How to redirect packets received from one network interface to another network interface?

Question

I am using ubuntu11.10, and I created a tun/tap interface using the following commands

openvpn --mktun --dev tun0
ip link set tun0 up
ip addr add 10.10.10.1/24 dev tun0
route add 10.10.10.1/24 dev tun0

I have another interface there

eth0 10.80.1.87

I wanna redirect packets received from tun0 to eth0. How to do that on top of Ubuntu?

Answer 1

As a complement to the two otherwise good answers, remember that:

• bridging work at link layer ("ethernet level") -- and so configuring a bridge between two interfaces is mostly like wiring them through a (virtual) switch
• forwarding work at network layer ("IP level") -- and so configuring forwarding between two interfaces is like connecting them through a (virtual) router