ESXi refuses AD join, "The host does not have a suitable FQDN"

Solution 1:

Read the relevant documentation for your product.

http://pubs.vmware.com/vsphere-60/index.jsp?topic=%2Fcom.vmware.vsphere.networking.doc%2FGUID-6BC115DF-4EC5-409E-8B74-45525E966F0F.html

The documentation clearly states that ipv6 is not supported for ESXi -> Active Directory communication. (as of 6.0.)

Solution 2:

Honestly, if this is a standalone host, it's not worth joining it to a domain. Ideally you join your vCenter Server to Active Directory, not the individual hosts.