scripts & cron

I have setup successfully an openVPN network across the continent using DD-wrt.

Now I want to use the Asusmerlin openVPN to act as a server.

I've found in DD-WRT clients on other networks sometimes pick DHCP from other openVPN subnets.

To avoid this, and everyone stay in their own network (gateway/dns/etc) but everyone can connect to every single client in other subnets (openVPN clients) I've setup a class B network and use a script on DD-wrt to avoid wrong DHCP servers from other subnets.

I've put the following script in the "Cron" tab of the DD-wrt router:

@reboot sleep 30;/sbin/insmod /lib/modules/2.6.24.111/ebtables.o;/sbin/insmod /lib/modules/2.6.24.111/ebt_ip.o;/sbin/insmod /lib/modules/2.6.24.111/ebtable_filter.o;ebtables -F;ebtables -I FORWARD -i tap0 -p IPv4 --ip-protocol udp --ip-destination-port 67:68 -j DROP;ebtables -I FORWARD -o tap0 -p IPv4 --ip-protocol udp --ip-destination-port 67:68 -j DROP;ebtables -I INPUT -i tap0 -p IPv4 --ip-protocol udp --ip-destination-port 67:68 -j DROP;ebtables -I OUTPUT -o tap0 -p IPv4 --ip-protocol udp --ip-destination-port 67:68 -j DROP

How would I do this in Merlin-Asuswrt or is this not necessary on Merlin-Asuswrt for a class B network spanning the continent?