Communication Networks
Lab Session 1
Wireshark - TCP/IP Protocol Analysis
Contact: avanmael@intec.ugent.be
0 Introduction
The book we are using (Computer Networking: A Top-Down Approach Featuring the
Internet) offers some labs that use Wireshark to dig into the main protocols used in the
Internet. They can be found on http://wps.aw.com/aw_kurose_network_4/0,13091,4173750,00.html .
Two of these labs will be conducted in this Lab session, as Introductory Exercises on
working with Wireshark and examining the protocols. They form chapter 1 and 2 of this lab
session.
Finally, some IBCN tailored exercises on “Transport and Application Layer Traces” are
presented in chapter 3.
HTTP-Lab:
The following paragraphs should be read, and the questions solved:
•
Par. 1: questions 1 to 7
•
Par. 4: questions 16, 17
•
Par. 5: questions 18, 19
You can skip paragraphs 2 and 3. If you don’t get the hang of things immediately, you can
solve paragraph 2 and 3 as well to get more comfortable with the Wireshark program and the
HTTP protocol.
IP-Lab:
The entire lab should be solved.
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Wireshark Lab: HTTP
Version: 2.0 (June 2007)
© 2007 J.F. Kurose, K.W. Ross. All Rights Reserved
Computer Networking: A Topth
down Approach, 4 edition.
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. Before beginning these labs, you might
want to review Section 2.2 of the text.
1. 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:
1. Start up your web browser.
2. 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).
3. Wait a bit more than one minute (we’ll see why shortly), and then begin
Wireshark packet capture.
4. Enter the following to your browser
http://gaia.cs.umass.edu/wireshark-labs/HTTP-wireshark-file1.html
Your browser should display the very simple, one-line HTML file.
5. Stop Wireshark packet capture.
Your Wireshark window should look similar to the window shown in Figure 1. If you
are unable to run Wireshark on a live network connection, you can download a packet
trace that was created when the steps above were followed.1
1
Download the zip file http://gaia.cs.umass.edu/wireshark-labs/wireshark-traces.zip and extract the file
http-ethereal-trace-1. The traces in this zip file were collected by Wireshark running on one of the author’s
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Figure 1: Wireshark Display after http://gaia.cs.umass.edu/wireshark-labs/ HTTPwireshark-file1.html has been retrieved by your browser
The example in Figure 1 shows in the packet-listing window that two HTTP messages
were captured: the GET message (from your browser to the gaia.cs.umass.edu 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 GET 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
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 http-ethereal-trace-1 trace file. The resulting display should look just like Figure 1.
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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 (which means there is hidden, undisplayed information), and
the HTTP line has a minus sign (which means that all information about the HTTP
message is displayed).
(Note: You should ignore any HTTP GET and response for favicon.ico. If you see a reference to
this file, it is your browser automatically asking the server if it (the server) has a small icon file
that should be displayed next to the displayed URL in your browser. We’ll ignore references to
this pesky file in this lab.).
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.
1. Is your browser running HTTP version 1.0 or 1.1? What version of HTTP is the
server running?
2. What languages (if any) does your browser indicate that it can accept to the
server?
3. What is the IP address of your computer? Of the gaia.cs.umass.edu server?
4. What is the status code returned from the server to your browser?
5. When was the HTML file that you are retrieving last modified at the server?
6. How many bytes of content are being returned to your browser?
7. 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 gaia.cs.umass.edu 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.
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2. The HTTP CONDITIONAL GET/response interaction
Recall from Section 2.2.6 of the text, that most web browsers perform object caching and
thus perform a conditional GET when retrieving an HTTP object. Before performing the
steps below, make sure your browser’s cache is empty. (To do this under Netscape 7.0,
select Edit->Preferences->Advanced->Cache and clear the memory and disk cache.
For Firefox, select Tools->Clear Private Data, or for Internet Explorer, select Tools>Internet Options->Delete File; these actions will remove cached files from your
browser’s cache.) Now do the following:
• Start up your web browser, and make sure your browser’s cache is cleared, as
discussed above.
• Start up the Wireshark packet sniffer
• Enter the following URL into your browser
http://gaia.cs.umass.edu/wireshark-labs/HTTP-wireshark-file2.html
Your browser should display a very simple five-line HTML file.
• Quickly enter the same URL into your browser again (or simply select the refresh
button on your browser)
• Stop Wireshark packet capture, and enter “http” in the display-filter-specification
window, so that only captured HTTP messages will be displayed later in the
packet-listing window.
• (Note: If you are unable to run Wireshark on a live network connection, you can
use the http-ethereal-trace-2 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:
8. Inspect the contents of the first HTTP GET request from your browser to the
server. Do you see an “IF-MODIFIED-SINCE” line in the HTTP GET?
9. Inspect the contents of the server response. Did the server explicitly return the
contents of the file? How can you tell?
10. Now inspect the contents of the second HTTP GET request from your browser to
the server. Do you see an “IF-MODIFIED-SINCE:” line in the HTTP GET? If
so, what information follows the “IF-MODIFIED-SINCE:” header?
11. What is the HTTP status code and phrase returned from the server in response to
this second HTTP GET? Did the server explicitly return the contents of the file?
Explain.
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3. Retrieving Long Documents
In our examples thus far, the documents retrieved have been simple and short HTML
files. Let’s next see what happens when we download a long HTML file. Do the
following:
• Start up your web browser, and make sure your browser’s cache is cleared, as
discussed above.
• Start up the Wireshark packet sniffer
• Enter the following URL into your browser
http://gaia.cs.umass.edu/wireshark-labs/HTTP-wireshark-file3.html
Your browser should display the rather lengthy US Bill of Rights.
• 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-3 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.)
In the packet-listing window, you should see your HTTP GET message, followed by a
multiple-packet response to your HTTP GET request. This multiple-packet response
deserves a bit of explanation. Recall from Section 2.2 (see Figure 2.9 in the text) that the
HTTP response message consists of a status line, followed by header lines, followed by a
blank line, followed by the entity body. In the case of our HTTP GET, the entity body in
the response is the entire requested HTML file. In our case here, the HTML file is rather
long, and at 4500 bytes is too large to fit in one TCP packet. The single HTTP response
message is thus broken into several pieces by TCP, with each piece being contained
within a separate TCP segment (see Figure 1.20 in the text). Each TCP segment is
recorded as a separate packet by Wireshark, and the fact that the single HTTP response
was fragmented across multiple TCP packets is indicated by the “TCP segment of a
reassembled PDU” phrase displayed by Wireshark. We stress here that there is no
“reassembled ” message in HTTP!
Answer the following questions:
12. How many HTTP GET request messages were sent by your browser?
13. How many data-containing TCP segments were needed to carry the single HTTP
response?
14. What is the status code and phrase associated with the response to the HTTP GET
request?
15. Are there any HTTP status lines in the transmitted data associated with a TCPinduced “reassembled”?
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4. HTML Documents with Embedded Objects
Now that we’ve seen how Wireshark displays the captured packet traffic for large HTML
files, we can look at what happens when your browser downloads a file with embedded
objects, i.e., a file that includes other objects (in the example below, image files) that are
stored on another server(s).
Do the following:
• Start up your web browser, and make sure your browser’s cache is cleared, as
discussed above.
• Start up the Wireshark packet sniffer
• Enter the following URL into your browser
http://gaia.cs.umass.edu/wireshark-labs/HTTP-wireshark-file4.html
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. Our publisher’s logo is
retrieved from the www.aw-bc.com web site. The image of our book’s cover is
stored at the manic.cs.umass.edu server.
• 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:
16. How many HTTP GET request messages were sent by your browser? To which
Internet addresses were these GET requests sent?
17. Can you tell whether your browser downloaded the two images serially, or
whether they were downloaded from the two web sites in parallel? Explain.
5 HTTP Authentication
Finally, let’s try visiting a web site that is password-protected and examine the sequence
of HTTP message exchanged for such a site. The URL
http://gaia.cs.umass.edu/wireshark-labs/protected_pages/HTTP-wireshark-file5.html is
password protected. The username is “eth-students” (without the quotes), and the
password is “networks” (again, without the quotes). So let’s access this “secure”
password-protected site. Do the following:
• Make sure your browser’s cache is cleared, as discussed above, and close down
your browser. Then, start up your browser
• Start up the Wireshark packet sniffer
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•
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Enter the following URL into your browser
http://gaia.cs.umass.edu/wireshark-labs/protected_pages/HTTP-wiresharkfile5.html
Type the requested user name and password into the pop up box.
Stop Wireshark packet capture, and enter “http” in the display-filter-specification
window, so that only captured HTTP messages will be displayed later in the
packet-listing window.
(Note: If you are unable to run Wireshark on a live network connection, you can
use the http-ethereal-trace-5 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.)
Now let’s examine the Wireshark output. You might want to first read up on HTTP
authentication by reviewing the easy-to-read material on “HTTP Access Authentication
Framework” at http://frontier.userland.com/stories/storyReader$2159
Answer the following questions:
18. What is the server’s response (status code and phrase) in response to the initial
HTTP GET message from your browser?
19. When your browser’s sends the HTTP GET message for the second time, what
new field is included in the HTTP GET message?
The username (eth-students) and password (networks) that you entered are encoded
in the string of characters (ZXRoLXN0dWRlbnRzOm5ldHdvcmtz) following
the “Authorization: Basic” header in the client’s HTTP GET message. While it
may appear that your username and password are encrypted, they are simply encoded in a
format known as Base64 format. The username and password are not encrypted! To see
this, go to http://www.securitystats.com/tools/base64.php and enter the base64-encoded
string ZXRoLXN0dWRlbnRz and press decode. Voila! You have translated
from Base64 encoding to ASCII encoding, and thus should see your username! To view
the password, enter the remainder of the string Om5ldHdvcmtz and press decode. Since
anyone can download a tool like Wireshark and sniff packets (not just their own) passing
by their network adaptor, and anyone can translate from Base64 to ASCII (you just did
it!), it should be clear to you that simple passwords on WWW sites are not secure unless
additional measures are taken.
Fear not! As we will see in Chapter 8, there are ways to make WWW access more secure.
However, we’ll clearly need something that goes beyond the basic HTTP authentication
framework!
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Wireshark Lab: IP
Version: 2.0
© 2007 J.F. Kurose, K.W. Ross. All Rights Reserved
Computer Networking: A Topth
down Approach, 4 edition.
In this lab, we’ll investigate the IP protocol, focusing on the IP datagram. We’ll do so by
analyzing a trace of IP datagrams sent and received by an execution of the traceroute
program (the traceroute program itself is explored in more detail in the Wireshark
ICMP lab). We’ll investigate the various fields in the IP datagram, and study IP
fragmentation in detail.
Before beginning this lab, you’ll probably want to review sections 1.4.3 in the text and
section 3.4 of RFC 2151 [ftp://ftp.rfc-editor.org/in-notes/rfc2151.txt] to update yourself
on the operation of the traceroute program. You’ll also want to read Section 4.4 in
the text, and probably also have RFC 791 [ftp://ftp.rfc-editor.org/in-notes/rfc791.txt] on
hand as well, for a discussion of the IP protocol.1
1. Capturing packets from an execution of traceroute
In order to generate a trace of IP datagrams for this lab, we’ll use the traceroute
program to send datagrams of different sizes towards some destination, X. Recall that
traceroute operates by first sending one or more datagrams with the time-to-live
(TTL) field in the IP header set to 1; it then sends a series of one or more datagrams
towards the same destination with a TTL value of 2; it then sends a series of datagrams
towards the same destination with a TTL value of 3; and so on. Recall that a router must
decrement the TTL in each received datagram by 1 (actually, RFC 791 says that the
router must decrement the TTL by at least one). If the TTL reaches 0, the router returns
an ICMP message (type 11 – TTL-exceeded) to the sending host. As a result of this
behavior, a datagram with a TTL of 1 (sent by the host executing traceroute) will
cause the router one hop away from the sender to send an ICMP TTL-exceeded message
back to the sender; the datagram sent with a TTL of 2 will cause the router two hops
away to send an ICMP message back to the sender; the datagram sent with a TTL of 3
1
All references to the text in this lab are to Computer Networking: A Top-down Approach, 4th edition.
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will cause the router three hops away to send an ICMP message back to the sender; and
so on. In this manner, the host executing traceroute can learn the identities of the
routers between itself and destination X by looking at the source IP addresses in the
datagrams containing the ICMP TTL-exceeded messages.
We’ll want to run traceroute and have it send datagrams of various lengths.
•
•
Windows. The tracert program (used for our ICMP Wireshark lab) provided
with Windows does not allow one to change the size of the ICMP echo request
(ping) message sent by the tracert program. A nicer Windows traceroute
program is pingplotter, available both in free version and shareware versions at
http://www.pingplotter.com. Download and install pingplotter, and test it out by
performing a few traceroutes to your favorite sites. The size of the ICMP echo
request message can be explicitly set in pingplotter by selecting the menu item
Edit-> Options->Packet Options and then filling in the Packet Size field. The
default packet size is 56 bytes. Once pingplotter has sent a series of packets with
the increasing TTL values, it restarts the sending process again with a TTL of 1,
after waiting Trace Interval amount of time. The value of Trace Interval and the
number of intervals can be explicitly set in pingplotter.
Linux/Unix. With the Unix traceroute command, the size of the UDP
datagram sent towards the destination can be explicitly set by indicating the
number of bytes in the datagram; this value is entered in the traceroute
command line immediately after the name or address of the destination. For
example, to send traceroute datagrams of 2000 bytes towards
gaia.cs.umass.edu, the command would be:
%traceroute gaia.cs.umass.edu 2000
Do the following:
• Start up Wireshark and begin packet capture (Capture->Option) and then press
OK on the Wireshark Packet Capture Options screen (we’ll not need to select any
options here).
• If you are using a Windows platform, start up pingplotter and enter the name of a
target destination in the “Address to Trace Window.” Enter 3 in the “# of times to
Trace” field, so you don’t gather too much data. Select the menu item Edit>Advanced Options->Packet Options and enter a value of 56 in the Packet Size
field and then press OK. Then press the Trace button. You should see a
pingplotter window that looks something like this:
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Next, send a set of datagrams with a longer length, by selecting Edit->Advanced
Options->Packet Options and enter a value of 2000 in the Packet Size field and
then press OK. Then press the Resume button.
Finally, send a set of datagrams with a longer length, by selecting Edit>Advanced Options->Packet Options and enter a value of 3500 in the Packet Size
field and then press OK. Then press the Resume button.
Stop Wireshark tracing.
•
If you are using a Unix platform, enter three traceroute commands, one with
a length of 56 bytes, one with a length of 2000 bytes, and one with a length of
3500 bytes.
Stop Wireshark tracing.
If you are unable to run Wireshark on a live network connection, you can download a
packet trace file that was captured while following the steps above on one of the author’s
Windows computers2. You may well find it valuable to download this trace even if
you’ve captured your own trace and use it, as well as your own trace, when you explore
the questions below.
2
Download the zip file http://gaia.cs.umass.edu/wireshark-labs/wireshark-traces.zip and extract the file ipethereal-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 ip-ethereal-trace-1 trace file.
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2. A look at the captured trace
In your trace, you should be able to see the series of ICMP Echo Request (in the case of
Windows machine) or the UDP segment (in the case of Unix) sent by your computer and
the ICMP TTL-exceeded messages returned to your computer by the intermediate
routers. In the questions below, we’ll assume you are using a Windows machine; the
corresponding questions for the case of a Unix machine should be clear. 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 printout 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. Select the first ICMP Echo Request message sent by your computer, and expand
the Internet Protocol part of the packet in the packet details window.
What is the IP address of your computer?
2. Within the IP packet header, what is the value in the upper layer protocol field?
3. How many bytes are in the IP header? How many bytes are in the payload of the
IP datagram? Explain how you determined the number of payload bytes.
4. Has this IP datagram been fragmented? Explain how you determined whether or
not the datagram has been fragmented.
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Next, sort the traced packets according to IP source address by clicking on the Source
column header; a small downward pointing arrow should appear next to the word Source.
If the arrow points up, click on the Source column header again. Select the first ICMP
Echo Request message sent by your computer, and expand the Internet Protocol portion
in the “details of selected packet header” window. In the “listing of captured packets”
window, you should see all of the subsequent ICMP messages (perhaps with additional
interspersed packets sent by other protocols running on your computer) below this first
ICMP. Use the down arrow on your keyboard to move through the ICMP messages sent
by your computer.
5. Which fields in the IP datagram always change from one datagram to the next
within this series of ICMP messages sent by your computer?
6. Which fields stay constant? Which of the fields must stay constant? Which fields
must change? Why?
7. Describe the pattern you see in the values in the Identification field of the IP
datagram
Next (with the packets still sorted by source address) find the series of ICMP TTLexceeded replies sent to your computer by the nearest (first hop) router.
8. What is the value in the Identification field and the TTL field?
9. Do these values remain unchanged for all of the ICMP TTL-exceeded replies sent
to your computer by the nearest (first hop) router? Why?
Fragmentation
Sort the packet listing according to time again by clicking on the Time column.
10. Find the first ICMP Echo Request message that was sent by your computer after
you changed the Packet Size in pingplotter to be 2000. Has that message been
fragmented across more than one IP datagram? [Note: if you find your packet has
not been fragmented, you should download the zip file
http://gaia.cs.umass.edu/wireshark-labs/wireshark-traces.zip and extract the ipethereal-trace-1packet trace. If your computer has an Ethernet interface, a packet
size of 2000 should cause fragmentation.3]
11. Print out the first fragment of the fragmented IP datagram. What information in
the IP header indicates that the datagram been fragmented? What information in
3
The packets in the ip-ethereal-trace-1 trace file in http://gaia.cs.umass.edu/wireshark-labs/wiresharktraces.zip are all less that 1500 bytes. This is because the computer on which the trace was gathered has an
Ethernet card that limits the length of the maximum IP packet to 1500 bytes (40 bytes of TCP/IP header
data and 1460 bytes of upper-layer protocol payload). This 1500 byte value is the standard maximum
length allowed by Ethernet. If your trace indicates a datagram longer 1500 bytes, and your computer is
using an Ethernet connection, then Wireshark is reporting the wrong IP datagram length; it will likely also
show only one large IP datagram rather than multiple smaller datagrams.. This inconsistency in reported
lengths is due to the interaction between the Ethernet driver and the Wireshark software. We recommend
that if you have this inconsistency, that you perform this lab using the ip-ethereal-trace-1 trace file.
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the IP header indicates whether this is the first fragment versus a latter fragment?
How long is this IP datagram?
12. Print out the second fragment of the fragmented IP datagram. What information in
the IP header indicates that this is not the first datagram fragment? Are the more
fragments? How can you tell?
13. What fields change in the IP header between the first and second fragment?
Now find the first ICMP Echo Request message that was sent by your computer after you
changed the Packet Size in pingplotter to be 3500.
14. How many fragments were created from the original datagram?
15. What fields change in the IP header among the fragments?
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3 Transport and Application Layer Traces
3.1
•
Proxy Server and Client (02.proxy.server.cap & 02.proxy.client.cap)
Introduction
Networks usually incorporate many mechanisms to reduce the amount of traffic in the
network and/or the load on the servers. In this exercise, we will focus on one of these
mechanisms, built in the HTTP protocol more specifically. This is an illustration of the use of
a proxy server, along with a similar technique built in the browser (local caching).
You receive two traces in this case: at the same time, as packets on the client side and the
server side were captured.
•
Network Topology
This trace was taken on a network with one subnet (157.193.122.0/24) of 254 hosts. The
machine with 157.193.122.1 as address is the gateway to other networks and the internet. This
network is an IP network, using Ethernet as data link layer protocol. All servers (IP’s
157.193.122.1-20) and routers are on the same switch while the user PC’s (IP’s larger then
157.193.122.20) are connected using hubs. An uplink from the hubs to the switch connects
the user machines to the servers.
The packets were captured on the client (157.193.122.155). The machine with IP
157.193.122.17 is the proxy server for this subnet.
The server is at 213.118.200.13, somewhere in the Telenet (pandora.be) domain. Observing
the two traces, try to answer the following questions.
•
Questions
Q1: Describe what is being done in the first three packets. Describe the relations between the
subsequent packets, and why they are sent.
Q2: What has happened during this trace? Who requested what?
Q3: What is the function of the proxy server? Why is it used? Motivate!
Q4: How does a proxy server work? Substantiate by means of elements from the packet
headers.
Q5: Observing the second get request and reply, where does the obtained file come from?
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3.2
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Additional question (Capture File: 03.CAP.cap)
Network Topology
Not relevant in this context.
•
Questions
Q1: What exactly is happening here, i.e. which tool is doing what? There is no need to give
the exact name of the program if you can explain what is happening.
Q2: Which hosts -or networks- are affected?
Q3: How does this tool work? What is it trying to achieve and how does it do that?
Q4: Can you think of a way from preventing this tool to work properly?
Appendix: hints on this lab
Practical organization; useful hints
This document must be completed by the end of the lab session. After the lab session
Wireshark1, you can keep the lab description sheets as a reference to study the labs. An
example solution will be provided on the Minerva site by next week.
The next Wireshark lab session within 2 weeks - Wireshark2 - will be quoted and the results
will have to be handed in after the session.
All questions are related to Wireshark capture files, which can be obtained from the Minerva
website. When necessary, you will get the topology and extra information on the network
where the packets were captured.
As a reminder: some useful hints with regard to Wireshark:
•
Disable the DNS and MAC address translation when loading the files, in order to make
the files load faster. To do so, Choose “Preferences” from the “Edit” menu, click “Name
Resolution”, disable everything and Apply.
•
Following an entire TCP stream is done by right clicking on a packet that belongs to that
stream, and selecting “follow TCP stream” from the menu.
•
It is possible to open multiple Wireshark windows, to make it easier to compare traces
with each other.
If you want to experiment a little further, Wireshark is available for download from
http://www.wireshark.org/ (and yes, it is GNU freeware).
Further labs…
… can be found on the website http://wps.aw.com/aw_kurose_network_4/0,13091,4173750,00.html , and can be used as self study for further training on Wireshark and protocols when
this lab session has ended.
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