This post is directly related to the following previous article: "Wireshark: How to check it a Wi-Fi Network Supports 802.11v".

In the previous article, we talked about how to check if a specific Wi-Fi network is supporting IEEE 802.11v, from the access point perspective. Like anything in Wi-Fi, we need support from both the access point and the STAs in order for it to work.

So in this article, we are going to explain how we can validate is a specific client device supports 802.11v.

I would like to address special thanks to Phil Morgan for providing useful information and giving me the idea to write this follow up post.

We were checking the Beacon frame broadcasted by the AP in order to validate if a specific SSID was supporting 802.11v. In order to check if a specific client supports it, we need to take a look at the Association Request frame sent by the client device when it connects to the Wi-Fi network. (cf. diagram below)

Note: before we start looking deeper into the association request frame, something important needs to be noted regarding 802.11v client support. Since the support of 802.11v is advertised by the AP in the beacon frames the station will be aware of 802.11v support within the BSS and will only advertise its support for 802.11v in its association request if it is advertised by the AP in the beacon frame.
So if you are performing your own packet captures, make sure you enable 802.11v support on the access point first.

Once again, looking at the association request frame in order to find 802.11v support, we need to focus on the Extended Capabilities Information Element number 127 and look at the 4th bit of the 3rd octet. This bit is most commonly named the "BSS Transition bit". If the bit is set to "1", the client device support 802.11v.

The following screenshot shows the BSS Transition bit of an association request sent by a Samsung Galaxy S7 Edge. This is taken from the .pcap files available on Mike Albano's website.

Mike Albano did a really good job studying the most common Wi-Fi client devices. He documented his work on his website called clients.mikealbano.com. I'm talking about his website because there is an option to filter only the devices supporting 802.11v.

Make sure to read the note at the bottom of the page related to IEEE 802.11v support.

So if you are not sure if a specific client supports 802.11v, you can head over to his website and perform a quick research. You can even download a .pcap file for every device containing an association request.

On a Cisco Wireless LAN Controller, there is a way to check if an associated client supports IEEE 802.11v. Obviously, as explained earlier, this client device has to be associated to an SSID already advertising the BSS transition capability.

So once the client is associated to the Wi-Fi, head over to the "Monitor" page, on the left menu, select "Clients".  This will open up a new page displaying all the client devices connected to your different Wi-Fi networks supported by the controller.
Click on the mac address of the client that you want to study. This will open up a new page providing more detailed information related to this specific client.
​On this page, you will be able to see if it support IEEE 802.11v, as shown below, under the "802.11v BSS Transition" sub-section:

If the client device supports it, you will see "Supported", if it doesn't, you will see "Not Supported".


Thank you for reading!

Cheers'


​
written by François Vergès

Today's exercice is simple: study the beacon frame and try to figure out what characteristics of the Wi-Fi network are advertised.

In this first article, we will be talking about 802.11v.

Looking at a Beacon frame in order to find 802.11v support, we need to focus on the Extended Capabilities Information Element number 127 and look at the 4th bit of the 3rd octet. This bit is most commonly named the "BSS Transition bit".

Below is a look at a Beacon of a Wi-Fi network not supporting 802.11v. As you can see, the BSS Transition bit is set to "0".

Now, we are going to enable 802.11v support on this same SSID.

In order to enable 802.11v on a WLAN profile on a Cisco WLC, you need to

• Navigate to the "WLAN" menu
  
• Select the WLAN profile you want to modify in order to open up the configuration view
  
• In the configuration view, select the "Advanced" tab
  
• Finally, in the advanced tab, under the "11v BSS Transition Support" section, select the "BSS Transition" option as shown in the image bellow:

You can now apply and save your new configurations.

Once the configurations have been applied and that the APs start broadcasting the new beacon frames, you are now able to see that the BSS Transition bit has been set to "1".

Thank you for reading. In the next post, we will explain how to check if a Wi-Fi network is supporting 802.11k.

If you want to optimize the way you use Wireshark to perform Wi-Fi analysis, head over to this post: www.semfionetworks.com/blog/wireshark-most-common-80211-filters

Cheers'

​
written by François Vergès