3.3.3.4 Lab - Using Wireshark To View Network Traffic
3.3.3.4 Lab - Using Wireshark To View Network Traffic
3.3.3.4 Lab - Using Wireshark To View Network Traffic
Topology
Objectives
Part 1: (Optional) Download and Install Wireshark
Part 2: Capture and Analyze Local ICMP Data in Wireshark
Explain why MAC addresses for remote hosts are different than the MAC addresses of local hosts.
Background / Scenario
Wireshark is a software protocol analyzer, or "packet sniffer" application, used for network troubleshooting,
analysis, software and protocol development, and education. As data streams travel back and forth over the
network, the sniffer "captures" each protocol data unit (PDU) and can decode and analyze its content
according to the appropriate RFC or other specifications.
Wireshark is a useful tool for anyone working with networks and can be used with most labs in the CCNA
courses for data analysis and troubleshooting. This lab provides instructions for downloading and installing
Wireshark, although it may already be installed. In this lab, you will use Wireshark to capture ICMP data
packet IP addresses and Ethernet frame MAC addresses.
Required Resources
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Additional PC(s) on a local-area network (LAN) will be used to reply to ping requests.
Part 1:
Wireshark has become the industry standard packet-sniffer program used by network engineers. This open
source software is available for many different operating systems, including Windows, Mac, and Linux. In Part
1 of this lab, you will download and install the Wireshark software program on your PC.
Note: If Wireshark is already installed on your PC, you can skip Part 1 and go directly to Part 2. If Wireshark
is not installed on your PC, check with your instructor about your academys software download policy.
c.
Choose the software version you need based on your PCs architecture and operating system. For
instance, if you have a 64-bit PC running Windows, choose Windows Installer (64-bit).
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c.
If this is the first time to install Wireshark, or after you have completed the uninstall process, you will
navigate to the Wireshark Setup wizard. Click Next.
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d. Continue advancing through the installation process. Click I Agree when the License Agreement window
displays.
e. Keep the default settings on the Choose Components window and click Next.
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f.
g. You can change the installation location of Wireshark, but unless you have limited disk space, it is
recommended that you keep the default location.
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h. To capture live network data, WinPcap must be installed on your PC. If WinPcap is already installed on
your PC, the Install check box will be unchecked. If your installed version of WinPcap is older than the
version that comes with Wireshark, it is recommend that you allow the newer version to be installed by
clicking the Install WinPcap x.x.x (version number) check box.
i.
j.
Wireshark starts installing its files and a separate window displays with the status of the installation. Click
Next when the installation is complete.
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a. Open a command window, type ipconfig /all, and then press Enter.
b. Note your PC interfaces IP address and MAC (physical) address.
c.
Ask a team member for their PCs IP address and provide your PCs IP address to them. Do not provide
them with your MAC address at this time.
Note: Clicking the first interface icon in the row of icons also opens the Interface List.
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On the Wireshark: Capture Interfaces window, click the check box next to the interface connected to your
LAN.
Note: If multiple interfaces are listed and you are unsure which interface to check, click the Details
button, and then click the 802.3 (Ethernet) tab. Verify that the MAC address matches what you noted in
Step 1b. Close the Interface Details window after verifying the correct interface.
d. After you have checked the correct interface, click Start to start the data capture.
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Information will start scrolling down the top section in Wireshark. The data lines will appear in different
colors based on protocol.
e. This information can scroll by very quickly depending on what communication is taking place between
your PC and the LAN. We can apply a filter to make it easier to view and work with the data that is being
captured by Wireshark. For this lab, we are only interested in displaying ICMP (ping) PDUs. Type icmp in
the Filter box at the top of Wireshark and press Enter or click on the Apply button to view only ICMP
(ping) PDUs.
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f.
This filter causes all data in the top window to disappear, but you are still capturing the traffic on the
interface. Bring up the command prompt window that you opened earlier and ping the IP address that you
received from your team member. Notice that you start seeing data appear in the top window of
Wireshark again.
Note: If your team members PC does not reply to your pings, this may be because their PC firewall is
blocking these requests. Please see Appendix A: Allowing ICMP Traffic Through a Firewall for
information on how to allow ICMP traffic through the firewall using Windows 7.
g. Stop capturing data by clicking the Stop Capture icon.
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a. Click the first ICMP request PDU frames in the top section of Wireshark. Notice that the Source column
has your PCs IP address, and the Destination contains the IP address of the teammates PC you pinged.
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b. With this PDU frame still selected in the top section, navigate to the middle section. Click the plus sign to
the left of the Ethernet II row to view the Destination and Source MAC addresses.
Does the Source MAC address match your PCs interface? ______
Does the Destination MAC address in Wireshark match the MAC address that of your team members?
_____
How is the MAC address of the pinged PC obtained by your PC?
___________________________________________________________________________________
Note: In the preceding example of a captured ICMP request, ICMP data is encapsulated inside an IPv4
packet PDU (IPv4 header) which is then encapsulated in an Ethernet II frame PDU (Ethernet II header)
for transmission on the LAN.
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b. Make sure the check box next to the LAN interface is checked, and then click Start.
c.
A window prompts to save the previously captured data before starting another capture. It is not
necessary to save this data. Click Continue without Saving.
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d. With the capture active, ping the following three website URLs:
1) www.yahoo.com
2) www.cisco.com
3) www.google.com
Note: When you ping the URLs listed, notice that the Domain Name Server (DNS) translates the URL to
an IP address. Note the IP address received for each URL.
e. You can stop capturing data by clicking the Stop Capture icon.
Step 2: Examining and analyzing the data from the remote hosts.
a. Review the captured data in Wireshark, examine the IP and MAC addresses of the three locations that
you pinged. List the destination IP and MAC addresses for all three locations in the space provided.
1st Location:
nd
rd
2 Location:
3 Location:
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How does this information differ from the local ping information you received in Part 2?
____________________________________________________________________________________
____________________________________________________________________________________
Reflection
Why does Wireshark show the actual MAC address of the local hosts, but not the actual MAC address for the
remote hosts?
_______________________________________________________________________________________
_______________________________________________________________________________________
Step 1: Create a new inbound rule allowing ICMP traffic through the firewall.
d. From the Control Panel, click the System and Security option.
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In the left pane of the Windows Firewall window, click Advanced settings.
g. On the Advanced Security window, choose the Inbound Rules option on the left sidebar and then click
New Rule on the right sidebar.
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h. This launches the New Inbound Rule wizard. On the Rule Type screen, click the Custom radio button and
click Next
i.
In the left pane, click the Protocol and Ports option and using the Protocol type drop-down menu, select
ICMPv4, and then click Next.
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j.
In the left pane, click the Name option and in the Name field, type Allow ICMP Requests. Click Finish.
This new rule should allow your team members to receive ping replies from your PC.
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b. To disable the rule, click the Disable Rule option. When you choose this option, you will see this option
change to Enable Rule. You can toggle back and forth between Disable Rule and Enable Rule; the status
of the rule also shows in the Enabled column of the Inbound Rules list.
c.
To permanently delete the ICMP rule, click Delete. If you choose this option, you must re-create the rule
again to allow ICMP replies.
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