nat.sh

#!/bin/bash -x

IPFRDCTL=/proc/sys/net/ipv4/ip_forward

WANNIC=wlan0
LANNIC=eth0

if [[ -f "${IPFRDCTL}" ]]
        then
        echo 1 > "${IPFRDCTL}"
        else
        echo "need ip_forward in kernel"
        exit 0
fi

DAEMON=iptables

        ${DAEMON} -F

        ${DAEMON} -I INPUT -i ${LANNIC} -j ACCEPT
        ${DAEMON} -I INPUT -i ${WANNIC} -p all -m state --state RELATED,ESTABLISHED -j ACCEPT
        ${DAEMON} -t nat -A POSTROUTING -o ${WANNIC} -j MASQUERADE
        ${DAEMON} -A FORWARD -i ${WANNIC} -o ${LANNIC} -m state --state RELATED,ESTABLISHED -j ACCEPT
        ${DAEMON} -A FORWARD -i ${LANNIC} -o ${WANNIC} -j ACCEPT

echo "NAT from private:${LANNIC} to public:${WANNIC}"