This occurred during the process of connecting T310D to ZD1200.
After the AP is linked to the controller, it receives a firmware upgrade and reboots, and the AP state on the controller is disconnect.
And the same symptoms repeat over and over again and again.
What should I check?
ZD1200 ver. 10.4.1.0.226
AP T310D 184.108.40.206.1360
The peculiarity is that it is a closed network that is not connected to the external Internet.
Some factors which may be causing failure.
get syslog log
As your say MTU size was lowered to 1200, but the result was the same.
Symptoms appear as disconnect in the controller status window after the first firmware upgrade, firmware upgrade appears again after reboot and the symptoms continue to be repeated.
The firmware has not been upgraded, and the AP has not been contacted due to continuous reboot.
We tried new equipment and the result was the same.
Before lowering the MTU size, we first need to know if AP-ZD are communicating over a VPN or not. If you are not using VPN, I do not think this as path MTU issue.
I have also provided you the syslog command to see if you can find any error.
If you are unable to figure out, please open a support case.