I have an application where I need to configure a router to pass through ping requests (ICMP type 
through to the LAN port. I have a Linksys WRT54GS with tiny DD-WRT V24 SP2 installed. I am adding the following iptables rules:
iptables -t nat -I PREROUTING -p icmp --icmp-type 8 -s 72.64.140.50 -j DNAT --to-destination 192.168.1.200
iptables -t filter -I FORWARD -p icmp --icmp-type 8 -s 72.64.140.50 -d 192.168.1.200 -j ACCEPT
iptables -t nat -I POSTROUTING -p icmp --icmp-type 8 -s 72.64.140.50 -d 192.168.1.200 -j ACCEPT
The intent is that the first rule will change an incoming echo request destination to the unit on the LAN which I want to receive the ping request.
The second rule allows the modified echo request to pass through the FORWARD table.
And the last one allows the modified echo request to pass through the POSTROUTING table.
When I send a ping to the router with four tries, I get no pings out the LAN. Using iptables -L -v -n I can see were rule #1 passes one packet (but not four), rule #2 passes four packets (good!) and rule #3 passes 1 packet.
At this point I am at loss as to why this is not working. Can someone help me out here?