Module to detect whether an IP address is rfc1918 or not (private class A, B, C + loopback)

rfc1918.rb

# From https://gist.github.com/bmc/2728451
module RFC1918
  def self.is_unroutable(ip)
    if ! (ip =~ /^(\d{1,3}).(\d{1,3}).(\d{1,3}).(\d{1,3})$/)
      raise "#{ip} is not an IP address"
    end

    octets = [$1, $2, $3, $4].map &:to_i
    raise "#{ip} is a bad IP address" unless octets.all? {|o| o < 256}

    # The Internet Assigned Numbers Authority (IANA) has reserved the
    # following three blocks of the IP address space for private internets:
    #
    #   10.0.0.0        -   10.255.255.255  (10/8 prefix)
    #   172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
    #   192.168.0.0     -   192.168.255.255 (192.168/16 prefix)

    (octets[0] == 10) ||
    ((octets[0] == 172) && (octets[1] >= 16) && (octets[1] <= 31)) ||
    ((octets[0] == 192) && (octets[1] == 168)) ||
    (octets[0] == 127)
  end
end