Port forwarding doesn't work

[Beju]

Hello,
I need help in setting up a port forwarding on my server, or more precisely, I need a way to check what is happening with the packets sent on the forwarded port, since they seem to vanish inside the server

[Ziplock]

What firewall software are you using? iptables? or something else. What are you trying to achieve? What distro? What's not working?

[Beju]

Yes, I'm using iptables. Basicaly I need to do port forwarding, i.e. make local server visible from the outside What doesn't work is that the packets are visible on the WAN interface, but not on the LAN interface.

[Ziplock]

OK, I am assuming at this point that you have set up the firewall correctly. Have you turned on forwarding:

echo "1" > /proc/sys/net/ipv4/ip_forward

This will need to be done every time you boot.

[Beju]

Well, that's the problem... I don't know how to set up iptables for port forwarding Or maybe I know, but it doesn't work. Yes, the forwarding is on.

[Lazydog]

You need to use DNAT for this.

iptables -t nat -A PREROUTING -p tcp -d 15.45.23.67 --dport 80 -j DNAT --to-destination 192.168.1.1

Here is a TUTORIAL for iprtables that should help you

[Beju]

Thanks for the tutorial I have already read many things about DNAT, but the rule You posted just doesn't work, I don't know why :/

[Lazydog]

Weel you have to ensure packets that are heading back are also NAT'ed.
Do you have this setup? something like this:

iptables -A POSTROUTING -o eth0 -j MASQUERADE

Provided eth0 is your external facing interface?

If this isn't working then maybe posting your rules we can better help you.

[Beju]

Weel you have to ensure packets that are heading back are also NAT'ed.

Are You sure it's necessary? Isn't the DNAT responsible also for connection tracking? Besides that, I think my problem lies somewhere else: I don't know why NONE of the packets I'm sending reaches the DNAT'ed in-LAN server, moreover NONE of them even leaves the firewall internal LAN interface.

But I'll try that anyway, thanks