Distributed Systems Lab: Network Connections and DNS



We now come to the second part where we query the Domain Name System using the 
   dig
command. Find out how it works using man pages (on Linux or on the Web). An explanation of the output produced by dig can be found in Connected: An Internet Encyclopedia.

1. Mail Exchange Servers

Find the mail exchange servers of unibz.it.

2. Root Servers

Find all root servers.

3. Domain Servers

Which are the name servers for the it domain?

4. Authoritative Answers

Find the IP address of www.mit.edu. Is the answer authoritative?
Is the answer authoritative? (Hint: Check the flags in the header and find out what they mean, looking into RFC1035.)
Contact a name server that will give you an authoritative answer.

5. Default Servers

Which are the domain names of the name servers used by default when dig (or nslookup or any other resolver) is called?
Hint: look into /etc/resolv.conf.

6. Duplicate Hosts

How many hosts can be reached under www.google.com?
Explain what you find.

7. Time to Live

What is the time to live of the records?
How does the time to live change when you call dig repeatedly? Why is this the case?

8. Caching

Let your default name server do some caching: ask for a the name of a rarely used machine (e.g., the ftp server of some university in some other country).
Check how long the lookup takes the first and the second time. Are the answers authoritative?
Can a non-authoritative DNS server return authoritative answers?

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