How to fix HTTP Bad Request (400) error when trying to access FortiManager via FQDN

This article describes how to troubleshoot the issue when there is an HTTP Bad Request (400) error when trying to access FortiManager via FQDN.

Scope

FortiManager.

Solution

For this example, the user is trying to access FortiManager using the following DNS and the web page shows an HTTP Bad Request (400) error. However, there is no issue accessing FortiManager via the IP address associated with the FQDN.

Generally, the HTTP error for Bad Request 400 means there is an invalid HTTP request from the web client. Consider removing any underscores ‘_’ as per the RFC standard whereby some special characters are no longer valid/supported and verify again whether the updated FQDN can be accessed without the Bad Request (400) error code.