Band Select, MAC address randomization and Probe Response

[_Gustavo_]

Hello everybody,

I have some questions about Band Select, MAC address randomization and Probe Request/Response. Please, feel free to contribute and add your own questions to this discussion.

1) How is Band Select feature impacted by MAC address randomization?

2) How often a client randomizes its MAC address? Is there a timeout or it happens on every Probe Request?

3) Are Probe Requests randomized between 2.4Ghz and 5Ghz bands independently?

4) Is there a way to rate limit Probe Responses on a 5508 WLC? Maybe just set a limit of Probe Responses based on a threshold RSSI of the client's Probe Request.

Thank you for your responses.

[patoberli]

This depends on the used client and operating system.
Most clients don't change their MAC address, once they are connected with a network. They only use a random MAC for scanning and searching for SSIDs with hidden BSSID. Once they connect and the user enters the PSK (or other credentials) the clients use their real hardware MAC and not change it.
I hope this answer helps you.

[_Gustavo_]

Hi,

As far as I understood Band Select works at the association phase. So the client is probing for SSIDs in 2.4Ghz and 5Ghz bands when Band Select takes place. It works by delaying probe responses in 2.4Ghz bands if the same MAC is heard probing the 5Ghz band. The client is not connected/associated to any SSID at this moment and is able to randomize its MAC address. Could this scenario interfere with Band Select, eventually making it useless for dual band clients that randomize their MAC address?

Thanks.

[Scott Fella]

I don’t think so. It would be a good test to see. The Mac can’t change during the authentication phase as that is what the controller will use to put that device on the network.

[_Gustavo_]

Sorry for the miss understanding. The whole process seems to be executed before authentication phase. The client uses probe requests to build a list of available SSIDs and Band Select tries to hide 2.4Ghz SSIDs from dual band clients.

[Scott Fella]

That is correct, during the association phase.