Troubleshooting ESXi Host in Disconnected State and Unable to Connect to vCenter

Products

• VMware vCenter Server 8.0

Issue/Introduction

• An ESXi host appears in a Disconnected state in vCenter Server and cannot be reconnected.
• When attempting to reconnect the host to vCenter, the operation fails with the following error message: Unable to communicate with the remote host, since it is disconnected.

Environment

VMware vCenter Server 8.x

VMware vCenter Server 7.x

VMware vSphere ESXi 8.x

VMware vSphere ESXi 7.x

Cause

• This issue occurs when the ESXi host name is mapped to multiple IP addresses in DNS (duplicate or incorrect DNS records).
• vCenter Server attempts to communicate with the ESXi host using an IP address that does not match the active management network configuration of the host, causing connectivity failures.

Resolution

Follow the steps below to resolve the issue:

• 1. Verify Network Connectivity on Port 902 and 443

  • Run the following commands from a vCenter Server SSH session:

    curl -v telnet://<HostIPAddress>:443

    curl -v telnet://<HostIPAddress>:902

  • Run the following commands from an ESXi host SSH session:

    nc -zuv <vCenterServerFQDN> 902

    nc -zv <vCenterServerFQDN> 443

Confirm that the port is open and reachable.

• 2. Verify DNS Resolution for the ESXi Host
  • Run an nslookup for the ESXi host name: nslookup <ESXi_FQDN>
  • If the command returns multiple IP addresses, this indicates a DNS misconfiguration.
• 3. Correct Duplicate DNS Records
  • Identify the correct management IP address assigned to the ESXi host.
  • Remove any duplicate or incorrect IP address entries for the ESXi host from DNS.
  • Ensure the ESXi host name resolves to only one valid management IP.
• 4. Validate ESXi Management Network Configuration
  • Log in to the ESXi host directly using the ESXi Host Client.
  • Navigate to Networking > VMkernel adapters.
  • Verify which IP address is assigned to the Management Network.
  • Confirm that this IP matches the corrected DNS record.
• 5. Reconnect the ESXi Host to vCenter
  • Once DNS records are corrected and network connectivity is verified:Return to vCenter Server.
  • Attempt to reconnect the ESXi host.

The host should now successfully reconnect and appear in a Connected state.