Http gaia cs umass edu wireshark labs wireshark traces zip

Wireshark Lab: Ethernet and ARP v7.0 Supplement to Computer Networking: A Top-Down Approach, 7th ed., J.F. Kurose and K.W. Ross “Tell me and I forget. Show me and I remember. Involve me and I understand.” Chinese proverb

© 2005-2016 J.F Kurose and K.W. Ross, All Rights Reserved

In this lab, we’ll investigate the Ethernet protocol and the ARP protocol. Before beginning this lab, you’ll probably want to review sections 6.4.1 (Link-layer addressing and ARP) and 6.4.2 (Ethernet) in the text1. RFC 826 (ftp://ftp.rfc-editor.org/in- notes/std/std37.txt) contains the gory details of the ARP protocol, which is used by an IP device to determine the IP address of a remote interface whose Ethernet address is known. 1. Capturing and analyzing Ethernet frames Let’s begin by capturing a set of Ethernet frames to study. Do the following2:

• First, make sure your browser’s cache is empty. To do this under Mozilla Firefox V3, select Tools->Clear Recent History and check the box for Cache. For Internet Explorer, select Tools->Internet Options->Delete Files. Start up the Wireshark packet sniffer

• Enter the following URL into your browser http://gaia.cs.umass.edu/wireshark-labs/HTTP-ethereal-lab-file3.html Your browser should display the rather lengthy US Bill of Rights.

1 References to figures and sections are for the 7th edition of our text, Computer Networks, A Top-down Approach, 7th ed., J.F. Kurose and K.W. Ross, Addison-Wesley/Pearson, 2016. 2 If you are unable to run Wireshark live on a computer, you can download the zip file http://gaia.cs.umass.edu/wireshark-labs/wireshark-traces.zip and extract the file ethernet--ethereal-trace-1. The traces in this zip file were collected by Wireshark running on one of the author’s computers, while performing the steps indicated in the Wireshark lab. Once you have downloaded the trace, you can load it into Wireshark and view the trace using the File pull down menu, choosing Open, and then selecting the ethernet-ethereal-trace-1 trace file. You can then use this trace file to answer the questions below.

• Stop Wireshark packet capture. First, find the packet numbers (the leftmost column in the upper Wireshark window) of the HTTP GET message that was sent from your computer to gaia.cs.umass.edu, as well as the beginning of the HTTP response message sent to your computer by gaia.cs.umass.edu. You should see a screen that looks something like this (where packet 4 in the screen shot below contains the HTTP GET message)

• Since this lab is about Ethernet and ARP, we’re not interested in IP or higher- layer protocols. So let’s change Wireshark’s “listing of captured packets” window so that it shows information only about protocols below IP. To have Wireshark do this, select Analyze->Enabled Protocols. Then uncheck the IP box and select OK. You should now see an Wireshark window that looks like:

In order to answer the following questions, you’ll need to look into the packet details and packet contents windows (the middle and lower display windows in Wireshark). Select the Ethernet frame containing the HTTP GET message. (Recall that the HTTP GET message is carried inside of a TCP segment, which is carried inside of an IP datagram, which is carried inside of an Ethernet frame; reread section 1.5.2 in the text if you find this encapsulation a bit confusing). Expand the Ethernet II information in the packet details window. Note that the contents of the Ethernet frame (header as well as payload) are displayed in the packet contents window.

Answer the following questions, based on the contents of the Ethernet frame containing the HTTP GET message. 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 printout3 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 48-bit Ethernet address of your computer? 2. What is the 48-bit destination address in the Ethernet frame? Is this the Ethernet