If instead of a utility class, you want to extend some of your models with reusable code, you may also wish to look at the new Rails 4 concerns folders which encourage you to extract reusable modules:

see: How to use concerns in Rails 4