Network operators will find an improvement with Wi-Fi 6/6E in how access points broadcast SSIDs. We won’t be getting away from environments that have several broadcasted SSIDs (ahem.. WeWork).
An environment surrounded by many Wi-Fi networks will be affected by beacon overhead. It will eat away at airtime due to the amount of SSIDs broadcasted. Multiple BSSID is mandatory in Wi-Fi 6. This will minimize the beacon overhead.
What is Multiple BSSID
Multiple BSSID is the advertisement of colocated SSIDs in a single beacon or probe response frame. The multiple SSIDs will correspond to a single SSID.
Prior to Wi-Fi 6/6E, multiple SSIDs from an access point would be broadcasted by its own individual BSSID. We’ve been told to keep broadcasted SSIDs to a maximum of three due to beacon overhead.
Airtime from multiple BSSIDs will contribute to airtime utilization resulting in wasted capacity and low efficiency.
I love how we bring existing methods into newer protocols many years later. Multiple BSSID was first defined in 802.11v-2011. 10 years later we’re now making it mandatory to use.
Where can you find Multiple BSSID
You’ll find the Multiple BSSID information from within the beacon and probe response frame. I’ve included a Wireshark capture from my test AP where I’ve configured 4 different SSIDs – Test-Net, Frame Thrower, Slurp Fish, and Banter.
There are two types of Multiple BSSIDs:
In my capture, you’ll see one SSID in the beacon frame: Test-Net. That SSID is the Transmitted BSSID. The remaining SSIDs configured on the AP are Non-Transmitted BSSID.
Capturing Wi-Fi 6/6E
Within the frame capture, you’ll find another element – Multiple BSSID. This element contains the info we need to identify all the SSIDs being broadcasted. Inside of the subelement are the non-transmitted BSSIDs and their information.
The Multiple BSSID element contains useful information:
Max BSSID Indicator – Carries number of active BSSIDs in the multiple BSSID set
Nontransmitted BSSID Profile – One for each of the non-transmitted BSSIDs containing their information
Within the Nontransmitted BSSID Profile you’ll find all the capabilities for the additional SSIDs. Devices need to know what’s required to join these SSIDs.
How to capture Multiple BSSID
You can find these details in a few ways. You can do a frame capture and open the pcap inside of Wireshark just as I’ve shown above. You’ll need a Wi-Fi 6 capable device.
Using WiFi Explorer you can find these exact same details without needing to do a frame capture. You’ll need a Wi-Fi 6 capable device or capture file to import. Import my frame capture (linked below) into WiFi Explorer.
I’ve also used the EtherScope nXG to visualize Multiple BSSID. They indicate Transmitted and Non-Transmitted BSSID with specific icons and provide the capability to drill in further as shown in the screenshots below.