Strange indeed.
I guess I have a 'basic setup' with 3 interfaces, WAN, LAN and OPT1, my Portal interface with its own DHCP instance.
When I activated "Deny Unknown clients" my logs started to fill up with:
06-21-2014 17:50:02 Local7.Error 192.168.1.1 Jun 21 17:50:06 dhcpd: DHCPDISCOVER from 0c:77:1a:2b:13:35 via sis0: network 192.168.2.0/24: no free leases
06-21-2014 17:49:54 Local7.Error 192.168.1.1 Jun 21 17:49:58 dhcpd: DHCPDISCOVER from 0c:77:1a:2b:13:35 via sis0: network 192.168.2.0/24: no free leases
06-21-2014 17:49:49 Local7.Error 192.168.1.1 Jun 21 17:49:53 dhcpd: DHCPDISCOVER from 0c:77:1a:2b:13:35 via sis0: network 192.168.2.0/24: no free leases
06-21-2014 17:49:47 Local7.Error 192.168.1.1 Jun 21 17:49:51 dhcpd: DHCPDISCOVER from 0c:77:1a:2b:13:35 via sis0: network 192.168.2.0/24: no free leases
And of course, my 'client' device didn't get an IP anymore …...
The only thing I don't have neither use, is VLANs ......