Intro to Basic HTTP
Having gotten our feet wet with the Wireshark packet sniffer in the introductory lab, we’re now ready 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.
The Basic HTTP GET/response interaction
Let’s begin our exploration of HTTP by downloading a very simple HTML file - one that is very short, and contains no embedded objects. Do the following:
- Start up your web browser.
- Start up the Wireshark packet sniffer, as described in the Introductory lab (but stop the 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.
- Enter the following URL in your browser
- Your browser should display the very simple, HTML file.
- Stop Wireshark packet capture.
Your Wireshark window should look similar to the window shown below
The example above shows in the packet-listing window that two HTTP messages were captured: the GET message (from your browser to the steamclown.org web server) 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, un-displayed 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 (e.g., for our classes, we ask that students markup or annotate electronic copies with text in a colored font. Best to Screen capture the wireshark image and paste into a PPT, then save as PDF to turn in to the Jupiter grading system. See the end of this lab for text capture instructions).
Basic HTTP GET/response Quiz Questions
- 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 IP address of your computer? Of the steamclown.org 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?
- How many bytes of content are being returned to your browser?
- 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.
In your answer to question 5 above, you might have been surprised to find that the document you just retrieved was last modified within a minute before you downloaded the document. That’s because (for this particular file), the steamclown.org server is setting the file’s last-modified time to be the current time, and is doing so once per minute. Thus, if you wait a minute between accesses, the file will appear to have been recently modified, and hence your browser will download a “new” copy of the document
How To Capture And Markup Your Assignment
To capture the packet data and save it to a Google or Word doc and then turn it in as a PDF do the following:
- in wireshark, capture the packets, and highlight the specific one you want to look at
- in the Packet details frame "right" mouse click and select "expand all"
- Then you will want to copy the packet data and paste it into a Google or Word doc
- Paste this in a Doc and high lite the sections as you answer the Lab questions
