Should my class methods have access to my class variables?

NameError: uninitialized class variable @@file_type in NetworkAssetFile::NetworkAssetBase
        from /home/jontec/public_html/dvd2/app/helpers/network_asset_file.rb:94:in `lookup'
        from /home/jontec/public_html/dvd2/app/helpers/network_asset_file.rb:86:in `each'
        from /home/jontec/public_html/dvd2/app/helpers/network_asset_file.rb:86:in `lookup'
        from /home/jontec/public_html/dvd2/app/models/network_asset_extensions.rb:3:in `find'
        from (irb):1

## network_asset_file.rb [ruby]
module NetworkAssetFile
  module NetworkAssetBase
    # this module is used to extend my NetworkAsset classes
    def lookup
      ...
      if @@file_type
        search_regex << "\\.#{ @@file_type }"
      else
        search_regex << '\.\w+'
      end
      ...
    end
  end
end

## network_function_file.rb [ruby]
class NetworkFunctionFile
  extend NetworkAssetFile::NetworkAssetBase # added as class methods
  ...
  @@file_type = "txt"
  ...
end