Error: "Unknown Reason" when trying to log in to ESXi Host Client

Products

• VMware vSphere ESXi

Issue/Introduction

• Error "Unknown Reason" Your browser sent a request that this server could not understand. Additionally, a 400 Bad Request error was encountered while trying to use and ErrorDocument to handle the request.
• 
• ESXi host showing as disconnected from the vCenter 

Environment

VMware vCenter Server 8.0.X

VMware vCenter Server 7.0.X

VMware vSphere ESXi 8.0.X

VMware vSphere ESXi 7.0.X

Cause

• Ports between the vCenter and ESXi host are closed

Resolution

1. Engage with your Network Team to open ports between the vCenter and ESXi host on the firewall 
2. Read more at Troubleshooting ESXi Host in Disconnected State and Unable to Connect to vCenter