If an Access Point loses power (outage, switch upgrade, configured in staging area and powered down to be deployed, etc) the acinfo.conf file that contains the last known Controller IP address is removed on boot up. In this situation, the AP may not be able to get back to it's Primary Controller if the IP address on the AP is on a different subnet than the Controller and:
- There is no static IP address set
- The DNS options for the Controller IP have changed or are not resolvable on the AP subnet
- DHCP options have changed or are incorrect
If the AP is in the same subnet, it will resolve the controller address through SLP.
If the AP reboots, but doesn't power down, it will keep it's acinfo.conf file, and that has the last known AC (access controller) IP.