Remote FortiAP CAPWAP issue

[istvanmarlok]

Hi,

We have a central Fortigate, and we are testing some remote APs. If we are testing it behind a 3rd party 4g modem, CAPWAP tunnel sometimes works but mostly not. It's really unpredictable. We made a capture on the fortigate, I attached a screenshoot about that. 

Has somebody any idea what can cause that?

Thank you!

Best Regards,

Istvan

[adambomb1219]

Any indication of when/why it works and when/why it doesn't?  Any patterns?  Have you tried the remote FortiAP on something other than the 4g modem?  Does the problem only occur when the AP is connected behind this 4g device?   The first thing I would suspect here is an MTU/fragmentation issue.

[istvanmarlok]

Thank you for your answer.

No we didn't find any patterns. Yes If its not behind the 4g device, it works. I guessed MTU too, and I made some tests. I started to ping the Fortigate with 1500 byte packets with df-bit, and it passed.