Event ID 1340 warnings are consistently being logged on a Server 2012 R2 domain controller in the System log whenever Apple/Mac clients connect to the network. Here's a log example:
Log Name: System
Source: Microsoft-Windows-DHCP-Server
Date: 8/10/2015 5:00:33 AM
Event ID: 1340
Task Category: None
Level: Warning
Keywords: Classic
User: N/A
Computer: myserver.mydomain.com
Log Description:
The DNS registration for DHCPv4 Client IP address 192.168.1.51 , FQDN
hostname.mydomain.com and DHCID AAEBVzZyBqmkeAK+NSOo3wSKL= has been
denied as there is probably an existing client with same FQDN
already registered with DNS.
I'm aware this is related to the fact that I have DHCP Name Protection enabled, but the feature works fine for all Windows & Android devices. The logs seem to be present for all Mac and iOS devices. It doesn't appear to impact the client's connectivity however.
I've confirmed that DHCIDs (which are used by the non-Windows clients in DHCP name protection) populate in DNS correctly – even for the Apple clients. Also, the DNS zone is AD integrated with secure dynamic updates enabled. Note that when I first enabled name protection I saw these all the time, until I went through steps to configure the DHCP server to own all records it registers. I've also confirmed that no additional adapters are attempting network connections (wifi is disabled when cabled connections are used, for example.)
So, the last piece of this puzzle is: why is this still happening on the Apple DHCP clients? I'm not satisfied with administrative events populating for "routine" items like these if I can resolve it with diligent configuration.
Best Answer
Looks like all the Mac machines have the same default hostname. Set reservations with hostnames for each different machine or set the hostname on the Apple MAC itself.