In any packet-switched network, packets represent units of data that are transmitted between computers. It is the responsibility of network engineers and system administrators alike to monitor and inspect the packets for security and troubleshooting purposes.
To do this, they rely on software programs called network packet analyzers, with Wireshark perhaps being the most popular and used due to its versatility and easiness of use. On top of this, Wireshark allows you to not only monitor traffic in real-time, but also to save it to a file for later inspection.
In this article we will share 10 tips on how to use Wireshark to analyze packets in your network, and hope that when you reach the Summary section you will feel inclined to add it to your bookmarks.
Installing Wireshark in Linux
To install Wireshark, select the right installer for your operating system / architecture from https://www.wireshark.org/download.html.
Particularly, if you are using Linux, Wireshark must be available directly from your distribution’s repositories for an easier install at your convenience. Although versions may differ, the options and menus should be similar – if not identical in each one.
------------ On Debian/Ubuntu based Distros ------------ $ sudo apt-get install wireshark ------------ On CentOS/RHEL based Distros ------------ $ sudo yum install wireshark ------------ On Fedora 22+ Releases ------------ $ sudo dnf install wireshark
There is a known bug in Debian and derivatives that may prevent listing the network interfaces unless you use sudo to launch Wireshark. To fix this, follow the accepted answer in this post.
Once Wireshark is running, you can select the network interface that you want to monitor under Capture:
Wireshark Network Analyzer
In this article we will use eth0, but you can choose another one if you wish. Don’t click on the interface yet – we will do so later once we have reviewed a few capture options.
Setting Capture Options
The most useful capture options we will consider are:
- Network interface – As we explained before, we will only analyze packets coming through eth0, either incoming or outcoming.
- Capture filter – This option allows us to indicate what kind of traffic we want to monitor by port, protocol, or type.
Before we proceed with the tips, it is important to note that some organizations forbid the use of Wireshark in their networks. That said, if you are not utilizing Wireshark for personal purposes make sure your organization allows its use.
For the time being, just select eth0 from the dropdown list and click Start at the button. You will start seeing all traffic passing through that interface. Not really useful for monitoring purposes due to the high amount of packets inspected, but it’s a start.
Monitor Network Interface Traffic
In the above image we can also see the icons to list the available interfaces, to stop the current capture, and to restart it (red box on the left) and to configure and edit a filter (red box on the right). When you hover over one of these icons, a tooltip will be displayed to indicate what it does.
We will begin by illustrating capture options, whereas tips #7 through #10 will discuss how to do actually do something useful with a capture.
TIP #1 – Inspect HTTP Traffic
Type http in the filter box and click Apply. Launch your browser and go to any site you wish:
Inspect HTTP Network Traffic
To begin every subsequent tip, stop the live capture and edit the capture filter.
TIP #2 – Inspect HTTP Traffic from a Given IP Address
In this particular tip, we will prepend ip==192.168.0.10&& to the filter stanza to monitor HTTP traffic between the local computer and 192.168.0.10:
Inspect HTTP Traffic on IP Address
TIP #3 – Inspect HTTP Traffic to a Given IP Address
Closely related with #2, in this case we will use ip.dst as part of the capture filter as follows:
ip.dst==192.168.0.10&&http
Monitor HTTP Network Traffic to IP Address
To combine tips #2 and #3, you can use ip.addr in the filter rule instead of ip.src or ip.dst.
TIP #4 – Monitor Apache and MySQL Network Traffic
Sometimes you will be interested in inspecting traffic that matches either (or both) conditions whatsoever. For example, to monitor traffic on TCP ports 80 (web server) and 3306 (MySQL / MariaDB database server), you can use an OR condition in the capture filter:
tcp.port==80||tcp.port==3306
Monitor Apache and MySQL Traffic
In tips #2 and #3, || and the word or produce the same results. Same with && and the word and.
TIP #5 – Reject Packets to Given IP Address
To exclude packets not matching the filter rule, use ! and enclose the rule within parentheses. For example, to exclude packages originating from or being directed to a given IP address, you can use:
!(ip.addr == 192.168.0.10)
TIP #6 – Monitor Local Network Traffic (192.168.0.0/24)
The following filter rule will display only local traffic and exclude packets going to and coming from the Internet:
ip.src==192.168.0.0/24 and ip.dst==192.168.0.0/24
Monitor Local Network Traffic
TIP #7 – Monitor the Contents of a TCP Conversation
To inspect the contents of a TCP conversation (data exchange), right click on a given packet and choose Follow TCP stream. A window will pop-up with the content of the conversation.
This will include HTTP headers if we are inspecting web traffic, and also any plain text credentials transmitted during the process, if any.
Monitor TCP Conversation
TIP #8 – Edit Coloring Rules
By now I am sure you already noticed that each row in the capture window is colored. By default, HTTP traffic appears in green background with black text, whereas checksum errors are shown in red text with black background.
If you wish to change these settings, click the Edit coloring rules icon, choose a given filter and click Edit.
Customize Wireshark Output in Colors
TIP #9 – Save the Capture to a File
Saving the contents of a capture will allow us to be able to inspect it with greater detail. To do this, go to File → Export and choose an export format from the list:
Save Wireshark Capture to File
TIP #10 – Practice with Capture Samples
If you think your network is “boring”, Wireshark provides a series of sample capture files that you can use to practice and learn. You can download these SampleCaptures and import them via the File → Import menu.
Summary
Wireshark is free and open source software, as you can see in the FAQs section of the official website. You can configure a capture filter either before or after starting an inspection.
In case you didn’t notice, the filter has an autocomplete feature that allows you to easily search for the most used options that you can customize later. With that, the sky is the limit!