firewall with OpenBSD

[Negrea Mihai <mihai_(_at_)_umft_(_dot_)_ro>]

Hi all,

 I want to build a firewall for my school's network. Could anyone give me
any links on how to implement the following features:
-packet filtering with ipfilter - advanced
-intrusion detection system
-NAT
- maybe dynamic routing

I want to do it with Open BSD of course.

Thanks in advance!

Mike