All modern IDRAC versions limit access to the web interface to a limited list of addresses. Accessing the IDRAC over the public IP and network NAT is a problem in this case. Usually, you get the error Access Error: 400 – Bad request. Especially when using a Reserse Proxy such as Nginx Proxy Manager.

To disable run the following via racadm or enable the SSH service on IDRAC and SSH and run.

racadm set idrac.webserver.HostHeaderCheck 0