Computer Networks- Wireshark TCP project

Computer Networks- Wireshark TCP project. I have attached the details thank you. Please if you dont know please dont take responsibility.
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Wireshark Lab: TCP
In this lab, we’ll investigate the behavior of the celebrated TCP protocol in detail. We’ll
do so 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 your
computer to a remote server
Before beginning this lab, you’ll probably want to review sections 3.5 and 3.7 in the
text1.
Preliminary Steps:
1. Disable IPv6, if applicable.
2. Disable Large Send Offload (also called TCP Segmentation Offload), if
applicable.
Include screenshots whenever possible. You will lose (many) points if you do not provide
necessary screenshots.
I prepared a video that shows how to capture packets and answer the questions.
https://1drv.ms/v/s!AscAkmu7rcZ6g6cBDsuXYRCxCGsgvg
1. Capturing a bulk TCP transfer from your computer to a remote
server
Before beginning our exploration of TCP, we’ll need to use Wireshark to obtain a packet
trace of the TCP transfer of a file from your computer to a remote server. You’ll do so by
accessing a Web page that will allow you to enter the name of a file stored on your
computer (which contains the ASCII text of Alice in Wonderland), and then transfer the
file to a Web server using the HTTP POST method (see section 2.2.3 in the text). We’re
using the POST method rather than the GET method as we’d like to transfer a large
amount of data from your computer to another computer. Of course, we’ll be running
Wireshark during this time to obtain the trace of the TCP segments sent and received
from your computer.
Do the following:
• Start up your web browser. Go to http://gaia.cs.umass.edu/wireshark-labs/alice.txt
and retrieve an ASCII copy of Alice in Wonderland. Store this file somewhere on
your computer.
1
References to figures and sections are for the 6th edition of our text, Computer Networks, A Top-down
Approach, 6th ed., J.F. Kurose and K.W. Ross, Addison-Wesley/Pearson, 2012.
•
•
Next go to http://gaia.cs.umass.edu/wireshark-labs/TCP-wireshark-file1.html.
You should see a screen that looks like:
•
Use the Browse button in this form to enter the name of the file (full path name)
on your computer containing Alice in Wonderland (or do so manually). Don’t yet
press the “Upload alice.txt file” button.
Now start up Wireshark and begin packet capture (Capture->Start) and then press
OK on the Wireshark Packet Capture Options screen (we’ll not need to select any
options here).
Returning to your browser, press the “Upload alice.txt file” button to upload the
file to the gaia.cs.umass.edu server. Once the file has been uploaded, a short
congratulations message will be displayed in your browser window.
Stop Wireshark packet capture. Your Wireshark window should look similar to
the window shown below.
•
•
•
2. A first look at the captured trace
Before analyzing the behavior of the TCP connection in detail, let’s take a high level
view of the trace.
• First, 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 specification window towards the top of the Wireshark window.
What you should see is series of TCP and HTTP messages between your computer and
gaia.cs.umass.edu. You should see the initial three-way handshake containing a SYN
message. You should see an HTTP POST message. Depending on the version of
Wireshark you are using, you might see a series of “HTTP Continuation” messages being
sent from your computer to gaia.cs.umass.edu. Recall from our discussion in the earlier
HTTP Wireshark lab, that is no such thing as an HTTP Continuation message – this is
Wireshark’s way of indicating that there are multiple TCP segments being used to carry a
single HTTP message. In more recent versions of Wireshark, you’ll see “[TCP segment
of a reassembled PDU]” in the Info column of the Wireshark display to indicate that this
TCP segment contained data that belonged to an upper layer protocol message (in our
case here, HTTP). You should also see TCP ACK segments being returned from
gaia.cs.umass.edu to your computer.
Answer the following questions according to your captured packets. Whenever possible,
when answering a question, you should hand in a printout of the packet(s) within the
trace that you used to answer the question asked. Annotate the printout2 to explain your
answer. To print a packet, use File->Print, choose Selected packet only, choose Packet
summary line, and select the minimum amount of packet detail that you need to answer
the question.
1. 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? To answer this question, it’s
probably easiest to select an HTTP message and explore the details of the TCP
packet used to carry this HTTP message, using the “details of the selected packet
header window” (refer to Figure 2 in the “Getting Started with Wireshark” Lab if
you’re uncertain about the Wireshark windows.
2. What is the IP address of gaia.cs.umass.edu? On what port number is it sending
and receiving TCP segments for this connection?
We will use the packet trace that you have captured to study TCP behavior in the rest of
this lab.
3. TCP Basics
Answer the following questions for the TCP segments:
3. 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? What is it
in the segment that identifies the segment as a SYN segment?
4. 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? 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 sequence number of the TCP segment containing the HTTP POST
command? Note that in order to find the POST command, you’ll need to dig into
the packet content field at the bottom of the Wireshark window, looking for a
segment with a “POST” within its DATA field.
6. Consider the TCP segment containing the HTTP POST as the first segment in the
TCP connection. What are the sequence numbers of the first six segments in the
TCP connection (including the segment containing the HTTP POST)? At what
time was each segment sent? Select an arbitrary ACK segment (which is for a
TCP data segment sent by your client to the server) sent back by the web server;
when was it received? When was the corresponding TCP data segment sent?
What do we mean by “annotate”? If you hand in a paper copy, please highlight where in the printout
you’ve found the answer and add some text (preferably with a colored pen) noting what you found in what
you ‘ve highlight. If you hand in an electronic copy, it would be great if you could also highlight and
annotate.
2
Please calculate the RTT (Round Trip Time) for the corresponding TCP data
segment and its ACK.
7. What is the length of each of the first six TCP segments? Based on this
information, what’s the MSS (Maximum Segment Size)?
8. What is the minimum amount of available buffer space advertised at the receiver
for the entire trace?
9. Are there any retransmitted segments in the trace file? What did you check for (in
the trace) in order to answer this question?
10. How much data does the receiver typically acknowledge in an ACK? Providing
the information for one ACK is enough. You need to first pick the ACK, and then
find the corresponding TCP data segment sent by your client, and then report the
number of data bytes in the TCP segment’s payload.

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