Connection issue after reboot
 

When I reboot my ESX 4.0, I cant connect to the Vcenter server. Error report appears and says the error code is 503 and cant find server/ server unavailable. What could be the solution?

You have to be sure that DNS is enable from ESX host. That means the DNS has to be reachable and configured.
Another way is that you have to log in as a main root of your ESX host. You have to create a command from the SSH client: tcpdump -nvvvl -i vswif0 port 53
In this way you can see the status of the DNS traffic on the port 53.

Only contact to data center for this type issue.