Answer the following questions, by opening the Wireshark captured packet file tcp-ethereal-trace-1 (that is download the trace and open that trace in Wireshark; see footnote 2). Annotate your screenshots 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 gaiawebsite(For details go to attached file) ? 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 website?(For details go to attached file) On what port number is it sending and receiving TCP segments for this connectionIf you have been able to create your own trace, answer the following question:
3. What is the IP address and TCP port number used by your client computer (source) to transfer the file to gaiawebsite(For details go to attached file) ?
Since this lab is about TCP rather than HTTP, let's change Wireshark's "listing of captured packets" window so that it shows information about the TCP segments containing the HTTP messages, rather than about the HTTP messages. To have Wireshark do this, select Analyze->Enabled Protocols. Then uncheck the HTTP box and select OK. You should now see a Wireshark window that looks like:
TCP Basics
Answer the following questions for the TCP segments and show annotated screenshots:
4. What is the sequence number of the TCP SYN segment that is used to initiate the TCP connection between the client computer and gaiawebsite(For details go to attached file) ? What is it in the segment that identifies the segment as a SYN segment?
5. What is the sequence number of the SYNACK segment sent by gaiawebsite(For details go to attached file) to the client computer in reply to the SYN? What is the value of the Acknowledgement field in the SYNACK segment? How did gaiawebsite(For details go to attached file) determine that value? What is it in the segment that identifies the segment as a SYNACK segment?
6. 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.
7. 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? When was the ACK for each segment received? Given the difference between when each TCP segment was sent, and when its acknowledgement was received, what is the RTT value for each of the six segments?
What is the Estimated RTT value (see Section 3.5.3, page 242 in text) after the receipt of each ACK? Assume that the val ue of the EstimatedRTT is equal to the measured RTT for the first segment, and then is computed using the EstimatedRTT equation on page 242 for all subsequent segments.
Note: Wireshark has a nice feature that allows you to plot the RTT for each of the TCP segments sent. Select a TCP segment in the "listing of captured packets" window that is being sent from the client to the gaia website(For details go to attached file) server. Then select: Statistics->TCP Stream Graph- >Round Trip Time Graph.
8. What is the length of each of the first six TCP segments?
9. What is the minimum amount of available buffer space advertised at the received for the entire trace? Does the lack of receiver buffer space ever throttle the sender?
10. Are there any retransmitted segments in the trace file? What did you check for (in the trace) in order to answer this question?
11. How much data does the receiver typically acknowledge in an ACK? Can you identify cases where the receiver is ACKing every other received segment (see Table 3.2 on page 250 in the text).
12. What is the throughput (bytes transferred per unit time) for the TCP connection? Explain how you calculated this value.
TCP congestion control in action
Let's now examine the amount of data sent per unit time from the client to the server. Rather than (tediously!) calculating this from the raw data in the Wireshark window, we'll use one of Wireshark's TCP graphing utilities - Time-Sequence-Graph(Stevens) - to plot out data.
• Select a TCP segment in the Wireshark's "listing of captured-packets" window. Then select the menu : Statistics->TCP Stream Graph-> Time-Sequence- Graph(Stevens). You should see a plot that looks similar to the following plot, which was created from the captured packets in the packet trace tcp-ethereal- trace-1.
Here, each dot represents a TCP segment sent, plotting the sequence number of the segment versus the time at which it was sent. Note that a set of dots stacked above each other represents a series of packets that were sent back-to-back by the sender.
13. Use the Time-Sequence-Graph(Stevens) plotting tool to view the sequence number versus time plot of segments being sent from the client to the gaiawebsite(For details go to attached file) server. Can you identify where TCP's slowstart phase begins and ends, and where congestion avoidance takes over? Comment on ways in which the measured data differs from the idealized behavior of TCP that we've studied in the text.
14.Answer each of two questions above for the trace that you have gathered when you transferred a file from your computer to gaiawebsite(For details go to attached file) . Make sure you clearly annotate screenshots and show which two questions you've answered for this question.
15.How long did it take to complete the lab? Did you feel this lab was helpful or valuable? Please explain your answer.
Attachment:- Wireshark TCP.rar