FortiGate 60F PPPoE weird behavior with some services

[prigekhas]

Hi all. Hoping this community can shed some light. I have CenturyLink fiber 1GB to my home, and have been using a UBNT Edge router to connect to this and have had zero issues.

I was recently given a FortiGate 60F running v7.4.2 to demo and wanted to use this as my primary edge device at home. I am pretty familiar with FortiGates and manage about 26 of them, however none using PPPoE for connectivity https://tutuapp.uno/ .

I set the FortiGate using WAN1 to connect to CenturyLink via PPPoE and all has been working, Apple TVs, iPhones, Androids, Tesla, etc was all connected and no issues. However some services just wouldn’t work, all my Roku TVs stopped, however I could see traffic passing as expected, but it just wouldn’t play anything. My Rivian would connect to WiFi and pass data no worries, but in the Rivian app it would show the vehicle was offline and not connected to the cloud.

I moved the CenturyLink connection back to the UBNT router and setup the WAN interface on the FortiGate with a local address but kept everything connected to the FortiGate, everything started working again.

Is there something I’m missing on the FortiGate PPPoE setup that might be causing a small handful of services not to work?

Hope this all makes sense.

[AEK]

Hello

First question to ask is what is different between Ethernet and PPPoE that may have caused the issue? At first I just think about MTU. You may check this side.

[hbac]

Hi @prigekhas,

You can try to lower tcp-mss values under the outbound firewall policies. Please refer to https://community.fortinet.com/t5/FortiGate/Technical-Tip-Setting-TCP-MSS-value/ta-p/194518

Regards,