ESXi host down

ESXi

1. Verify that the ESXi host is in a powered ON state. For more information, see Determining why an ESXi/ESX host was powered off or restarted (1019238).
2. Verify that the ESXi host can be reconnected, or if reconnecting the ESXi host resolves the issue. For more information, see Changing an ESXi or ESX host's connection status in vCenter Server (1003480).
3. Verify that the ESXi host is able to respond back to vCenter Server at the correct IP address. If vCenter Server does not receive heartbeats from the ESXi host, it goes into a not responding state. To verify if the correct Managed IP Address is set, see Verifying the vCenter Server Managed IP Address (1008030) and ESXi 5.0 hosts are marked as Not Responding 60 seconds after being added to vCenter Server (2020100). See also, ESXi/ESX host disconnects from vCenter Server after adding or connecting it to the inventory (2040630) and ESX/ESXi host keeps disconnecting and reconnecting when heartbeats are not received by vCenter Server (1005757).
4. Verify that network connectivity exists from vCenter Server to the ESXi host with the IP and FQDN. For more information, see Testing network connectivity with the ping command (1003486).
5. Verify that you can connect from vCenter Server to the ESXi host on TCP/UDP port 902. If the host was upgraded from version 2.x and you cannot connect on port 902, then verify that you can connect on port 905. For more information, see Testing port connectivity with Telnet (1003487).
6. Verify if restarting the ESXi Management Agents resolves the issue. For more information, see Restarting the Management agents on an ESXi or ESX host (1003490).
7. Verify if the hostd process has stopped responding on the affected ESXi host. For more information, see Troubleshooting vmware-hostd service if it fails or stops responding on an ESX/ESXi host (1002849)
8. The vpxa agent has stopped responding on the affected ESXi host. For more information, see Troubleshooting the vCenter Server Agent when it does not start (1006128)
9. Verify if the ESXi host has experienced a Purple Diagnostic Screen. For more information, see Interpreting an ESX/ESXi host purple diagnostic screen (1004250)
10. ESXi hosts can disconnect from vCenter Server due to underlying storage issues. For more information, see Identifying Fibre Channel, iSCSI, and NFS storage issues on ESXi/ESX hosts (1003659