3 Tracing DNS with Wireshark Now that we are familiar with nslookup and

3 tracing dns with wireshark now that we are familiar

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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 Websurfing 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 (the IP address for the computer on which you are running Wireshark) 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. 4
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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’scomputers1. Answer the following questions:4.(6 points) Locate the DNS query and response messages. Are they sent over UDP or TCP?5.(10 points) What is the destination port for the DNS query message? What is the source port of DNS response message?6.(10 points) To what IP address is the DNS query message sent? Use ipconfig determine the IP address of your local DNS server. Are these two IP addresses the same?7.(8 points) Examine the DNS query message. What “Type” of DNS query is it? Does the query message contain any “answers”?8.(8 points) Examine the DNS response message. How many “answers” are provided? What does each of these answers contain?9.(10 points) Consider the subsequent TCP SYN packet sent by your host. Does the destination IP address of the SYN packet correspond to any of the IP addresses provided in the DNS response message?10. (10 points) This web page contains images. Before retrieving each image, does your hostissue new DNS queries?11. (Up to 10 points) What is the most significant thing you learned from this lab and why is it important? to What to Turn In Print out and turn in a paper copy of your lab work on the due date at the beginning of class. It should include the answers to 11 questions. Please use complete sentences. 5
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  • Winter '12
  • MichaelChu
  • IP address, Domain Name System, Nslookup, local DNS server

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