The error shown in the below picture indicates that your host is not reachable by your vCenter server.So first thing you need to do in order to troubleshoot the issue is, try pinging it, if it's pinging and still you can add it, then try pinging it using FQDN name from vCenter... Because if you are trying to add host using FQDN name show in the below picture and your DNS server is down, you can't add host and vCenter throws this error. So i guess it's better add host using IP unless you have best DNS settings on your network.


So be serious while handling ESX / ESXi tasks that involves DNS server.

gil...