ESXi host will not reconnect to vCenter after an upgrade from 6.7 to 7.0.3 to 8.0.3 and fails at 80%

Products

• VMware vSphere ESXi

Issue/Introduction

• A recent upgrade may have taken place from 6.7 to 7.0.3 to 8.0.3.
• A host that was previously connected to the vCenter prior to the upgrades may fail to connect at 80% with the following error message in the Task Console:
  
  Cannot contact the specified host (esxi.example.com). The host may not be available on the network, a network configuration problem may exist, or the management services on this host may not be responding.

Environment

vCenter 8.0.3
ESXi 8.0.3

Cause

This can be caused by host vSwitch misconfiguration or due to port 902 being blocked on the firewall.

Resolution

1. Check and validate the vswitch and uplink configuration of the host that is mapped for management network.

         esxcfg-vswitch -l

         esxcfg-nic -l

   Add or remove the missing uplinks(if any) using below command
         esxcli network vswitch standard uplink [add|remove] --uplink-name=vmnic# --vswitch-name=vSwitch

2. Test port 902 with nc from vCenter, a successful connection will look like:

root@vchostname [ ~ ]# nc esxi.example.com 902
220 VMware Authentication Daemon Version 1.10: SSL Required, ServerDaemonProtocol:SOAP, MKSDisplayProtocol:VNC , VMXARGS supported, NFCSSL supported/t, SHA256 supported

You will need to break out of the nc with Ctrl+C.

If text similar to this does not display, then port 902 is blocked and it is recommended to check the environment for firewalls that may be blocking the traffic.

Additional Information

https://ports.broadcom.com/ can be used to determine which ports are required for proper network communication between vcenter and the hosts.
Troubleshooting an ESXi host in a "not responding"/"disconnected" state (KB 344682) can be used as a general guide for host connectivity issues.