5.3.1.3 Lab – Observing DNS Name Resolution Answers

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5.3.1.3 Lab – Observing DNS Name Resolution Answers

Lab – Observing DNS Name Resolution (Answers Version)

Answers Note: Red font color or gray highlights indicate text that appears in the Answers copy only.

Objectives

  • Observe the conversion of a URL to an IP address.
  • Observe DNS lookup using the nslookup command.

Background / Scenario

Domain Name System (DNS) is invoked when you type a Uniform Resource Locator (URL), such as http://www.cisco.com, into a web browser. The first part of the URL describes which protocol is being used. Common protocols are HTTP (Hypertext Transfer Protocol), HTTPS (Hypertext Transfer Protocol over Secure Socket Layer), and FTP (File Transfer Protocol).

DNS uses the second part of the URL, which in this example is www.cisco.com. DNS translates the domain name (like www.cisco.com) to an IP address to allow the source host to reach the destination host.

Work in pairs to complete this lab.

Required Resources

  • 1 PC (Windows 10) with Internet connectivity

Step 1: Observe DNS conversion.

  1. Right-click Start and select Command Prompt.
  2. At the command prompt, type ping cisco.com and press enter. The computer needs to translate cisco.com into an IP address so it knows where to send the Internet Control Message Protocol (ICMP) packets. Ping is a type of ICMP packet.
  3. The first line of the output shows cisco.com converted to an IP address by DNS. You should be able to see the effect of DNS even if your school has a firewall that prevents pinging, or if Cisco has prevented people from pinging their web server.Which IP address is shown on the screen?_______________________
    72.163.4.161
    Is it the same as the one shown in the figure?_____________________
    Answers may vary.
    Should cisco.com always resolve to the same IP address? Explain.
    ____________________________________________________________________________________
    It does not always resolve to the same IP address because there are multiple public IP addresses that resolve to cisco.com.
  4. Work together with another student and discuss one or two other application (besides the ping command) in which the computer would need to use DNS to translate a domain name to an IP address.
    ____________________________________________________________________________________
    A web browser, FTP client, or email client.

Step 2: Verify DNS operation using the nslookup command.

  1. At the command prompt, type the nslookup command and press enter.The image above shows that the Default DNS Server was configured to use a Google DNS server. What is your Default Server listed as? __________________________________________________________
    Answers may vary.
  2. After issuing the previous nslookup command, notice how the command prompt changed to a single >. This is the nslookup program’s prompt. From this prompt, you can enter commands related to DNS.
    At the prompt, type ? to see a list of all the available commands that you can use in nslookup mode.
    List three commands that you can use with nslookup:
    ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
    set type=x to set the query type, server <NAME> to set the default DNS server, and help to get command help
  3. At the nslookup prompt, type cisco.com.
    What is the translated IP address?_____________________
    2001:420:1101:1::a and 72.163.4.161
    Is the IP address an IPv4 address or an IPv6 address?_______________
    Both IPv4 and IPv6.
    Is it the same as the IP address shown with the ping command?____________
    Yes.
    At the prompt, type the IP address of the Cisco web server that you just found. What is the Name result?____________________________________________________________________________________
    www1.cisco.com

Step 3: Identify mail servers using the nslookup command

  1. To identify mail servers using nslookup, type set type=mx..
  2. At the prompt, enter cisco.com.What are the names of the Cisco mail servers identified in the mail exchanger field?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
    aer-mx-01.cisco.com, alln-mx-01.cisco.com, rcdn-mx-01.cisco.com.
  3. At the prompt, type exit to return to the regular command prompt.
  4. At the prompt, type ipconfig /all.
  5. Write the IP addresses of all the DNS servers that your school computer uses.
    ____________________________________________________________________________________
    Answers will vary.
  6. Type exit and press enter to close the command prompt window.

Reflection

  1. If your school did not have a DNS server, what effect would this have on your use of the Internet?_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
    You would not be able to browse the web or use any network application that relies on name to IP address translation.
  2. Some companies do not dedicate a single server for DNS. Instead, the DNS server provides other functions as well. Which functions do you think might be included on a DNS server? Use the ipconfig /all command to help you with this.
    _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
    Email, printer, and file-share name translations. Active Directory domain controller function.