Re: NAT FROM public ip TO public ip

[Igor Tsinman <igort@go-wlan.com>]

Mario Ohnewald wrote:

>Hello List!
>
>This is a real easy question, but i will explain it in detail so that you
>know what i am on about ;)
>
>I have two internet boxes, both have only one nic.
>Box A is my root box.
>Box B is a ftp server (where i am not admin, but i have an ftp account).
>
>Both, Box A and B have a public ip address.
>You can NOT access the ftp server from the outside.
>ONLY Box A can connect to that ftp server (Box B).
>
>So i though i could simply nat a connection through my Box A, to Box B.
>If i connect from the real bad world, to my Box A, port 2121. Box A could
>forward/NAT that to the internal ftp box.
>
>I have tried it with this rule:
>$IPT -t nat -A PREROUTING -i eth0 -p tcp -d 123.123.123.123 -m helper
>--helper ftp-2121 -j DNAT --to-destination 123.123.123.111
>
>and
>
>modprobe ip_conntrack_ftp ports=21,2121
>
>
>But it looks like its not working.
>I did a tcpdump -i eth0 -n host 123.123.123.111
>
>
>And no packages where transfered to the ftp box (123.123.123.111).
>Any idea why? Am i going the right way at all?
>
>Thanks, Mario
>
>  
>
You have to add an additional rule:
$IPT -A FORWARD -p tcp -i eth1 -d 23.123.123.123 --dport 2121 -j ACCEPT

For this example, eth0 is external and eth1 is internal.



Cheers,
Igor Tsinman

igort@gonetworks.com