DNS is critical to proper Virtual Infrastructure operations. Whether its client to server or server to server communications, it is important that all parts involved are using the correct DNS settings and are also registered with the appropriate DNS servers. Unlike Windows, ESX servers will not auto-register their IP addresses with the DNS servers. (Windows machines will typically update the DNS servers in an Active Directory when you join them to the domain – Since ESX servers are not Windows servers, they are never joined to the domain). You will have to manually add the ESX hosts to your DNS servers for proper resolution. Without it, expect weird vMotion, DRS and HA issues. Even simple things like adding the host to VirtualCenter or connecting to a virtual machine console will be problematic with screwy DNS.
Updating your DNS servers is also another good way to make sure that the IP address is not already in use. Many smaller shops (and some bigger ones too) do not have proper IP address management programs so DNS might be their last line of defense. Be aware that some ESX hosts might have multiple IP addresses that don’t always ping back. Adding these supporting IP addresses (vMotion, iSCSI) into DNS will at least show an administrator that they should double-check before using them. I’ve been to countless clients where pinging an IP was the method to determine IP availability. :)
Finally, Aaron Silber sent me over a nice GUI alternative to NSLookup when dealing with DNS and IP address resolution.
Check out the free download from NirSoft here.