Wireshark

Special Thanks: This article was made possible by support from Linux Professional Institute

Wireshark is an essential system administrator and security tool for any network. That broad statement covers a lot of ground, but it is true nonetheless. Even on the Wireshark website, the About page refers to it as “the world’s foremost and widely-used network protocol analyzer.” It began life in 1998 with the name Ethereal, but the authors had to change it a few years later due to a trademark problem for the original author, Gerald Combs. Wireshark is cross-platform, free, and open source.

Understanding Wireshark

Wireshark is a network protocol analyzer -- sometimes referred to as a packet analyzer or as a network sniffer (see the “Caution” box). It offers live network packet capture and offline analysis. If you’ve ever used Wireshark, or any network sniffer, you know that it only takes a few minutes to capture thousands of packets. For this reason, Wireshark has a very powerful display filter, which you’ll learn to love, because who really needs to see thousands of “Who has” Address Resolution Protocol (ARP) messages, unless that’s what you’re looking for in a capture?

So what does one find when “sniffing” the network? In other words, what can you do with Wireshark? I’ve seen many lists that attempt to show Wireshark’s many facets, and here’s another one:

• Find network communications sent in clear text.
• Find evidence of attacks or probes.
• Discover clandestine or forbidden applications.
• Read captures from other programs, such as tcpdump.
• Take snapshots of traffic during peak periods.
• Establish a baseline of “normal” network traffic.
• Capture traffic to or from specific hosts.
• Look at attempts to connect to your wireless networks.

There are many other tasks one can perform with Wireshark, but these are the ones most often listed by legitimate users (see the “Hackers Beware” box).

A final word on what Wireshark is not. It is not a security information and event management (SIEM) suite nor should it be “sold” to management as such. It is no substitute for a SIEM, although its data can be used for some of the same activities, such as event correlation and forensic packet analysis.

Wireshark is a powerful tool that should be part of a system or security administrator’s arsenal of tools. However, be cautious of relying too heavily on any single tool for complete analysis. Such reliance reminds me of the Indian parable of the blind men and the elephant, where each man experiences a different part of the elephant and makes assumptions about the entire animal based on limited information. Gather as much information about an incident and network behavior as possible with different tools and from different perspectives.

Installing Wireshark

The first thing you need to do is install Wireshark. For Red Hat Linux-based systems, installing is easy with:

sudo yum –y install wireshark-gnome

Yes, I suggest that you install the graphical version. You can install the command-line-only version with:

sudo yum –y install Wireshark

You actually get the command-line version when you install the wireshark-gnome package. You also download and install any dependencies, which is usually just the libsmi package but could vary depending on your personal installation.

For Debian-based systems, use:

sudo apt install wireshark

This command installs both the command-line version and the graphical version.

If your system can’t find Wireshark, use these commands and try again:

sudo add-apt-repository ppa:wireshark-dev/stablesudo apt-get update

Up and Running

Now that you have Wireshark installed, it’s time to launch it and grab some network traffic. Although Wireshark’s installation program provides you with a handy program link under Applications | Internet, don’t use it unless you’re logged in as root. Open a Terminal window and enter:

sudo wireshark &

Wireshark should launch and look similar to Figure 1.

Figure 1: The Wireshark graphical interface.

I know you want to get right to it, so click Capture on the menubar and select Interfaces from the dropdown list as shown in Figure 2.

Figure 2: Select Interfaces from the Capture menu option.

The first step in capturing packets is to set up listening interfaces.

Note: You must either run Wireshark as root or use sudo to run it. There are ways around this, but for simplicity, run it with elevated privileges. You can run Wireshark as a regular user, but you won’t be able to capture traffic.

Figure 3 displays a list of local interfaces. Select those appropriate for your network.

Figure 3: Selecting the wired interface enp0s3 for packet capture.

Click Start to begin capturing network packets on your selected network interface. Figure 4 shows a capture in progress.

Figure 4: Watching Wireshark sniff network packets.

Figure 5 shows a system being scanned by a port scanner (we will look at this again later).

Figure 5: A Wireshark capture in progress showing a port scan.

And finally, Figure 6 is a demonstration of a ping flood.

Figure 6: A Wireshark capture demonstrating a ping flood in progress.