WiresharkLab_DNS.pdf - Wireshark Lab \u2013 DNS Domain Name System(DNS translates hostnames to IP addresses fulfilling a critical role in the Internet

WiresharkLab_DNS.pdf - Wireshark Lab u2013 DNS Domain Name...

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Wireshark Lab – DNS 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. 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. 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. It is the 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. 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. Consider the first command: nslookup In words, this command is saying “please send me the IP address for the host ;. The response from this command provides two pieces of information: (1) the name and IP address of the DNS server that provides the answer; and (2) the answer itself, which is the host name and IP address of . Although the response came from the local DNS server, it is quite possible that this local DNS server iteratively contacted several other DNS servers to get the answer. Now consider the second command: nslookup type=NS mit.edu In this example, we have provide d the option “ - type=NS” and the domain “mit.edu”. This causes nslookup to send a query for a type- NS record to the default local DNS server. In words, the query is saying, “please
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