50G 7.4.9 - MTU Issues?

[rewater]

I plugged my new 50G in before going away for a week. Everything seemed fine in the 24 hours prior to me leaving. When I got back, it seems there are issues, and I notice about 12 hours ago, I was upgraded to 7.4.9 from 7.4.8. It's like there is an MTU mismatch, but I have my WAN set to DHCP and it's auto selected 1500, so I think that looks fine.

Are there any other issues that might cause packet loss or intermittent internet issues, esp on wireless devices (connected to the Fortigate by TPLINK AP's).

Sorry, it's a bit vague, this is definitely new behaviour since either the switch to the 50G from my 60F (brand new install) or since the deployment of 7.4.9 by Fortinet.

TIA for any ideas.

[Jean-Philippe_P]

Hello rewater, 

Thank you for using the Community Forum. I will seek to get you an answer or help. We will reply to this thread with an update as soon as possible. 

Thanks, 

[Jean-Philippe_P]

Hello,

We are still looking for an answer to your question.

We will come back to you ASAP.

Thanks,

[Jean-Philippe_P]

Hello rewater,

I found this solution. Can you tell us if it helps, please?

To troubleshoot the packet loss or intermittent internet issues you're experiencing, consider the following steps:

1. Check Interface Speed and Duplex Settings:

   • Ensure that the speed and duplex settings on the FortiGate interfaces are correctly configured. Use the CLI command dia hard device nic <interface name> to verify settings.
   • If there are errors, manually set the speed using:

     config system interface
     edit <interface name>
     set speed 100full
     end
     

2. Review Bandwidth Usage: High bandwidth usage can cause packet loss. Enable logging on firewall policies to generate bandwidth reports. Go to Firewall -> Policy and enable 'log allowed traffic'.
   
   

3. Check for Known Issues: Review the release notes for v7.4.9 for any known issues that might affect your setup. Ensure that the upgrade did not introduce any new bugs.
   
   

4. Verify MTU Settings: Although you mentioned the MTU is set to 1500, ensure that all devices in the network path, including the TP-Link APs, are configured with compatible MTU settings.
   
   

5. Examine Wireless Configuration: Check the configuration of your TP-Link APs to ensure they are not causing the issue. Look for any firmware updates or settings that might need adjustment.
   
   

6. Network Changes: Consider any recent changes in the network setup, such as new equipment or configuration changes, that might have coincided with the issue.
   
   

7. Run Diagnostics: Use diagnostic tools on the FortiGate to capture and analyze traffic. Commands like diagnose sniffer packet can help identify where packets are being lost.

By following these steps, you should be able to identify and resolve the cause of the packet loss or intermittent issues. If the problem persists, consider reaching out to Fortinet support for further assistance.

[BillH_FTNT]

Hi @rewater 

what is your issue ? Could you please share more details ? 

Bill

[distillednetwork]

I have seen some ISPs have issues where even though the MTU was negotiated, there was an issue downstream causing packet loss.  You can test by adjusting the TCP MSS values to something lower on a test firewall policy to see if that fixes your issue:

https://community.fortinet.com/t5/FortiGate/Technical-Tip-Setting-TCP-MSS-value/ta-p/194518