iptables -t nat -A PREROUTING -d xxx.xxx.xxx.xxx -p tcp --dport 21-20 -j DNAT --to-destination 192.168.122.25
iptables -I FORWARD -m state -d 192.168.122.25/32 --state NEW,RELATED,ESTABLISHED -j ACCEPT
iptables -t nat -A POSTROUTING -s 192.168.10.10 -p tcp -m multiport --dport 21,50000:51000 -j SNAT --to-destination %YOU_PUBLIC_ADDRESS%
, появляется такая ошибка iptables v1.4.21: unknown option "--to-destination"
Try `iptables -h' or 'iptables --help' for more information.