mojo packets

CTS 121: Capturing Wireless Frames with a Mac

Capturing wireless frames is a must know skill for any Wi-Fi network engineer.

Capturing Wireless Frames with a Mac

The Macbook Pro is an excellent tool for capturing wireless frames. The built-in wireless adapter can be used to sniff wireless frames in the air. As I like to say, the best troubleshooting tool you can have is the one that’s with you. Since I have my Mac with me all the time I tend to capture frames wherever I go.

There are many pros with capturing frames. It’s a great way to learn how Wi-Fi works. This is how I got started. Understanding how Wi-Fi communication works through frame captures gives you an upper-hand. One example is learning about the 802.11 State Machine.

When it comes to troubleshooting complicated issues, frames don’t lie. Not too long ago, my laptop had a difficult time connecting to public Wi-Fi. It frustrated me so much I decided to capture some frames. Within minutes I found out why. Just take a look at the screenshot below.

Frame capture of an association response

Tools

How To Capture Frames

  1. Install Wireshark
  2. Install the Metageek Profile
    1. Unzip the file
    2. Copy directory to /Users/user/.config/wireshark/profiles/
    3. Enable the profile in Wireshark by clicking on the bottom right of the open application. See screenshot below.
  3. Install Airtool
  4. Select channel & channel width to capture on
    1. Capturing frames with Airtool
  5. Start the capture and stop after a short time
  6. Analyze with Wireshark or Mojo Packets

Links and Resources

CTS 102: Capturing Wireless Frames

François and Rowell discuss their experiences capturing wireless frames for analysis and what tools they used to do it.

This episode is sponsored by Metageek

Sponsored by Metageek

Capturing Wireless Frames

It’s one of my favorite things to do. Capture wireless frames anywhere there’s a wireless network present. I know. I’m a boring guy. But I can’t help taking a look. In this episode on capturing wireless frames, we go over our favorite tools and apps which help us solve real world problems.

Why should you capture frames? If you want to learn how wireless works, then you need to start diving into frames. That’s how you’ll learn exactly what you need to know by seeing how it works. It’s perfect for learning any of the CWNP certifications and especially for the CWAP. By looking at wireless frames, you’ll begin seeing how wireless devices and access points talk to each other and acquire the shared medium.

A beacon frame displayed from Wireshark.

A sample beacon frame from Wireshark

Another reason for capturing wireless frames is to perform analysis. There may be an issue that’s hard to solve and requires wireless frame analysis. This could be as simple as finding out a device does not negotiate the same parameters as the BSS. Or maybe you’re trying to find out what could be slowing down wireless for every other device.

It’s the old saying, packets never lie. But in this case, frames never lie!

Screenshot from Metageek Eye P.A.

An example of using Metageek Eye P.A.

You can capture wireless frames on any platform such as MacOS, Windows, and Linux. When it comes to the platform of choice, we prefer to use MacOS. By default, you can place the MacOS wireless adapter in promiscuous mode. This mode is used to capture all frames, even those not destined to the host. By utilizing an app such as Airtool, it’s possible to fine tune a frame capture down to parameters such as the channel, channel width, payload or no payload, etc.

Then with Wireshark, the analysis can be performed.

Mojo Packets Analysis

A section of Mojo Packets analysis.

In the episode, François and I speak about our experiences in using frame analysis. I bring up a situation where Skype calls kept dropping but the issue was really a consumer level device trying to take up most of the airtime. There are other examples also described in the episode.

Here are some screenshots of different applications of frame capture and analysis.

Links and Resources