Monday, November 29, 2010

CAPWAP Controller Selection Process

Once a CAPWAP access point has discovered and built a list of all one or more available wireless LAN controllers, it is ready to select the optimal controller to join.

Controller selection is based on the following information embedded in the Discovery Response from each candidate controller:
1.      Controller sysName
2.      Controller Type
3.      AP Capacity
4.      Current AP Load
5.      Master Controller Status
6.      AP-Manager IP Address(es)
7.      Current AP Load on each AP-Manager IP Address

The AP will select a controller based on the following precedence rules:
1.      Primary configured controller preference
2.      Secondary configured controller preference
3.      Tertiary configured controller preference
4.      Primary Backup controller (WLC version 5.0 and later)
5.      Secondary Backup controller (WLC version 5.0 and later)
6.      Master Controller status of WLC
7.      Controller with greatest excess capacity
a.       Ratio of current AP load versus maximum capacity; expressed as a percentage

Note – Once an access point joins a controller, it learns the information of all controllers within the Mobility Group and stores their IP addresses in NVRAM. The AP may join another controller with greater excess capacity if no controller preferences are configured.


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