I recently noticed that some of my client machines (Windows 7 Enterprise x64) get Netlogon Event 5719 on every startup. This points to a DHCP issue, according to this KB article:
http://support.microsoft.com/kb/2459530
I'm using PFSense as a router between the client's vlan and dhcp server's vlan and as DHCP relay agent. I'm still on version 2.1.3
As far as I understood the issue there are 2 types of DHCP responses possible to be sent back to the client: broadcast or unicast mode. Which mode to be used by the relay agent should be determinded by a flag set in the request that is sent by the client.
Apparently the problem is that PFSense does not support both modes and a timeout occurs on the requests that ask for a unicast response....