Need to duplicate UDP packets to multiple destinations via iptables
You could use the iptables TEE target as long you have the xt_TEE modules in your kernel. You can duplicate packets incoming in your box and send them to another server in your LAN.
Es. to duplicate all incoming dns requests and send them to server 192.168.0.10
iptables -t mangle -A PREROUTING -i eth0 -p udp --dport 53 -j TEE --gateway 192.168.0.10
Another solution is to use a userspace program as http://code.google.com/p/port-mirroring/