In this problem, we use the useful tool dig tool available on Unix and Linux hos

Question

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].rootservers.
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.

Explanation / Answer

The format to invoke dig is

dig @<name.of.dns.server> <record-type><domain-name>

where,

Let us consider the root server A.ROOT-SERVERS.NET

As we need to know the IP address, we use the type ‘A’.

For example, if we perform the dig on the website google.com, the command to be used is:

dig A.ROOT-SERVERS.NET A google.com

It provides the required output.

The list of the names of DNS servers in the delegation chain for this query are

ns1.google.com

ns4.google.com

ns2.google.com

ns.3google.com

Similarly, if the command is used for yahoo.com, the format is

dig A.ROOT-SERVERS.NET A yahoo.com

and the name servers are

ns3.yahoo.com

ns2.yahoo.com

ns4.yahoo.com

ns8.yahoo.com

ns1.yahoo.com

ns5.yahoo.com

ns6.yahoo.com

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