I was lucky enough to grab a copy of the vSphere 5 suite this weekend. Upgrade went fine, but I encountered an error during the install process for vCenter 5 stating “The Fully Qualified Domain Name could not be resolved”, after doing some testing I had no issue resolving that to my IP address assigned to the server, I was a bit confused at it but I clicked OK though it and the install worked fine. Later that day I decided to migrate one of my VM’s over to another datastore, but I encountered an error stating “Could not connect to host”, this also seemed to have affected deploying templates too. After much troubleshooting and digging, I found @2vcp‘s post, which at the very end stated I would need a PTR record, after adding this everything worked like a charm. What working at a hosting company has taught me is that 90% of the issues are either permissions or DNS related.

UPDATE:

I previously didn’t have a host within my own network, only the vCenter server. Upon having this issue happen again “Cannot connect to host” when deploying templates or migrating data, I found out that this was caused by TCP port 902 not being opened on my firewall. As previously posted, I have another machine outside of my network, so in order for that to work, I have to set my managed IP to my ISP provided IP. The hosts inside the network also rely on this and not the internal IP, once I made a rule to forward that port to my ESXi host, everything worked as normally. I’m sure I thought I fixed the issue, because the first time I tried fixing the FQDN issue, I had uninstalled/reinstalled vCenter and removed the vCenter agent, I can only think that the vpxa.cfg was never updated with the managed IP address.