Lab 6.2.1 Observing DNS Name Resolution

Lab 6.2.1 Observing DNS Name Resolution

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

Background / Preparation
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 ones 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 in order to allow the source host to reach the destination host.
Work in pairs to complete this lab.
The following resources are required:
• Windows-based computer with Internet connectivity
• Access to the Run command


Step 1: Observe DNS conversion
a. Click the Start button, select Run, type cmd, and then click OK. The command prompt window appears.
b. At the command prompt, type ping www.cisco.com. The computer needs to translate www.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.
c. The first line of the output shows www.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.


d. Which IP address is shown on the screen?
Jawaban:  68.254.168.178

e. Is it the same as the one shown in the figure? Why do you think this occurred?
f. Work together with another student and discuss one or two other instances (besides the ping command) in which the computer would use DNS.


Step 2: Verify DNS operation using the nslookup command
a. At the command prompt, type the nslookup command.
b. b. What is the default DNS server being used?
Jawaban : default DNS server yang digunaka yaitu ns4.unp.ac.id

c. Notice how the command prompt changed. This is the NSLOOKUP prompt. From this prompt, you can enter commands related to DNS.
d. At the prompt, type ? to see a list of all the available commands that you can use in NSLOOKUP mode.
e. Write three commands that you can use with NSLOOKUP.
 Jawaban :  name, help, root.

f. At the NSLOOKUP prompt, type www.cisco.com.
g. What is the translated IP address?
The answer : the translated IP address is 60.254.176.170
h. Is it the same as the IP address shown with the ping command?
The answer : No, I don’t think so.
i. At the prompt, type the IP address of the Cisco web server that you just found. You can use NSLOOKUP to get the domain name of an IP address if you do not know the URL. Using the previous procedures, find an IP address associated with www.google.com.
The answer :
There are some IP that associated with www.google.com sucah as 64.233.181.103, 64.233.181.147, 64.233.181.106, 64.233.181.99, 64.233.181.104 and 64.233.181.105

Step 3: Identify mail servers using the nslookup command
a. At the prompt, type set type=mx to have NSLOOKUP identify mail servers.
b. At the prompt, type www.cisco.com.
c. What is the primary name server, the responsible mail address, and the default Time to Live (TTL)?
The answer: No mail exchange (MX) records available for www.cisco.com
d. At the prompt, type exit to return to the regular command prompt.
e. At the prompt, type ipconfig /all.
f. Write the IP addresses of all the DNS servers that your school uses.
Jawaban 

DHCP Server . . . . . . . . . . . : 192.168.194.129
DNS Servers . . . . . . . . . . . : 192.168.194.129
10.1.1.5
202.134.0.155

g. Type exit to close the command prompt window.

Step 4: Reflection
a. If your school did not have a DNS server, what effect would this have on your use of the Internet?

b. 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.