From Computer Networking: A Top-Down Approach, Fifth Edition; Chapter 2; problem P19
P19. In this problem, we use the useful tool dig tool available on Unix and Linux hosts to explore the hierarchy of DNS servers. Recall that in Figure 2.21, a DNS server higher in the DNS hierarchy delegates a DNS query to a DNS server lower in the hierarchy, by sending back to the DNS client the name of that lower-level DNS server. First read the man page for dig, and then answer the following questions.
a. Starting with a root DNS server (from one of the root servers [a-m].root-servers.net), initiate a sequence of queries for the IP address for your department's Web server by using dig. Show the list of the names of DNS servers in the delegation chain in answering your query.
b. Repeat part a) for several popular Web sites, such as google.com, yahoo.com, or amazon.com.