How to restrict pppoe users on nas-port-id

[eugene at snowball.co.za]

 I'm using FreeRADIUS Version 1.0.4 with Dialup_admin and mysql and I
would like to know if anyone can direct me in the right place to find
out how to restrict pppoe users from logging in from multiple NAS port
IDs. I would like to restrict them to logging on to only a specific set
of port IDs that comes from a database. Any help will be appreciated.

-Eugenevdm