Folks, I am running a dhrelay service and using iptables to be a firewall to block packets from dhcp server on the inbound side, eth0, of my Liunx. The reason to do this is to avoid generating duplicated packets from my machine to dhcp client on the same subnet. For some reasons, I am unable to block these packets. I have a simple rule setting below to simply block all incoming UDP packets where it should block dhcp package as well. iptables -A INPUT -p UDP -i eth0 -j DROP dhcp client are still able to receive duplicated packets, one is from dhcp server and another is from my machine while dhcp relay agent is relaying packets. Any people see this before? Any comments or suggestions are welcome. Thanks, Willy