my configuration in iptable is follows:
iptables -t nat -A PREROUTING -d externalip -p tcp -m tcp -dport 80 -j DNAT --to-destination internalip:80
iptables -t nat -A POSTROUTING -s internalip -o eth1 -j MASQUERADE
both the commands are accepting but 2nd command is working fine but the first command is not working means it's not forwarding. How can i resolve this problem.