Recently I came across an issue with Windows DHCP & DNS, specifically related to Cisco AP’s and DDNS. By default Cisco AP’s have period in the hostname (APxxxx.yyyy.zzzz), and this apparently causes issues for Windows DHCP/DNS regarding DDNS. If you have a scope with option 15 (Domain Name) set to foo.bar, and you have clients that only returns option 12 (hostname) and no FQDN (option 81) you’d expect Windows to append option 15 to the hostname. In the case for Cisco AP’s, they seem to only return option 12. You’d then expect Windows DHCP to use APxxxx.yyyy.zzzz.foo.bar as the FQDN for the DDNS update, but this is not the case. In stead, it tries to update the DNS with APxxxx.yyyy.zzzz as the FQDN (where yyyy.zzzz is considered a domain due to the period), hence it will obviously fail, as you don’t have any zone yyyy.zzzz configured in your DNS.