Cisco Band-Select Feature

In this post we will learn about this feature. Today I faced a problem while a client was continuously trying to connect to 2.4 GHz even though the traffic was full congested/fully loaded/Full with interferences. Then I thought, is it a way to force dual band clients (Which support both frequency range 2.4GHz and 5 GHz) to connect with 5 GHz radio and tried to find out cisco docs or tech-notes and finally came out with this feature.

So let’s discuss this feature in detail:

This feature provides option for the dual band clients to join the 5 GHz radio compared to the 2.4 GHz range. As we all know that clients on this band (2.4GHz) typically experience interference from Bluetooth devices, microwave ovens, and cordless phones as well as co-channel interference from other APs because of the limit of three non-overlapping channels.

We can use this feature to improve overall network performance. Band direction enables client radios that are capable of dual-band (2.4- and 5-GHz) operation to move to a less congested 5-GHz access point.

Must Remember Points:

***Note: Band Select is configurable only when Radio Policy is set to ‘All‘.

***Note: Band select on supported on all types APs

***Note: This Feature only works when a client first associates to AP.

***Note: This feature will not start when the AP notices a high client count or high channel utilization.

***Note: This feature only goes in one direction (2.4GHz à 5GHz) not the other way (5GHz à 2.4GHz).Means it will not load balance clients on AP.

How it works:

The Cisco accomplishes  this is by delaying/suppressing the first few 802.11b/g probe frames so that client will accept  the 802.11a probes because it will appear to have a quicker response time.

Configuration:

By default it’s disabled.

We can configure this feature globally: Wireless > Advanced > Band Select, and also can be enabled on per WLAN Basis: WLAN > Advanced > Client Band Select. This is useful if we want to disable band selection for a specific WLAN or specific client which is running time sensitive applications (Like:  Voice).

Enable Globally:

Via GUI:

Wireless > Advanced > Band Select

Bandselect1

When configuring the global Band Select features:

  • The cycle count is the number of times a client is denied before being allowed on 2.4 GHz.
  • The cycle period is how much time needs to pass for the next associating attempt to be considered a unique attempt.
  • Age Out Suppression: When the clients will be declared as “new” and may have their probe frames delayed/ignored again.
  • Age Out Dual Band: The AP will not respond to a 2.4 G-Hz probe until a (dual-band) client is no longer marked as dual-band (default is 60 seconds). This is to prevent clients associated on 5 G-Hz radio from switching back to 2.4 G-Hz radio.
  • And the Acceptable Client RSSI is how well a 2.4 GHz client needs to be heard before trying to push them to the 5 GHz band.

Via CLI:

(WLAN1) >config band-select ?
 client-rssi    Sets the client RSSI threshold.
 cycle-count    Sets the Band Select probe cycle count.
 cycle-threshold Sets the time threshold for a new scanning cycle.
 expire         Sets the entry expire.

Enable this feature on per WLAN Basis:

Via GUI:

WLAN > Advanced > Client Band Select

Bandselect2

Via CLI:

(WLAN1) >config wlan  band-select ?
 allow          Allow|Disallow Band Select on a WLAN.
(WLAN1) >config wlan  band-select allow ?
 enable         Allow Band Select on a WLAN.
 disable        Disallow Band Select on a WLAN.
(WLAN1) >config wlan  band-select allow enable  ?
 <WLAN id>      Enter WLAN Identifier between 1 and 16.
(WLAN1) >config wlan  band-select allow enable  8
 WARNING: Allow Band Select on this WLAN may impact time sensitive application like VOICE. Continue? (y/N)y
(WLAN1) >

Verification:

(WLAN1) >show band-select
 Band Select Probe Response....................... per WLAN enabling
 Cycle Count................................... 2 cycles
 Cycle Threshold............................... 200 milliseconds
 Age Out Suppression........................... 20 seconds
 Age Out Dual Band............................. 60 seconds
 Client RSSI................................... -80 dBm
 (WLAN1) >
 (WLAN1) >show wlan 8
 WLAN Identifier.................................. 8
 Profile Name..................................... Test
 Network Name (SSID).............................. Test
 .
 .
 Band Select...................................... Enabled
 Load Balancing................................... Disabled
 Mobility Anchor List
 WLAN ID     IP Address            Status
 -------     ---------------       ------
 (WLAN1) >

That’s all about this feature.

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4 Comments

  1. Hi,I don’t understand the following sentence. This is useful if we want to disable band selection for a specific WLAN or specific client which is running time sensitive applications (Like: Voice).
    What happens when band-select is enabled for client that running time sensitive applications?

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