Run nslookup to determine the authoritative dns

2. Run nslookup to determine the authoritative DNS servers for a university in
Europe.
3. Run nslookup so that one of the DNS servers obtained in Question 2 is queried for
the mail servers for Yahoo! mail. What is its IP address?
2. ipconfig
ipconfig (for Windows) and ifconfig (for Linux/Unix) are among the most useful little
utilities in your host, especially for debugging network issues. Here we’ll only describe
ipconfig , although the Linux/Unix ifconfig is very similar. ipconfig can be used to show
your current TCP/IP information, including your address, DNS server addresses, adapter
type and so on. For example, if you all this information about your host simply by
entering
ipconfig \all
into the Command Prompt, as shown in the following screenshot.

ipconfig is also very useful for managing the DNS information stored in your host. In
Section 2.5 we learned that a host can cache DNS records it recently obtained. To see
these cached records, after the prompt C:\> provide the following command:
ipconfig /displaydns
Each entry shows the remaining Time to Live (TTL) in seconds. To clear the cache, enter
ipconfig /flushdns
Flushing the DNS cache clears all entries and reloads the entries from the hosts file.

3. Tracing DNS with Wireshark
Now that we are familiar with nslookup and ipconfig , we’re ready to get down to some
serious business. Let’s first capture the DNS packets that are generated by ordinary Web-
surfing activity.
 Use ipconfig to empty the DNS cache in your host.
 Open your browser and empty your browser cache. (With Internet Explorer,
go to Tools menu and select Internet Options; then in the General tab select
Delete Files.)
 Open Wireshark and enter “ip.addr == your_IP_address” into the filter, where
you obtain your_IP_address with ipconfig. This filter removes all packets that
neither originate nor are destined to your host.
 Start packet capture in Wireshark.
 With your browser, visit the Web page:
 Stop packet capture.
If you are unable to run Wireshark on a live network connection, you can download a
packet trace file that was captured while following the steps above on one of the author’s
computers 2 . Answer the following questions. Whenever possible, when answering a
question below, you should hand in a printout of the packet(s) within the trace that you
used to answer the question asked. Annotate the printout 3 to explain your answer. To
print a packet, use File->Print , choose Selected packet only , choose Packet summary
line, and select the minimum amount of packet detail that you need to answer the
question.
2 Download the zip file and extract the file dns-
ethereal-trace-1. The traces in this zip file were collected by Wireshark running on one of the author’s
computers, while performing the steps indicated in the Wireshark lab. Once you have downloaded the trace,