band steering

Band steering is a feature of accepting the connection over the preferred band. In most of the cases, we would like dual-band mobile clients to associate with interference-less band which is 5GHz, instead of 2.4 GHz. The feature isn’t defined in any 802.11 standards, it is rather proprietary feature implemented in most of the enterprise Wi-Fi vendors.

The example is from my lab connecting a mobile client (CC-44-63-1B-2D-FA) to the AP – SSID 2. I have added also a syslog output of the Extreme WING wireless controllers to show how the proprietary process works.

The configuration is easy on Extreme WING:

WLC(config)#wlan 2
WLC(config-wlan-2)#client-load-balancing
...
WLC(config-device-84-24-8D-89-16-18)#load-balancing balance-band-loads
WLC(config-device-84-24-8D-89-16-18)#commit

 

The client sends a probe request for SSID 2 on channel 6:

1

There is no probe responses sent from the AP.

As the mobile client tries to join the SSID on channel 6. It sends an authentication request, the AP responses with authentication response, the mobile client sends an association request:

2

The same output from the wireless controller’s syslog:

[AP2] 16:20:52.950: mgmt:rx auth-req from CC-44-63-1B-2D-FA on radio 0 (mgmt.c:3940)
[AP2] 16:20:52.950: mgmt:tx auth-rsp to CC-44-63-1B-2D-FA on radio 0. status: success (mgmt.c:1314)
[AP2] 16:20:52.955: mgmt:rx association-req from CC-44-63-1B-2D-FA on radio AP2:R1 signal-strength is -46dBm (mgmt.c:3921)
[AP2] 16:20:52.955: client:MU supports 802.11v bss transition CC-44-63-1B-2D-FA (mgmt.c:2762)
[AP2] 16:20:52.955: client:MU CC-44-63-1B-2D-FA panBU enab_cap=00 00 00 00, supp_cap=00 00 00 00 (mgmt.c:3128)
[AP2] 16:20:52.955: client:using cached vlan 4 for wireless client CC-44-63-1B-2D-FA (mgmt.c:3372)
[AP2] 16:20:52.955: mgmt:CC-44-63-1B-2D-FA ignoring association req on wlan [2], radio 0, BAND-STEERING:2.4GHz overloaded (mgmt.c:33

The last entry provided information that association request has been ignored due to band steering enabled.

We will see 4 more retries, every 300msec:

3

Each time the AP ignores the association request on 2.4 GHz, the same output occurs 4 x times:

[AP2] 16:20:54.340: mgmt:rx auth-req from CC-44-63-1B-2D-FA on radio 0 (mgmt.c:3940)
[AP2] 16:20:54.340: mgmt:tx auth-rsp to CC-44-63-1B-2D-FA on radio 0. status: success (mgmt.c:1314)
[AP2] 16:20:54.347: mgmt:rx association-req from CC-44-63-1B-2D-FA on radio AP2:R1 signal-strength is -45dBm (mgmt.c:3921)
[AP2] 16:20:54.347: client:MU supports 802.11v bss transition CC-44-63-1B-2D-FA (mgmt.c:2762)
[AP2] 16:20:54.347: client:MU CC-44-63-1B-2D-FA panBU enab_cap=00 00 00 00, supp_cap=00 00 00 00 (mgmt.c:3128)
[AP2] 16:20:54.347: client:using cached vlan 4 for wireless client CC-44-63-1B-2D-FA (mgmt.c:3372)
[AP2] 16:20:53.347: mgmt:CC-44-63-1B-2D-FA ignoring association req on wlan [2], radio 0, BAND-STEERING:2.4GHz overloaded (mgmt.c:33

 

After 5th attempt the mobile client gives up and join the 5GHz SSID on channel 44:

4.PNG

Band steering is an interesting feature for implementation in every dual-band WLAN network, however I have seen in my lab and in production networks that 2.4 GHz and 5GHz coverage areas should be similar for the feature to work efficiently.

When the 5GHz WLAN network’s signal was weaker by -10dBm comparing to 2.4GHz WLAN network in my lab (the same power for 2.4 GHz and 5GHz radios), the mobile client Apple iPhone didn’t even try to associate to 5GHz radio.

 

 

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