[Gennadi]

modprobe ip_nat_irc
iptables -t nat -A PREROUTING -i ppp0 -p tcp --dport 6667 -j DNAT --to-destination 192.168.1.2
iptables -t nat -A POSTROUTING -o eth0 -p tcp --dport 6667 -j SNAT --to-source $LAN_IP
iptables -A FORWARD -i ppp0 -m state --state NEW -p tcp -d 192.168.1.2 --dport 6667 -j ACCEPT