Lab03-DNS.pdf - Wireshark Lab DNS v6.02 Supplement to Computer Networking A Top-Down Approach 6th ed J.F Kurose and K.W Ross Tell me and I forget Show

Lab03-DNS.pdf - Wireshark Lab DNS v6.02 Supplement to...

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Wireshark Lab: DNS v6.02 Supplement to Computer Networking: A Top-Down Approach, 6 th ed., J.F. Kurose and K.W. Ross “Tell me and I forget. Show me and I remember. Involve me and I understand.” Chinese proverb © 2005 -21012, J.F Kurose and K.W. Ross, All Rights Reserved As described in Section 2.5 of the text 1 , the Domain Name System (DNS) translates hostnames to IP addresses, fulfilling a critical role in the Internet infrastructure. In this lab, we’ll take a closer look at the client side of DNS. Recall that the client’s role in the DNS is relatively simple a client sends a query to its local DNS server, and receives a response back. As shown in Figures 2.21 and 2.22 in the textbook, much can go on “under the covers,” invisible to the DNS clients, as the hierarchical DNS servers communicate with each other to either recursively or iteratively resolve the client’s DNS query. From the DNS client’s standpoint, however, the protocol is quite simple – a query is formulated to the local DNS server and a response is received from that server. Before beginning thi s lab, you’ll probably want to review DNS by reading Section 2.5 of the text. In particular, you may want to review the material on local DNS servers , DNS caching , DNS records and messages , and the TYPE field in the DNS record. 1. nslookup In this lab , we’ll make extensive use of the nslookup tool, which is available in most Linux/Unix and Microsoft platforms today. To run nslookup in Linux/Unix, you just type the nslookup command on the command line. To run it in Windows, open the Command Prompt and run nslookup on the command line. In it is most basic operation, nslookup tool allows the host running the tool to query any specified DNS server for a DNS record. The queried DNS server can be a root DNS server, a top-level-domain DNS server, an authoritative DNS server, or an intermediate DNS server (see the textbook for definitions of these terms). To accomplish this task, nslookup sends a DNS query to the specified DNS server, receives a DNS reply from that same DNS server, and displays the result. 1 References to figures and sections are for the 6 th edition of our text, Computer Networks, A Top-down Approach, 6 th ed., J.F. Kurose and K.W. Ross, Addison-Wesley/Pearson, 2012.
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The above screenshot shows the results of three independent nslookup commands (displayed in the Windows Command Prompt). In this example, the client host is located on the campus of Polytechnic University in Brooklyn, where the default local DNS server is dns-prime.poly.edu. When running nslookup , if no DNS server is specified, then nslookup sends the query to the default DNS server, which in this case is dns- prime.poly.edu. The below screenshot on the next page shows the results of those commands that displayed in Linux command line (located on Computer Engineering Department of Hacettepe University Beytepe Campus).
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