hostnames.rb

#!/usr/bin/env ruby

require 'socket'

def random_hostnames
  loop do
    begin
      octets = Array.new(4) { rand(255) }
      hostname = Socket.gethostbyaddr(octets.pack('C4')).first
      puts "IP: #{octets.join('.')} -> Hostname: #{hostname}"
    rescue SocketError
      next
    end
  end
end

random_hostnames