Controller Based WLANs

What is the parameter for configuring AP load balancing and why is AP load balancing not load balancing clients evenly?

Product and Software: This article applies to ArubaOS 3.1 and later.

 

Load balancing has four major settings:

 

  • Low water mark: Can be set for number of users and network utilization.

  • High water mark: Can be set for number of users and network utilization.

High water mark is the threshold that will enable the load balancing state on the AP. In this state, the AP stops responding to probe requests from a wireless user. Normal drivers will try another BSSIDs (another AP), so we can guarantee that number of users will not exceed high water mark on the AP.

When users begin to leave the AP, it stays in the load balancing state until the number of user falls below low water mark. In this case, the AP leaves the load balancing state and starts responding to probe requests from wireless clients (normal mode).

  • Max Association Retries: The number of probes an AP ignores from the same user to force him to try another BSSID / AP on the same SSID. However, if the user driver is sticky and it keeps probing the same BSSID/AP, the AP responds to him after "Max Retries" of probes. This setting is needed to avoid disconnecting users with old or bad drivers. If this setting is to a very high number, this type of wireless user might get disconnected.

  • Wait time: Time in seconds to wait before enabling or disabling load balancing after the threshold is hit.

 

Note: These parameters are global in 2.5, so they apply to all APs and SSIDs.

 

AP load balancing works by suppressing probe responses from an AP when it hits the configured high water mark. Local-probe-response must be disabled for this to work.

The AP will not respond to client requests based on the configured value of "AP Load Balance Max Retries," which is set to 8 by default. Retries in reference to load balancing include probe requests and authentication requests. If the "Max Retries" limit is reached, an AP stops load balancing. Load balancing is stopped to accommodate persistent clients that tend to connect to the same AP. If AP does not stop load balancing after reaching the maximum number of retries, the chance of client losing wireless connectivity is high.

A better approach is to limit the maximum number of associations on an AP. In this case, local-probe-response can be enabled, which is desirable.

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‎07-01-2014 03:57 PM
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