TCP/UDP sessions limit by user/ip

From:	"Robert Rachuba" <robertr at bskonin dot pl>
To:	<m0n0wall at lists dot m0n0 dot ch>
Subject:	TCP/UDP sessions limit by user/ip
Date:	Tue, 3 Oct 2006 20:37:34 +0200

I would like to limit TCP and UDP sessions by user.
I know that i can just add ipfw rule like that:
ipfw add rule_nr allow tcp from user_IP to any setup limit src-addr number_sessions
But m0n0 "can remember" it to next restart.
How to add that rule permanently?