Enabling aggressive load balancing on the controller allows lightweight access points to load balance wireless clients across access points. You can enable aggressive load balancing using the controller.
When a wireless client attempts to associate to a lightweight access point, association response packets are sent to the client with an 802.11 response packet including status code 17. The code 17 indicates that the AP is busy. The AP responds with an association response bearing 'success' if the AP threshold is not met, and with code 17 (AP busy) if the AP utilization threshold is reached or exceeded and another less busy AP heard the client request.
For example, if the number of clients on AP1 is more than the number of clients on AP2 plus the load-balancing window, then AP1 is considered to be busier than AP2. When a client attempts to associate to AP1, it receives an 802.11 response packet with status code 17, indicating that the access point is busy, and the client attempts to associate to a different access point.
You can configure the controller to deny client associations up to 10 times (if a client attempted to associate 11 times, it would be allowed to associate on the 11th try). You can also enable or disable load balancing on a particular WLAN, which is useful if you want to disable load balancing for a select group of clients (such as time-sensitive voice clients).
Clients are load balanced between access points on the same controller. Load balancing does not occur between access points on different controllers.
The maximum number of client associations that the access points can support is dependent upon the following factors:
- The maximum number of client associations differs for lightweight and autonomous Cisco IOS access points.
- There may be a limit per radio and an overall limit per AP.
- AP hardware (the 16-MB APs have a lower limit than the 32-MB and higher APs)
The Client Association Limits for Lightweight Access Points are as follows:
- For 16-MB APs, the limit is 128 clients per AP. This limit is applicable to 1100 and 1200 series APs.
- For 32-MB and higher APs, there is no per-AP limit.
The maximum Client Association Limits per-radio for all the Cisco IOS APs is 200 associations.
With 32-MB and higher lightweight Cisco IOS APs, with two radios, up to 200 + 200 = 400 associations are supported.
The maximum Client Association Limits per Autonomous Cisco IOS access point is around 80 to 127 clients per AP. This number varies depending on the following factors:
- AP model (whether it is 16 MB or 32 MB or higher)
- Cisco IOS software release
- Hardware configuration (two radios use more memory than one)
- Enabled features (WDS functionality in particular)
The per-radio limit is about 200 associations. One association will likely hit the per-AP limit first. Unlike Cisco Unified Wireless Network, autonomous Cisco IOS supports per-SSID/per-AP association limits. This limit is configured using the max-associations CLI, under dot11 SSID. The maximum number is 255 associations (which is also the default number).