APs randomly disassociate from WLC ver 4.1.185.0

Question

I have a WLC 4402 with about 45 1010 APs installetion
WLC code version 4.1.185.0 and APs randomly disassociate from WLC - it happens usually one-two times a day
with an errors:
AP's Interface:1(802.11b) Operation State Up: Base Radio MAC:00:0b:85:xx:xx:xx Cause=Unknown
AP's Interface:1(802.11b) Operation State Down: Base Radio MAC:00:0b:85:xx:xx:xx Cause=Max Retrasmission
I've tried the suggested solutions putting a static ARP entry and moving AP's to different VLAN but nothing works unless the AP's physically rebooted.
I think the problem begin just after upgrading to 4.0.217.0
please note when AP's disassociates from WLC its still reachable via ping
Are there any specific requirements for newer versions?
Please advice

Answer 1

Layer 2 mode uses a different non-routable method of AP to WLC connection. By moving to layer 3 you enabled IP on the access points. This is why you were able to reassociate. Layer 2 should only be used when all the APs and the controller are on the same network segment. Bear in mind, Layer 3 is your friend. It will allow latency based applications to work much better and more reliable. Layer 2 is really only used to prepare the APs for some specific configurations that require a quick, clean connection to a controller.