DNS Gotchas in vSphere

As I once again immerse myself in a VMware environment as System Administrator, I am getting to do all sorts of fun stuff that I haven’t done in a while.  However there is one gotcha that I encountered that I know, I knew, and have even taught on countless occasions.

VMware does not do Dynamic DNS.  That is, it does not automatically create a DNS entry for your hostnames (and other fun stuff like VMkernel and HA Management).. which is fine, as long as you have an eidetic memory and never assign those IP addresses to anything else… and you are the only person who will ever configure anything on your network.

If those are not the case, you have to document them… and you need to manually create addresses in DNS.  Since most of us probably use Microsoft DNS for internal use, all we have to do is pop open the DNS Management console and create the appropriate A Records.

What happens if I don’t?

Simple… nothing, now.  As you are looking at your systems and it is fresh in your mind you won’t have any problems.  However later on, when you have long forgotten that you configured a new host, or applied a host profile to a new server, things will go wrong, and you won’t know why.  Did I mention, by the way, that VMK and HA Management ports don’t reply to Ping, so once you have double-assigned the same IP address to something else, troubleshooting will not be enjoyable.

A lot of ports such as these are not actually used by DNS ever, so left alone they wouldn’t be an issue… until you assign the address to another device.  creating a dummy record in DNS will save you the headaches later on.

Another benefit of doing this, by the way, is that although the same ports will still not respond to a Ping, a Ping -a <address> will return a hostname!

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