Colorful Ethernet cables.
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Wireshark is the de facto standard for analyzing network traffic. Unfortunately, it does become increasingly laggy as the packet capture grows. Brim solves this problem so well, it’ll change your Wireshark workflow.

Wireshark Is Great, But . . .

Wireshark is a wonderful piece of open-source software. It’s used by amateurs and professionals alike worldwide to investigate networking issues. It captures the data packets that travel down the wires or through the ether of your network. Once you’ve captured your traffic, Wireshark allows you to filter and search through the data, trace conversations between network devices, and much more.

As great as Wireshark is, though, it does have one issue. Network data capture files (called network traces or packet captures), can get very large, very quickly. This is especially true if the issue you’re trying to investigate is complex or sporadic, or the network is large and busy.

The larger the packet capture (or PCAP), the more laggy Wireshark becomes. Just opening and loading a very large (anything over 1 GB) trace can take so long, you’d think Wireshark had keeled over and given up the ghost.

Working with files of that size is a real pain. Every time you perform a search or change a filter, you have to wait for the effects to be applied to the data and updated on the screen. Each delay disrupts your concentration, which can hinder your progress.

Brim is the remedy for these woes. It acts as an interactive preprocessor and front-end for Wireshark. When you want to see the granular level Wireshark can provide, Brim instantly opens it for you exactly on those packets.

If you do a lot of network capture and packet analysis, Brim will revolutionize your workflow.

RELATED: How to Use Wireshark Filters on Linux

Installing Brim

Brim is very new, so it hasn’t yet made its way into the software repositories of the Linux distributions. However, on the Brim download page, you’ll find DEB and RPM package files, so installing it on Ubuntu or Fedora is simple enough.

If you use another distribution, you can download the source code from GitHub and build the application yourself.

Brim uses zq, a command-line tool for Zeek logs, so you’ll also need to download a ZIP file containing the zq binaries.

Installing Brim on Ubuntu

If you’re using Ubuntu, you’ll need to download the DEB package file and zq Linux ZIP file. Double-click the downloaded DEB package file, and the Ubuntu Software application will open. The Brim license is mistakenly listed as “Proprietary”—it uses the BSD 3-Clause License.

Click “Install.”

Click "Install."

When the installation is complete, double-click the zq ZIP file to launch the Archive Manager application. The ZIP file will contain a single directory; drag and drop it from the “Archive Manager” to a location on your computer, like the “Downloads” directory.

We type the following to create a location for the zq binaries:

sudo mkdir /opt/zeek

sudo mkdir /opt/zeek in a terminal window.

We need to copy the binaries from the extracted directory to the location we just created. Substitute the path and name of the extracted directory on your machine in the following command:

sudo cp Downloads/zq-v0.20.0.linux-amd64/* /opt/Zeek

sudo cp Downloads/zq-v0.20.0.linux-amd64/* /opt/Zeek in a terminal window.

We need to add that location to the path, so we’ll edit the BASHRC file:

sudo gedit .bashrc

sudo gedit .bashrc in a terminal window.

The gedit editor will open. Scroll to the bottom of the file, and then type this line:

export PATH=$PATH:/opt/zeek

The BASHRC file in the gedit editor with the line export PATH=$PATH:/opt/zeek.

Save your changes and close the editor.

Installing Brim on Fedora

To install Brim on Fedora, download the RPM package file (instead of the DEB), and then follow the same steps we covered for the Ubuntu installation above.

Interestingly, when the RPM file opens in Fedora, it’s correctly identified as having an open-source license, rather than a proprietary one.

Launching Brim

Click “Show Applications” in the dock or press Super+A. Type “brim” in the Search box, and then click “Brim” when it appears.

Type "brim" in the Search box.

Brim launches and displays its main window. You can click “Choose Files” to open a file browser, or drag and drop a PCAP file in the area surrounded by the red rectangle.

The Brim main window after startup.

Brim uses a tabbed display, and you can have multiple tabs open simultaneously. To open a new tab, click the plus sign (+) at the top, and then select another PCAP.

Brim Basics

Brim loads and indexes the selected file. The index is one of the reasons Brim is so fast. The main window contains a histogram of packet volumes over time, and a list of network “flows.”

The Brim main window with a PCAP file loaded.

A PCAP file holds a time-ordered stream of network packets for a great many network connections. The data packets for the various connections are intermingled because some of them will have been opened concurrently. The packets for each network “conversation” are interspersed with the packets of other conversations.

Wireshark displays the network stream packet by packet, while Brim uses a concept called “flows.” A flow is a complete network interchange (or conversation) between two devices. Each flow type is categorized, color coded, and labeled by flow type. You’ll see flows labeled “dns,” “ssh,” “https,” “ssl,” and many more.

If you scroll the flow summary display left or right, many more columns will be displayed. You can also adjust the time period to display the subset of information you want to see. Below are a few ways you can view data:

  • Click a bar in the histogram to zoom in on the network activity within it.
  • Click and drag to highlight a range of the histogram display and zoom in. Brim will then display the data from the highlighted section.
  • You can also specify exact periods in the “Date” and “Time” fields.

Brim can display two side panes: one on the left, and one on the right. These can be hidden or remain visible. The pane on the left shows a search history and list of open PCAPs, called spaces. Press Ctrl+[ to toggle the left pane on or off.

The "Spaces" pane in Brim.

The pane on the right contains detailed information about the highlighted flow. Press Ctrl+] to toggle the right pane on or off.

A highlighted "Fields" pane on Brim.

Click “Conn” in the “UID Correlation” list to open a connection diagram for the highlighted flow.

Click "Conn."

In the main window, you can also highlight a flow, and then click the Wireshark icon. This launches Wireshark with the packets for the highlighted flow displayed.

Click the Wireshark icon in the Brim main window.

Wireshark opens, displaying the packets of interest.

Packets selected from Brim displayed in Wireshark.

Filtering in Brim

Searching and filtering in Brim are flexible and comprehensive, but you don’t have to learn a new filtering language if you don’t want to. You can build a syntactically correct filter in Brim by clicking fields in the summary window, and then selecting options from a menu.

For example, in the image below, we right-clicked a “dns” field. We’re then going to select “Filter = Value” from the context menu.

A context menu in the summary window.

The following things then occur:

  • The text _path = "dns" is added to the search bar.
  • That filter is applied to the PCAP file, so it will only display flows that are Domain Name Service (DNS) flows.
  • The filter text is also added to the search history in the left pane.

A summary screen filtered by DNS.

We can add further clauses to the search term using the same technique. We’ll right-click the IP address field (containing “192.168.1.26”) in the “Id.orig_h” column, and then select “Filter = Value” from the context menu.

This adds the additional clause as an AND clause. The display is now filtered to show DNS flows that originated from that IP address (192.168.1.26).

A summary screen filtered by flow type and IP address.

The new filter term is added to the search history in the left pane. You can hop between searches by clicking the items in the search history list.

The destination IP address for most of our filtered data is 81.139.56.100. To see which DNS flows were sent to different IP addresses, we right-click “81.139.56.100” in the “Id_resp_h” column, and then select “Filter != Value” from the context menu.

Summary screen with a search filter containing an "!=" clause.

Only one DNS flow that originated from 192.168.1.26 wasn’t sent to 81.139.56.100, and we’ve located it without having to type anything to create our filter.

Pinning Filter Clauses

When we right-click an “HTTP” flow and select “Filter = Value” from the context menu, the summary pane will display only HTTP flows. We can then click the Pin icon next to the HTTP filter clause.

Click the Pin icon.

The HTTP clause is now pinned in place, and any other filters or search terms we use will be executed with the HTTP clause prepended to them.

If we type “GET” in the search bar, the search will be restricted to flows that have already been filtered by the pinned clause. You can pin as many filter clauses as necessary.

"GET" in the Search box.

To search for POST packets in the HTTP flows, we simply clear the search bar, type “POST,” and then press Enter.

"POST" in the Search box executed with the pinned "HTTP" clause.

Scrolling sideways reveals the ID of the remote host.

The remote "Host" column in the Brim summary screen.

All the search and filter terms are added to the “History” list. To reapply any filter, just click it.

The auto-populated "History" list.

You can also search for a remote host by name.

Searching for "trustwave.com" in Brim.

Editing Search Terms

If you want to search for something, but don’t see a flow of that type, you can click any flow and edit the entry in the search bar.

For example, we know there must be at least one SSH flow in the PCAP file because we used rsync to send some files to another computer, but we can’t see it.

So, we’ll right-click another flow, select “Filter = Value” from the context menu, and then edit the search bar to say “ssh” instead of “dns.”

We press Enter to search for SSH flows and find there’s only one.

An SSH flow in the summary window.

Pressing Ctrl+] opens the right pane, which shows the details for this flow. If a file was transferred during a flow, the MD5, SHA1, and SHA256 hashes appear.

Right-click any of these, and then select “VirusTotal Lookup” from the context menu to open your browser at the VirusTotal website and pass in the hash for checking.

VirusTotal stores the hashes of known malware and other malicious files. If you’re unsure whether a file is safe, this is an easy way to check, even if you no longer have access to the file.

The hash context menu options.

If the file is benign, you’ll see the screen shown in the image below.

A "No Matches Found" response from the VirusTotal site.

The Perfect Complement to Wireshark

Brim makes working with Wireshark even faster and easier by allowing you to work with very large packet capture files. Give it a test run today!

Dave McKay Dave McKay
Dave McKay first used computers when punched paper tape was in vogue, and he has been programming ever since. After over 30 years in the IT industry, he is now a full-time technology journalist. During his career, he has worked as a freelance programmer, manager of an international software development team, an IT services project manager, and, most recently, as a Data Protection Officer. Dave is a Linux evangelist and open source advocate.
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