gistfile1.txt

PRIVATE_IFACE=$(ip -4 link show | grep 'ens[0-9]' -o | head -1)
PUBLIC_IFACE=$(ip -4 link show | grep 'ens[0-9]' -o | tail -1)
PRIVATE_SUBNET=$(ip -4 addr show ens4 | grep inet | grep '[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\/[0-9]\+' -o | awk -F\. '{print $1 "." $2 "." $3 ".0"}')
echo "${PRIVATE_SUBNET}" | grep '^172\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.0$' || {
    echo "Invalid private network '${PRIVATE_SUBNET}' must be 172.x.x.x"
    exit 1
}
sysctl -w net.ipv4.ip_forward=1
iptables -A FORWARD --src ${PRIVATE_SUBNET}/24 -i ${PRIVATE_IFACE} -j ACCEPT
iptables -A FORWARD -j DROP
iptables -t nat -A POSTROUTING -o ${PUBLIC_IFACE} -j MASQUERADE