Lets look at the scenario:

- Linux Box with 2 NICS (eth0 & eth1)
- Connect internet over eth0 and a cable modem
- NAT to eth1 (10.0.0.x)
- Power Book G4 manually configured 10.0.0.2 (default gw - 10.0.0.1)

So far so good.

Now I am running XPlane (a ver nice flight sim for mac os x) + XsquawkBox. I need to install RogerWilco (up and running). But the problem starts here, I need to outside connections reaches the Mac (10.0.0.2) On port 3782. I must create a rule (in iptables, I suppose) that forwards incoming tcp/udp connections on port 3782 to my private network 10.0.0.2. Ok, I am a newbie in iptables conf. Any helps?

Thank you.

try this (on your gateway box):

# iptables -v -t nat -A PREROUTING -i eth0 -p tcp --dport 3782 -j DNAT --to-destination 10.0.0.2:3782
# iptables -v -t nat -A PREROUTING -i eth0 -p udp --dport 3782 -j DNAT --to-destination 10.0.0.2:3782

that should work.

oh actually... it will need to go before any of the reject rules. so either insert it into the script you use that sets up the rules at bootup, or use '-I' (insert) rather than '-A' (add) to put it at the start of the PREROUTING rules.

must be run as root of course.

[in english, it says "if packets recieved from the internet (eth0) are destined for port 3782 and are tcp or udp, then before doing anything else with them, change their destination IP address to 10.0.0.2 and port to 3782"...]

No more no less!!! I have built that rule, but was using -A instead of -I. BTW after I create a new Chain (-N Flag) 2 min past and the chain/rule disapears.

Very much appreciated for your useful help!