15.4.8 Lab - Observe DNS Resolution-done
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Metropolitan Community College, Omaha *
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Feb 20, 2024
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Lab - Observe DNS Resolution
Objectives
Part 1: Observe the DNS Conversion of a URL to an IP Address
Part 2: Observe DNS Lookup Using the nslookup Command on a Web Site
Part 3: Observe DNS Lookup Using the nslookup Command on Mail Servers
Background / Scenario
The 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 used. Common protocols are Hypertext Transfer Protocol (HTTP), Hypertext Transfer Protocol over Secure Socket Layer (HTTPS), and File Transfer Protocol (FTP).
DNS uses the second part of the URL, which in this example is www.cisco.com. DNS translates the domain name (www.cisco.com) to an IP address to allow the source host to reach the destination server. In this lab, you will observe DNS in action and use the nslookup
(name server lookup) command to obtain additional DNS information. Required Resources
1 PC (Windows with internet and command prompt access)
Part 1: Observe the DNS Conversion of a URL to an IP Address
a.
Open a Windows command prompt.
Open a Windows command prompt.
b.
At the command prompt, ping the URL for the Internet Corporation for Assigned Names and Numbers (ICANN) at www.icann.org
. ICANN coordinates the DNS, IP addresses, top-level domain name system management, and root server system management functions. The computer must translate www.icann.org into an IP address to know where to send the Internet Control Message Protocol (ICMP) packets.
The first line of the output displays www.icann.org
converted to an IP address by DNS. You should be able to see the effect of DNS, even if your institution has a firewall that prevents pinging, or if the destination server has prevented you from pinging its web server.
Note
: If the domain name is resolved to an IPv6 address, use the command ping -4 www.icann.org
to translate into an IPv4 address if desired.
Record the IP addresses for www.icann.org.
192.0.32.7
Close the Windows command prompt
c.
Type the IPv4 addresses from step b into a web browser, instead of the URL. Enter https://192.0.32.7 in the web browser. If your computer has an IPv6 address you can enter the IPv6 address. https://[2620:0:2d0:200::7]
in the web browser.
d.
Notice that the ICANN home web page is displayed without using DNS.
Most humans find it easier to remember words, rather than numbers. If you tell someone to go to www.icann.org
, they can probably remember that. If you told them to go to 192.0.32.7, they would have a difficult time remembering an IP address. Computers process in numbers. DNS is the process of translating words into numbers. Additionally, there is a second translation that takes place. Humans think in Base 10 numbers. Computers process in Base 2 numbers. The Base 10 IP address 192.0.32.7 in Base
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Lab - Observe DNS Resolution
2 numbers is 11000000.00000000.00100000.00000111. What happens if you cut and paste these Base 2
numbers into a browser? It doesn`t work because the browser doesn`t recognize base 2.
e.
At a command prompt, ping www.cisco.com
.
Note
: If the domain name is resolved to an IPv6 address, use the command ping -4 www.cisco.com
to translate into an IPv4 address if desired.
Open a windows command prompt
C:\> ping www.cisco.com
C:\> ping -4 www.cisco.com
Questions:
When you ping www.cisco.com, do you get the same IP address as the example? Explain.
NO, because cisco`s web content supposed to be hosted on a series of mirror servers.
Type the IP address that you obtained when you pinged www.cisco.com into a browser. Does the web site display? Explain.
NO, because probably the web server is not configured to accept ip addresses sent from a browser.
Close the windows command prompt
Part 2: Observe DNS Lookup Using the nslookup Command on a Web Site
a.
At the command prompt, type the nslookup command. Your result will be different than the example.
Open a windows command prompt
C:\> nslookup
Question:
What is the default DNS server used? Fixed line ISP
Type your answers here.
b.
Notice how the command prompt changed to a greater than (>) symbol. This is the nslookup
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.
c.
At the nslookup prompt, type www.cisco.com
.
> www.cisco.com
Default Server: one.one.one.one
Address: 1.1.1.1
Non-authoritative answer:
Name: e2867.dsca.akamaiedge.net
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Lab - Observe DNS Resolution
Addresses: 2600:1404:a:395::b33
2600:1404:a:38e:::b33
172.230.155.162
Aliases: www.cisco.com
www.cisco.com.akadns.net
wwwds.cisco.com.edgekey.net
wwwds.cisco.com.edgekey.net.globalredir.akadns.net
Questions:
What is the translated IPv4 address?
23.198.34.155
Note
: The IP address from your location will most likely be different because Cisco uses mirrored servers in various locations around the world.
Is it the same as the IP address shown with the ping
command?
yes
here.
Under addresses, in addition to the 172.230.155.162 IP address, there are the following numbers: 2600:1404:a:395::b33 and 2600:1404:a:38e:::b33. What are these?
IPV6 ADDRESS THROUGH WHICH IT IS POSSIBLE TO REACH THE WEBSITE. d.
At the nslookup 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.
> 172.230.155.162
Default Server: one.one.one.one
Address: 1.1.1.1
Name: a172-230-155-162.deploy.static.akamaitechnologies.com
Address: 172.230.155.162
You can use the nslookup
tool to translate domain names into IP addresses. You can also use it to translate IP addresses into domain names.
Question:
Using the nslookup
tool, record the IP addresses associated with www.google.com
.
2607:f8b0:4009:817::2004
and 142.250.190.4
Part 3: Observe DNS Lookup Using the nslookup Command on Mail Servers
a.
At the nslookup prompt, type set type=mx to use nslookup
to identify mail servers.
> set type=mx
b.
At the nslookup prompt, type cisco.com
.
> cisco.com
Server: one.one.one.one
Address: 1.1.1.1
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Lab - Observe DNS Resolution
Non-authoritative answer:
cisco.com MX preference = 20, mail exchanger = rcdn-mx-01.cisco.com
cisco.com MX preference = 30, mail exchanger = aer-mx-01.cisco.com
cisco.com MX preference = 10, mail exchanger = alln-mx-01.cisco.com
A fundamental principle of network design is redundancy (more than one mail server is configured). In this
way, if one of the mail servers is unreachable, then the computer making the query tries the second mail server. Email administrators determine which mail server is contacted first by using MX preference
. The mail server with the lowest MX preference
is contacted first. Based upon the output above, which mail server will be contacted first when the email is sent to cisco.com?
rcdn-mx-01.cisco.com
answers here
.
c.
At the nslookup prompt, type exit
to return to the regular PC command prompt.
d.
At the PC command prompt, type ipconfig /all
.
Question:
Write the IP addresses of all the DNS servers that your school uses.
68.105.28.11
68.105.29.11
68.105.28.12
here.
Close the windows command prompt
Reflection Question
What is the fundamental purpose of DNS?
It translates letters to number. For example, ipv4 o ipv6
.
re.
End of document
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