How can I limit some port according to ethernet card MAC?

[heath, Chia Hui Chen]

Hello,
I use FreeBSD 5.2.1 as NAT.
How can I limit some port (packet in and out) according to ethernet card MAC
?
Because we use dhcpd, and the IP is dynamic, so I wanna limit it by MAC.
What can I do? Thanks for your response!

Best Regards,
- heath