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1、Computer netowrks Labs1Computer netowrks LabsDNS, Data Encapsulation and Frame ExaminationDNS, Data Encapsulation and Frame ExaminationLearning ObjectivesAt completion of this lab, you will be able to:1. Use Wireshark to capture and analyze DNS message2. Understand how DNS works3. use nslookup and i
2、pconfig commands 4. Explain the header fields in an Ethernet II frame.5. understand data encapsulationComputer netowrks Labs26. Report and Feedback on this labAnswer all questions with supporting screenshots. Please fill in the following feedback form and append it to the report. Your feedback is va
3、luable to us so that we can improve this lab, and make the course welcome.For each task, please rate the following in the scale of 1 through 5: The degree of difficulty: 1 = too easy; 5 = too difficult The learning experience: 1 = learned nothing; 5 = learned a lot Your interest: 1 = no interest; 5=
4、 high interest Time used for the task: in minutes Task Difficulty (15) Learning (15) Interest (15) Time ( min)Task 0Task 1Task 2Task 3Task 4Your suggestion/comment:BackgroundWhen upper layer protocols communicate with each other, data at the sending host flows down the TCP/IP protocol layers and is
5、encapsulated into a protocol data unit at lower layer, and finally encapsulated in a Layer 2 frame. For example, DNS message is often transported by UDP protocol on layer 4. So DNS message at the sending host is encapsulated in a UDP segment; the UDP segment is then encapsulated in an IP packet, and
6、 the IP packet is encapsulated finally in a layer 2 frame. The frame composition is dependent on the media access type, or the network. For example, if the media access is Ethernet, then the Layer 2 frame encapsulation will be Ethernet II. When learning about data encapsulation and protocol operatio
7、ns, it is helpful to analyze the header information found in the protocol data units. The DNS protocol operation, ipconfig command, and Ethernet II frame header will be examined in this lab. Ethernet II frames can support various upper layer protocols.For more background information, please read the
8、 lectures 02, 04-05, 10, 11. Computer netowrks Labs3TasksTask 0 Protocol Layers and Data EncapsulationAs we have discussed in Lecture 02, Internet is inter-connected networks based on TCP/IP protocols. Read the slides or textbook to learn how data goes through protocol layers and how data is encapsu
9、lated in the protocol data units. There are conventional names for the protocol data units for different layer protocols.Question 1. What are names for the protocol data units (PDUs) for layer 4, layer 3, and layer 2 protocols in TCP/IP reference model by filling the follow form:name for PDU of laye
10、r 4 protocols: segment name for PDU of layer 3 protocol: packet name for PDU of layer 2 protocol: frame Task 1 DNS and nslookupAs we discussed, IP address is used to identify a host uniquely on the Internet. But IP address is not user-friendly and that is why domain name was introduced. The Domain N
11、ame System (DNS) translates host names to IP addresses, providing a critical role in the Internet infrastructure. In this task, we practice the nslookup tool, which is available both in Linux/Unix and MS Windows. To run nslookup in MS Windows, you need to open the command line window by starting the
12、 command cmd.exe. With nslookup, you can query any specified DNS server (by default, your local configured DNS server) for a DNS record. 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.Type the c
13、ommand nslookup www.MIT.edu, and capture the output, as I did and showed below:Computer netowrks Labs4Question 2: What is the DNS server IP address that is used to query and find IP address for www.MIT.edu? And IP address for www.MIT.edu ?Type the command “nslookup -type=NS ”, and capture the output
14、, as I did and showed below:Question 3: What are domain name servers for and their IP addresses?Type the command “nslookup ”, and capture the output, as I did and showed below:Question 4: Which DNS server is used to query and for name resolution?You can also use nslookup to find the mapping from I
15、P addresses to the host names. Type the commands “nslookup 192.168.156.101” and “nslookup ”, and capture the output, as I did and showed below:Computer netowrks Labs5Question 5: Can a host have multiple host names? What is the IP address for moodle.tec.hkr.se? How many names do you find for this IP address? Task 2 DNS and ipconfigipconfig (for Windows) and ifconfig (for Linux/Unix, interface configuration) are among the most useful tools for debugging network issues. ipconfig can be used to show your current TCP/IP information, including your address, DNS
