# File lib/simp/cli/config/utils.rb, line 43
    def validate_netmask( x )
      # a brute-force regexp that validates all possible valid netmasks
      nums = '(128|192|224|240|248|252|254)'
      znums = '(0|128|192|224|240|248|252|254)'
      regex = /^((#{nums}\.0\.0\.0)|(255\.#{znums}\.0\.0)|(255\.255\.#{znums}\.0)|(255\.255\.255\.#{znums})|(255\.255\.255\.255))$/i
      x =~ regex ? true: false
    end