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Wireshark Hands-on Assignment
Familiar with Wireshark User Interface
The startup screen of Wireshark looks like the following.
When Wireshark begins capturing packets, the screen looks like the following.
Network interfaces installed on this computer.
Yours may be different.
Filter toolbar
Packet List panel
Packet Details panel Packet Bytes panel
Wireshark Hands-on Assignment
The detailed functionality of the filter toolbar and each panel can be found on
http://www.wireshark.org/docs/wsug_html_chunked/ChapterUsing.html.
Problem 1: Capturing Web Browser HTTP Traffic (30 marks)
(1) Start your favorite web browser1
(2) From the Wireshark menu, select Capture è Interfaces…. A Wireshark: Capture Interfaces window
appears.
Select a network interface. If you have more than one network interfaces, select the one with non-zero
number of packets. Then click the [Start] button to start capturing packets. A packet window likes the
one shown in Familiar with Wireshark User Interface above appears.
(3) In your favorite web browser, open the following URL.
http://gaia.cs.umass.edu/networks/resources/index.html
(4) After your web browser displays the content of the above URL, stop Wireshark packet capture: from the
Wireshark menu, select Capture è Stop.
(5) In Wireshark Filter toolbar, enter http. Then click the Apply button.
Only HTTP messages are displayed in the Packet List panel.
(6) In the Packet List panel, look for the HTTP GET message2 from the Info column.
Select this message, the protocols and protocol fields of the packet selected are displayed in Packet
Details panel. In the Packet Details panel, click the + sign next to Transmission Control Protocol to show
the details of the TCP packet.
Questions
Based on the above results, answer the following questions.
1. What languages (if any) does your browser indicate that it can accept to the server in HTTP Get message?
(3 marks)
1 Clear your web browser’s cache to ensure you are loading the fresh version of web page from the Internet. Different
web browsers have different steps. Refer to http://www.wikihow.com/Clear-Your-Browser%27s-Cache if necessary. 2 Some web browser may use HTTP/1.0 instead of HTTP/1.1.
Wireshark Hands-on Assignment
4
2. What application layer protocol does your web browser access above website? (3 marks)
3. What transport layer protocol does this HTTP GET packet use? (3 marks)
4. What is the destination IP address and port of the HTTP GET message? (3 marks)
5. For the HTTP GET message, what is the next sequence number in the TCP header? (3 marks)
6. Find the response packet corresponding to the HTTP GET message. Take a screenshot. Briefly describe
how you are able to tell this packet corresponds to the HTTP GET message. (3 marks)
Do the following steps:
• Start up your web browser, and make sure your browser’s cache is cleared.
• Start the Wireshark sniffer.
• Enter the following URL into your browser http://gaia.cs.umass.edu/networks/cnrg_wireless-10-02.pdf
Your browser should display an one-page pdf file.
• Quickly enter the same URL into your browser again (or simply select the refresh button on your
browser)
• Stop Wireshark packet capture, and enter “http” in the display-filter-specification window, so that only
captured HTTP messages will be displayed later in the packet-listing window.
(Download problem 1.pcapng if you failed to capture the trace.)
Answer the following questions:
7. Inspect the contents of the first HTTP GET request from your browser to the server. Do you see an “IFMODIFIED-SINCE”
line in the HTTP GET? (1 mark)
8. Inspect the contents of the server response. Did the server explicitly return the contents of the file?
How can you tell? (4 marks)
9. Now inspect the contents of the second HTTP GET request that requests the pdf file. Do you see an “IFMODIFIED-SINCE:”
line in the HTTP GET? If so, what information follows the “IF-MODIFIED-SINCE:”
header? (3 marks)
10. What is the HTTP status code and phrase returned from the server in response to this second HTTP GET?
Did the server explicitly return the contents of the file? Explain. (4 marks)
Wireshark Hands-on Assignment
5
Problem 2: Capturing DNS Traffic (20 marks)
Background
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.
In it is 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 www.mit.edu
In words, this command is saying “please send me the IP address for the host www.mit.edu”. Try it yourself
(You may use a different host name that you like). 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 www.mit.edu. Although the response came from the default
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 provided 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 send
me the host names of the authoritative DNS for mit.edu”. (When the –type option is not used, nslookup uses
the default, which is to query for type A records.) The answer first indicates the DNS server that is providing
the answer (which is the default local DNS server) along with several MIT nameservers. Each of these servers
is indeed an authoritative DNS server for the hosts on the MIT campus. However, nslookup also indicates
that the answer is “non-authoritative,” meaning that this answer came from the cache of some server rather
than from an authoritative MIT DNS server. Finally, the answer also includes the IP addresses of the
authoritative DNS servers at MIT. (Even though the type-NS query generated by nslookup did not explicitly
ask for the IP addresses, the local DNS server returned these “for free” and nslookup displays the result.)
Now finally consider the third command:
nslookup www.google.com asia1.akam.net
In this example, we indicate that we want to the query sent to the DNS server asia1.akam.net rather than to
the default DNS server. Thus, the query and reply transaction takes place directly between our querying host
and asia1.akam.net. In this example, the DNS server asia1.akam.net provides the IP address of the host
www.google.com, which is a web server at the Google Inc..
Do the following steps:
Wireshark Hands-on Assignment
(1) Open Windows Command Prompt3
: è All Programs è Accessories è Command Prompt.
(2) From the Wireshark menu, select Capture è Interfaces…. A Wireshark: Capture Interfaces window
appears. Select a network interface then click the [Start] button to start capturing packets.
(3) In Windows Command Prompt, enter the following command4 to clear all cached DNS entries.
ipconfig /flushdns
(4) In Windows Command Prompt, enter the following command5
nslookup www.openrice.com
(-timeout=60: set the timeout to 60 seconds.)
The output should contain the IP address of https://www.openrice.com
(5) Stop Wireshark packet capture: from the Wireshark menu, select Capture è Stop.
(6) In Wireshark Filter toolbar, enter dns. Then click the Apply button.
Only DNS packets are displayed in the Packet List panel.
Questions
Based on the above results, answer the following questions.
1. Are they sent over UDP or TCP? (2 marks) How can you tell? (2 marks)
2. In the Packet List panel, look for the DNS query packet (Standard query 0x???? A www.openrice.com)
from the Info column. What “Type” of DNS query is it? Does the query message contain any “answers”?
(6 marks)
3. Look for the DNS response packet (Standard query response 0x???? A www.openrice.com). Examine
the DNS response message. What is the source port of DNS response message? (2 mark) What is the
type of address in the answer of the response message? (2 marks)
4. List the IP address of www.openrice.com. (3 marks)
5. To what IP address is the DNS query message sent? Use ipconfig to determine the IP address of your
local DNS server (If you are using OSX, you may check it in “System preferences/ Network/ Advanced/
DNS”). Are these two IP addresses the same? (3 marks)
3 If you use other operating systems, look up your operating system’s user guide for steps on opening the
console/terminal.
4 If you use other operating systems, check out http://www.whatsmydns.net/flush-dns.html for steps on clearing all
cached DNS entries on your operating system.
5 If your operating system does not have nslookup, use dig from Internet Systems Consortium’s BIND
https://www.isc.org/downloads/current
Wireshark Hands-on Assignment
Problem 3: Capturing SSL Traffic (35 marks)
The first step is to capture the packets in an SSL session. To do this, you should go to an e-commerce site
and begin the process of purchasing an item (terminate before you actually pay!). After capturing the
packets with Wireshark, you should set the filter “ssl” so that it displays only the Ethernet frames that
contain SSL records sent from and received by your host.
Questions
1. Find a pair of client and server. Find the first 8 Ethernet frames in their session. For each frame, specify
the source address and destination address, determine the number of SSL records that are included in
the frame, and list the SSL record types that are included in the frame. Draw a table to show the packet
exchange between client and server. An example of the table is shown as follows. (There might be
segments missed by Wireshark, e.g., “TCP Previous segment not captured, Ignored
Unknown Record”. Find a session that has no missing segment.) (12 marks)
Frame Source address Destination address SSL count SSL Type
Specify the IP addresses of client and server respectively. How can you tell? (3 marks)
2. Each of the SSL records begins with the same three fields (with possibly different values). One of these
fields is “content type” and has length of one byte. List all three fields and their lengths. (3 marks)
3. Expand a ClientHello record. What is the value of the content type? What is it used for? (3 marks)
4. Does the ClientHello record advertise the cipher suites it supports? Show the first cipher suite. (2 mark)
5. Find the corresponding ServerHello SSL record. Does this record specify a chosen cipher suite? Show the
chosen cipher suite. (3 mark)
6. Does the ServerHello SSL record include a nonce? If so, how long is it? What is the purpose of the client
and server nonces in SSL? (3 mark)
7. Does the ServerHello SSL record include a session ID? What is the purpose of the session ID? (3 mark)
8. Does the ServerHello SSL record contain a certificate, or is the certificate included in a separate record.
Does the certificate fit into a single Ethernet frame? (3 mark)
Wireshark Hands-on Assignment
Problem 4: Analyzing TCP Traffic (15 marks)
Download pcattcp_retrans_t.cap Capture File from the course web. The Capture File contains
Wireshark packet capture of TCP packets sending from 192.168.0.100:4480 to 192.168.0.102:5001.
From the Wireshark menu, select File è Open…. A Wireshark: Open Capture File window appears.
Select pcattcp_retrans_t.cap you downloaded from step 1 then click the [Open] button to open the
downloaded Capture File.
Wireshark displays the captured packets from pcattcp_retrans_t.cap.
Questions
(1) Draw a diagram to illustrate the handshake between 192.168.0.100:4480 and 192.168.0.102:5001. List
the length of the all packets used to complete TCP handshake. (6 marks)
(2) Finding the first TCP segment sending from 192.168.0.100:4480 after the handshake of TCP. What’s the
length of this TCP segment? (3 marks)
(3) Calculating the RTT value for the TCP segment you found in question 2. (Hint: the value of the Time
column in the packet listing window is the amount of the time, in seconds, since Wireshark tracing
began.) (6 marks)

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