Dual band operation with Band Steering detects clients capable of 5 GHz operation and steers them to that frequency which leaves the more crowded 2.4 GHz band available for legacy clients. This helps improve end user experience by reducing channel utilization, especially in high density environments. Dual band operation with Band Steering is configured on a per-SSID basis. Note that the MR12 and other legacy access points do not support band steering as they only operate on one band.
Wireless devices use two kinds of scanning techniques: passive and active. In a passive scan the wireless client quickly sweeps each channel listening for beacon frames sent by APs advertising their wireless networks. In an active scan the wireless client sends probe requests on each channel to solicit a probe response from APs advertising their wireless network. The end user then sees the list of available wireless network connections. Learn more about 802.11 association.
With Band Steering enabled the AP's beacon frames do not advertise the wireless network. Client devices performing a passive scan will qualify the SSID as hidden.
If the AP hears a probe request from the same wireless client on both 2.4GHz and 5GHz within a short period of time, the AP will only send a probe response advertising the wireless network in response to the 5GHz probe. This steers the client to the 5GHz band (see diagram below). If the AP hears probes from a wireless client on 2.4GHz only, it will respond with a probe request advertising the network.
Figure 1. Band Steering illustrated.
Note: Some wireless devices use passive scanning instead of active scanning because it consumes less power. A single band 2.4GHz wireless client that employs passive scanning may not be able to detect the wireless network with Band Steering enabled because the beacon frames do not advertise the wireless network.
If certain wireless clients are unable to detect the wireless network they may be using passive scanning. In these cases configure the network to use Dual band operation, not Dual band operation with Band Steering.