Based off https://gist.github.com/LeamHall/5a4917cb31fbc1e67996

dns-tester.rb

require 'socket'

ARGF.each do |line|
  if /^\s*(\S+)\s+((?:\d{1,3}\.){3}\d{1,3})(?!\d)/ =~ line
    host = $1
    listed_ip = $2

    begin
      addrinfo = Socket::getaddrinfo(host, nil, :INET)
      returned_ips = addrinfo.map {|a| a[3]}
      puts "#{host}: Listed #{listed_ip} Returned IPs #{returned_ips.join ", "}."
    rescue SocketError => e
      $stderr.puts "Oops: #{e} for: #{host} #{listed_ip}"
    end
  else
    $stderr.puts "Ignoring #{line}"
  end
end