Problema iptables

[pilovis]

# VPN
# Apre una VPN verso una macchina interna
# eth0 192.168.1.5
# eth1 10.0.0.1
# 10.0.0.22 macchina interna che ha il server VPN

iptables -A FORWARD -p gre -d 10.0.0.22 -j ACCEPT
iptables -A FORWARD -p tcp --dport 1723 -d 10.0.0.22 -j ACCEPT
iptables -A PREROUTING -t nat -p gre -d 192.168.1.5 -j DNAT --to-destination 10.0.0.22
iptables -A PREROUTING -t nat -p tcp --dport 1723 -d 192.168.1.5 -j DNAT --to-destination 10.0.0.22:1723