Computer Security Lab 5 Wireshark 2
Computer Security Lab 5 Wireshark 2
Computer Security Lab 5 Wireshark 2
Objective:
We’re going to use Wireshark to investigate protocols in operation. In this lab, we’ll explore several
aspects of the HTTP protocol: the basic GET/response interaction, HTTP message formats, retrieving
large HTML files, retrieving HTML files with embedded objects, and HTTP authentication and security.
• Start up the Wireshark packet sniffer, as described in the Introductory lab (but don’t yet begin
packet capture). Enter “http” (just the letters, not the quotation marks) in the display-filter-
specification window, so that only captured HTTP messages will be displayed later in the packet-
listing window. (We’re only interested in the HTTP protocol here, and don’t want to see the
clutter of all captured packets).
• Wait a bit more than one minute (we’ll see why shortly), and then begin Wireshark packet
capture.
http:// 178.62.81.25/wireshark-labs/HTTP-wireshark-file1.html
• Your browser should display the very simple, one-line HTML file.
Your Wireshark window should look similar to the window shown in Figure 1.
The example in Figure 1 shows in the packet-listing window that two HTTP messages were captured: the
GET message and the response message from the server to your browser. The packet-contents window
shows details of the selected message (in this case the HTTP OK message, which is highlighted in the
packet-listing window). Recall that since the HTTP message was carried inside a TCP segment, which was
carried inside an IP datagram, which was carried within an Ethernet frame, Wireshark displays the
Frame, Ethernet, IP, and TCP packet information as well. We want to minimize the amount of non-HTTP
data displayed (we’re interested in HTTP here, and will be investigating these other protocols is later
labs), so make sure the boxes at the far left of the Frame, Ethernet, IP and TCP information have a plus
sign or a right-pointing triangle (which means there is hidden, undisplayed information), and the HTTP
line has a minus sign or a down-pointing triangle (which means that all information about the HTTP
message is displayed).
By looking at the information in the HTTP GET and response messages, answer the following questions.
When answering the following questions, you should print out the GET and response messages (see the
introductory Wireshark lab for an explanation of how to do this) and indicate where in the message
you’ve found the information that answers the following questions. When you hand in your assignment,
annotate the output so that it’s clear where in the output you’re getting the information for your answer.
• Is your browser running HTTP version 1.0 or 1.1? What version of HTTP is the server running?
• What languages (if any) does your browser indicate that it can accept to the server?
• What is the status code returned from the server to your browser?
• When was the HTML file that you are retrieving last modified at the server?
• By inspecting the raw data in the packet content window, do you see any headers within the
data that are not displayed in the packet-listing window? If so, name one.
Do the following:
• Start up your web browser, and make sure your browser’s cache is cleared, as discussed above.
• Your browser should display a short HTML file with two images. These two images are
referenced in the base HTML file. That is, the images themselves are not contained in the HTML;
instead the URLs for the images are contained in the downloaded HTML file. As discussed in the
textbook, your browser will have to retrieve these logos from the indicated web sites.
• Stop Wireshark packet capture, and enter “http” in the display-filter-specification window, so
that only captured HTTP messages will be displayed.
• (Note: If you are unable to run Wireshark on a live network connection, you can use the http-
ethereal-trace-4 packet trace to answer the questions below; see footnote 1. This trace file was
gathered while performing the steps above on one of the author’s computers.)
Answer the following questions:
• How many HTTP GET request messages did your browser send? To which Internet addresses
were these GET requests sent?
• Can you tell whether your browser downloaded the two images serially, or whether they were
downloaded from the two web sites in parallel? Explain.