We pick e.root-servers.net, one of the 13 root servers (1), and ask it about 216-239-53-81.google.com and learn that com is delegated to 13 name servers (2), so we ask m.gtld-servers.net where we learn that google.com is delegated to four name servers, including ns1.google.com (3), so we ask that one and get the following answer: