Exclude ONE IP from internet access?

[Bamsefar]

Well I have white rules in my ASUS router, however I need to exclude internet access for ONE client all the time. Since I run white lists I can not use black list at the same time (as far as I know anyway). Is there any way, iptables command or something, I achive this without turning my system inside and out (that is rearrange DHCP and static IPs and so on - a major operation if you ask me)? A simple iptables command maybe

 

[sinshiva]

/jffs/scripts/firewall-start

#!/bin/sh
iptables -A FORWARD -o `nvram get wan0_ifname` -m mac --mac-source 01:23:45:67:89:AB -j DROP

chmod a+rx /jffs/scripts/*