• vCenter Server cannot connect to the ESX/ESXi host.
• Connecting vCenter Server to the ESX/ESXi host fails.
• vSphere Client cannot connect to the ESX/ESXi host.
• You see one or more of these errors:
  
  
  • Login failed
  • Login failed due to a bad username or password
  • Cannot complete due login due to an incorrect username or password
  • Timed out waiting for server response
  • Failed To Connect to host

1. Verify that you are connecting to the correct hostname or IP address for your vCenter Server. Connections failed because incorrect server information may make the problem seem more complex than it is. Correct any incorrect names, and try connecting to vCenter Server with the vSphere Client. If the connection fails using the hostname but succeeds with IP address then it is probably a DNS error that needs to be corrected.
   
   
2. Verify that network connectivity exists from the Client workstation to the ESX/ESXi host. For more information, see Testing network connectivity with the ping command (1003486).
   
   
3. Verify that the ESX/ESXi Server Management service on the ESX/ESXi host is running. For more information, see Verifying that the Management Service is running on an ESX host (1003494) and Restarting the Management agents on an ESXi or ESX host (1003490).
   
   
4. Verify that you can connect from the vCenter Server to the ESX/ESXi host on port 902 (If the ESX host was upgraded from version 2.x and you cannot connect on port 902, verify that you can connect on port 905). By default ESX/ESXi listens on port 902 and therefore if the previous steps are all correct it most means that a physical firewall is blocking connectivity on port 902. For more information, see Testing port connectivity with Telnet (1003487).
   
   
5. Verify that the you are connecting with the correct username and password. Often, an incorrect username or password has been specified causing the log on failure to occur with the error: Cannot complete login due to an incorrect user name or password.
   
   
6. Verify that the configured permissions for the account are sufficient to allow you to log in to the ESX/ESXi host. For more information, see Troubleshooting permissions errors when connecting to an ESX/ESXi host with the vSphere/Virtual Infrastructure client (1003887).
   

Note: If your problem still exists after trying the steps in this article, please:

• 
  vCenter Server displays the error: Failed to connect to host (1010837)
  
• 
  An ESX/ESXi 3.x or 4.x host takes a long time to boot when the DNS servers are unreachable (1023866)
  
• 
  Cannot connect to the ESX/ESXi host or add it to vCenter Server (1030895)