Error: "Cannot contact the specified host" when reconnecting the host

Products

• VMware vCenter Server

Issue/Introduction

• An ESXi host disconnects from vCenter Server and cannot be reconnected.
• The following error is displayed in the vSphere Client:
  Cannot contact the specified host(<Host-Name>). 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.
• Restarting management agents (services.sh restart) on the host does not resolve the issue.
• Network connectivity tests (e.g., ping, netcat) show intermittent packet loss or timeouts to infrastructure services like DNS.

Environment

8.x

Cause

This issue is caused by physical network instability, packet loss, or configuration errors on the specific uplink (vmnic) currently handling the Management Network traffic. While the link status may appear "Up", the path is not passing traffic reliably.

Resolution

To resolve this issue, validate the health of the physical uplinks and failover management traffic to a healthy redundancy adapter.

1. Log in to the ESXi host via SSH or DCUI and test connectivity to the DNS server or vCenter IP using netcat to verify port reachability:
   nc -z <DNS_IP_Address> 53
nc -z <vCenter_IP> 902
   
   
2. Determine which vmnic is currently active for the Management Network vSwitch.
   esxcfg-vswitch -l
   
   
3. If the host has redundant uplinks, remove the suspected faulty nic (e.g., vmnic4) from the active list or force traffic to the secondary uplink (e.g., vmnic5)
   esxcli network nic down -n vmnic4

 

Once traffic is flowing through the healthy uplink, attempt to reconnect the host in vCenter Server.