In my environment I import machines MAC address and machine name into a collection and have the task sequence advertised to that collection. I am not using unknown computer support.
I was trying to PXE boot a client and it kept failing. It would hang on:
Error: PXE-E53: No boot filename received
I initially thought it was a network problem and checked the network configuration on the switches and it was OK. I tested a few other machines and they were able to get an IP from DHCP then contact the PXE service point. So it had to be something linked to this particular client.
On my PXE service point I opened up the SMSPXE.log and searched for the MAC address of the problem client noticed this error:
MAC_ADDRESS: device is not in the database. SMSPXE
MAC_ADDRESS: Not serviced.
I deleted the client and re-imported the client into the collection and it could now PXE boot.
MAC_ADDRESS: device is in the database.
MAC_ADDRESS: using advertisement ZZZZZZZZ