Troubleshooting Tip: How to fix 'HTTP 401 Unauthorized', which prevents GUI access and causes issues with SSH

[Ylli_Seitaj]

Description	This article describes how to fix the 'HTTP 401 Unauthorized' error, which prevents GUI access and causes issues with SSH.
Scope	FortiOS v7.2.4.
Solution	Brief network flow:  FortiGate-1 - IPSec tunnel - (management interface) FortiGate-2 Run the following commands to debug any GUI issues:   diagnose debug application httpsd -1 diagnose debug enable After running the above commands, try to access the GUI in order to reproduce the issue. Check the debug logs to see if the following sentence is present: Completed GET request for '/api/v2/monitor/web-ui/extend-session' (HTTP 401 Unauthorized) On both ends of the IPsec tunnel under the Firewall Policies for the IPsec tunnel, change the 'tcp-mss-sender' and 'tcp-mss-receiver' values to 1350 with the following commands: On FortiGate-1 and FortiGate-2: config firewall policy     edit <policy id>        set tcp-mss-sender 1350        set tcp-mss-receiver 1350     next end After executing these commands, the GUI should be accessible and the SSH should work without any issues.