iptables forwarding between two interface

Solution 1:

First, to enable hosts connecting on your private interface to go out to the internet, you don't need bridging the interfaces, you need to route packets coming in on one interface, to the other one, where they go out to the wild.

To do that, you only need to:

1. Enable forwarding on your linux box:
2. Allow specific (or all of it) packets to traverse your router
3. As someone stated, as netfilter is a stateless firewall, allow traffic for already established connections

4. Change the source address on packets going out to the internet

   echo 1 > /proc/sys/net/ipv4/ip_forward
   iptables -A FORWARD -i wlan1 -o wlan0 -j ACCEPT
   iptables -A FORWARD -i wlan0 -o wlan1 -m state --state ESTABLISHED,RELATED \
            -j ACCEPT
   iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
   

That should do it.