I feel I need to add this, so people stumbling across the post understand.
The UNIQUE key for the hostMAC table is one key with two columns (hmMAC, hmHostID). Basically this means, a MAC cannot exist multiple times for the SAME host, but they can appear multiple times for different hosts. The idea is to allow the mac’s to show up with the hosts they reside in, but when it comes to identifying a host based on the MAC address, this becomes much more of a “no man’s land”.
This, we hope, will not be the case for much longer. One, MAC Addresses can be spoofed (and the same mac can exist on different machines even) so we’ve kind of lost the MAC Address as a unique identifier for a host. It probably doesn’t help that it’s not uncommon for a Laptop to have 2 or 3 MAC Addresses on it. Image an organization with only 1000 laptops. That’s potentially 2000 to 3000 MAC Addresses. Now I realize the unique identifier number is extremely high (each manufacturer has a potential of 16,777,215 addresses available) but as you see you can have the same mac address on multiple systems, it’s not very good for the hometeam.
It is uncommon to see the error itself, but when it has come up it’s usually because of a VM or TUNNEL adapter that is embedded as a part of the image. This, more or less, is where the pending filter comes in though.
While this field was, I think, only intended to filter any incoming “pending” mac addresses, it really should be applied to any mac address and it has been made to do exactly that.