P19. In this problem, we use the useful dig tool available on Unix and Linux hos

Question

P19. In this problem, we use the useful 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.

Explanation / Answer

a Ans:)
Below are DNS servers in the delegation chain

1.a.root-servers.net
2.E.GTLD-SERVERS.NET
3.ns1.umass.edu(authoritative)

1.The first (a.root-servers.net) Command is dig +norecurse
@a.root-servers.net any gaia.cs.umass.edu

AUTHORITY SECTION ARE:

1.edu. 172800 IN NS E.GTLD-SERVERS.NET.
2.edu. 172800 IN NS A.GTLD-SERVERS.NET.
3.edu. 172800 IN NS G3.NSTLD.COM.
4.edu. 172800 IN NS D.GTLD-SERVERS.NET.
5.edu. 172800 IN NS H3.NSTLD.COM.
6.edu. 172800 IN NS L3.NSTLD.COM.
7.edu. 172800 IN NS M3.NSTLD.COM.
8.edu. 172800 IN NS C.GTLD-SERVERS.NET.

2.The (ns1.umass.edu(authoritative)) DNS servers command is
dig +norecurse @ns1.umass.edu any gaia.cs.umass.edu

1.gaia.cs.umass.edu. 21600 IN A 128.119.245.12

3.The (E.GTLD-SERVERS.NET) DNS servers command
dig +norecurse @E.GTLD-SERVERS.NET any gaia.cs.umass.edu

1.umass.edu. 172800 IN NS ns1.umass.edu.
2.umass.edu. 172800 IN NS ns2.umass.edu.
3.umass.edu. 172800 IN NS ns3.umass.edu.

bAns:)

Below are the several popular Web sites:

1.a.root-servers.net
2.E.GTLD-SERVERS.NET
3.ns1.umass.edu

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