Environment : This article applies to all Aruba Instant platforms and versions.
When the first AP comes up, it elects itself as the master because no one is available to preempt it. The following message is displayed on the console of the AP.
This AP listens for the Discovery Protocol on the wired side. When a new AP comes, it sends out a Discovery Protocol. AP1 (master) responds to it and the new AP accepts AP1 as the master and gets the configuration from it via PAPI (UDP 8211).
The process continues for new APs that join the network until the cluster size reaches 16 (maximum limit). At this point, the cluster topology is complete and no change occurs until the master (AP1) fails.
If a new AP (the 17th AP) is plugged into the network, it is not able to join the discovery process because the cluster has reached its maximum limit. Also, the 17th AP cannot start a new cluster because it is part of the same broadcast domain as the original cluster.
When the master AP goes down, the AP that is second-in-line (the AP that came up after the master) advertises and becomes the master.