filtering by mac address

Hello: Is it possible to setup pxe to filter requests via mac
address?? I am trying to setup a group of linux terminals using
LTSP.org software. The problem is that pxe will talk to any
workstation set for network booting. I need pxe to basically ignore a
subset of workstations based on their mac address. Is this possible??
Or is this really a dhcp issue?? I don't know.

All help greatly appreciated, Chris.

System Info: OES sp1 (NW kernel), ZfD 7.0.

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