WS Lab 8
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Midlands Technical College *
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Industrial Engineering
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Dec 6, 2023
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IST 227
Lab 8
Lab 8 –
Transport Layer Protocols (TCP and UDP)
*Disclaimer – All tools and skills used during labs are the responsibility of the student,
neither MTC nor the instructor will not be held liable for any damage to personal or
corporate systems or networks. Before you capture any network traffic, ensure you have
permission to listen to the network traffic. If you are an IT staff member performing these
tasks in a corporate environment, obtain written permission to listen to network traffic for
troubleshooting, optimization, security, and application analysis.
In this first part of the lab you will investigate the behavior of the TCP protocol in
detail by analyzing a trace of the TCP segments sent and received in transferring a
150KB file (containing the text of Lewis Carrol’s
Alice’s Adventures in Wonderland
)
from a computer to a remote server. You’ll study TCP’s use of sequence and
acknowledgement numbers for providing reliable data transfer.
1.
Launch
Wireshark
, click the
File -> Open
on the menu bar or the
Open
button
on the tool bar and select the file labeled
Lab8_01.pcapng
to open
the capture.
a.
How many packets do you see in this capture?
190
b.
Filter the packets displayed in the Wireshark window by
entering “tcp” (lowercase, no quotes, and don’t forget to
press return after entering!) into the display filter bar.
i.
You should see a series of TCP and HTTP messages
between a host and gaia.cs.umass.edu.
ii.
You should see the initial three-way handshake
containing a SYN message.
iii.
You should see an HTTP POST message.
1
IST 227
Lab 8
c.
Look at frame 3 What is the IP address and TCP port number
used by the client computer (source) that is transferring the
file to gaia.cs.umass.edu?
IP address is 10.65.10.6
Port Number is 35832
d.
What is the IP address of gaia.cs.umass.edu? On what port
number is it sending and receiving TCP segments for this
connection?
128.119. 245.12 and the TCP port number is 80.
2.
What is the sequence number of the TCP SYN segment that is used
to initiate the TCP connection between the client computer and
gaia.cs.umass.edu?
0
2457377136 raw
What is it in the segment that identifies the segment as a SYN
segment? 1 29606827
3.
What is the sequence number of the SYNACK segment sent by
gaia.cs.umass.edu to the client computer in reply to the SYN? What
is the value of the Acknowledgement field in the SYNACK segment?
4.
How did gaia.cs.umass.edu determine that value? What is it in the
segment that identifies the segment as a SYNACK segment?
5.
What is the protocol number for UDP? Give your answer in both
hexadecimal and decimal notation (
hint: look at the protocol field of the
IP packet containing your selected UDP segment
).
2
IST 227
Lab 8
In this second part of the lab you will investigate the behavior of the UDP protocol, a
streamlined, no-frills protocol, in detail by analyzing a trace of UDP segments.
1.
Launch Wireshark, click the File -> Open on the menu bar or the
Open button on the tool bar and select the file labeled
Lab8_02.pcapng to open the capture.
a.
How many packets do you see in this capture?
b.
Filter the packets displayed in the Wireshark window by
entering “udp” (lowercase, no quotes, and don’t forget to
press return after entering!) into the display filter bar.
c.
What types of (protocol) messages do you see? Why?
d.
Select any one UDP packet from your trace. From this packet,
determine how many fields there are in the UDP header. (You
shouldn’t look in the textbook! Answer these questions
directly from what you observe in the packet trace.)
e.
Name these fields:
2.
By consulting the displayed information in Wireshark’s packet
content field for this packet, determine the length (in bytes) of each
of the UDP header fields (
hint: select any UDP segment and right click in
the Packet Bytes Pane and select the option “…as bits” to show the packet
data as bits and sum the total bits for all header fields you listed in the
previous step and convert them to bytes.
)
a.
The value in the Length field is the length of what?
b.
What is the maximum number of bytes that can be included in
a UDP payload?
c.
What is the largest possible source port number?
3.
What is the protocol number for UDP? Give your answer in both
hexadecimal and decimal notation (
hint: look at the protocol field of the
IP packet containing your selected UDP segment
).
3
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