2.Run nslookupto determine the authoritative DNS servers for a university in Europe.3.Run nslookupso that one of the DNS servers obtained in Question 2 is queried forthe mail servers for Yahoo! mail. What is its IP address?2. ipconfigipconfig(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 ifconfigis very similar. ipconfigcan 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 \allinto the Command Prompt, as shown in the following screenshot.
ipconfigis 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 /displaydnsEach entry shows the remaining Time to Live (TTL) in seconds. To clear the cache, enteripconfig /flushdnsFlushing the DNS cache clears all entries and reloads the entries from the hosts file.
3. Tracing DNS with WiresharkNow that we are familiar with nslookupand 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 ipconfigto 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 computers2. 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 printout3to 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.2Download 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,