Product and Software: This article applies to all Aruba controllers and ArubaOS versions before 5.0.
The master IP address in an AP system profile must be set only to the IP address of the master controller. Different APs in the same master-local deployment cannot be set to different controller IP addresses. This will break WIDS.
All APs and AMs talk to the master controller, which is where all the monitored AP and client info and WIDS events are saved.
APs talk to the master directly, and therefore they need connectivity to the master controller for classification and WIDS to work correctly. By default APs will use the master IP setting on the local controller. Sometimes this address is not routable from the APs. The 'master-ip' setting is a way to configure a routable address for the master controller, so that the APs can still reach the master.
For ArubaOS 3.x, the AP talks to the master directly.
Starting with ArubaOS 5.0, APs communicate with the master through the local. That is where the 'master-ip' command has been deprecated.