There are two feature enhancements to load balance clients on the Cisco Wireless LAN Controllers in software release 6.x and higher. Although there are similarities, both features work independently of each other and can be enabled or disabled independently. These are:rn1. Aggressive Load Balancing - Enhancement from previous version.rn2. Band Select or Band Direction - New feature that encourages dual band clients to connect to 5 G-Hz networks.
The previous version of aggressive load balancing was sometimes not reliable as it relied on the client NICs? implementation to balance client connections across multiple access points. The feature used a reason code 17 as a part of the association response to a client to indicate that an AP is unable to handle any more STAs and that the STA should try another AP. While the 802.11 specification does define what the reason code 17 is, it does not define how a STA must respond to one ? as long as they process it. The previous version of load balancing only denied a client once at maximum and eventually allowed the client to associate on the second attempt. Moreover, the configuration was globally defined per controller (Controller > General) and there was no way to disable it (selectively) for time sensitive voice clients. CLI options on the legacy ABL feature
config load-balancing enable
config load-balancing window
The enhancement to Aggressive Load Balancing (in 6.x and 7.x software) allows you to configure load balancing per WLAN. The feature is disabled by default. The configurable options are defined globally (Wireless > Advanced > Load Balancing), but the feature itself can be enabled per WLAN (WLAN > Advanced > Client Load Balancing).
Use the following CLI command to configure load balancing for a specific WLAN:
config wlan load-balance allow wlan
The global configuration options are:-
(WLC) >config load-balancing ?
window Configures Aggressive Load Balancing client window.
denial Configures Aggressive Load Balancing denial count.
(WLC) >config load-balancing window ?
Number of clients (0 to 20)
In dense production networks, the controllers have been verified to function optimally with load-balancing ON and window size set at 10. In practical terms, this means load-balancing behavior is only enabled when, for example, a large group of people congregate in a conference room or open area (meeting or class). Load-balancing is very useful to spread these users between various available APs in such scenarios.
(WLC) >config load-balancing denial ?
Number of denials <1-10>
Note: Users are never "thrown off" the wireless network. Load-balancing only occurs upon association and the system will try to encourage a client towards a more lightly loaded AP. If the client is persistent, it will be allowed to join (after passing the number of denials count) and will never be left stranded.
It's recommended not to enable this feature for the voice WLAN as it can cause roaming issues. For other WLANs, it should be enabled only after testing.
The 2.4-GHz band is often congested. Clients on this band typically experience interference from Bluetooth devices, microwave ovens, and cordless phones as well as co-channel interference from other access points because of the 802.11b/g limit of three non-overlapping channels. You can use this feature to combat these sources of interference and 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.
Band selection works by regulating/suppressing probe responses from the clients? 2.4 GHz radio. It makes 5-GHz channels more attractive to clients by delaying probe responses on the 2.4-GHz channels. The feature is disabled by default. The configurable options are defined globally (Wireless > Advanced > Band Select), but the feature itself can be enabled per WLAN (WLAN > Advanced > Client Band Select). This is useful if you want to disable band selection for a select group of clients (such as time-sensitive voice clients).
Use the following CLI to enable this feature on the WLAN:
(WLC) >config wlan band-select allow enable
The global configuration options are:
(WLC) >config band-select ?
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.
client-rssi Sets the client RSSI threshold.
Although this feature is designed to help 802.11n capable dual band clients to select the 5Ghz band (and utilize the bonded/40MHz wide channels on the 5Ghz frequencies), it has to be used with caution on voice enabled WLANs (with time-sensitive voice clients) as it can cause roaming delays or dropped calls. Please make sure you test it thoroughly in your environment with the dual band clients before enabling it.
Please note some of the limitations of these enhancements:-
Adding information shared by George Stefanick:-
Kevin -- This is because not all clients will honour code 17 from the access point telling the client that the ap is busy. While some client do.
It is the responsibility of the client to honour, process or discard that association response frame with reason code 17. Some clients ignore it, even though it is part of the 802.11 specification. The standard dictates that the client driver must look for another AP to connect to since it receives a "busy" message from the first AP it tries. Many clients do not do this and send the association request again. The client in question is allowed on to the wireless network upon subsequent attempts to associate.
Q. The client load balancing feature for a Cisco WLC. Basically, if Client Load Balancing is enabled on a WLAN, will clients in that particular WLAN be balanced based on the total client count on the AP or the client count on that AP in the specified WLAN?
A. Using Aggressive load balancing the LAP can be configured to load balance clients among AP on a per WLAN basis.