iptables forward one port on same IP

baetmaen · 01-27-2005, 06:01 AM

Hi,

I have a root server with one interface and one static IP.

How would the command (iptables) look to forward one port from the extranl interface (eth0) to another port on localhost:

xxx.xxx.xxx.xxx:25 ---> 127.0.0.1:26

I thought this would work:

Code:

$IPT -A tcp_inbound -p TCP -i eth0  --dport 25 -j FORWARD -d 127.0.0.1 --to-ports 26

but it isn't (where $IPT contains the full path to iptables).

My main problem is: I run a Domino Server on this box and I don'T want him to use 25 since postfix is running there to send me notifications from my cron scripts and so on. So I switched domino's port to 26 and now I want to forward incoming connections on port 25 to localhost port 26 ;(

How should the line look like ? To be honest, I created that script with an iptables script generator and added this line on my own. But I canÄt find the error here (The parameters like --dport --to-port and -d are from the man page)

Joerg

zsoltrenyi · 01-27-2005, 06:56 AM

the port forwarding is made with -j DNAT in the prerouting chain
so the rule should look like this:
iptables -A PREROUTING -p tcp -i eth0 --dport 25 -j DNAT --to-destination 127.0.0.1:26

baetmaen · 01-27-2005, 08:47 AM

Quote:

Originally posted by zsoltrenyi
the port forwarding is made with -j DNAT in the prerouting chain
so the rule should look like this:
iptables -A PREROUTING -p tcp -i eth0 --dport 25 -j DNAT --to-destination 127.0.0.1:26

For some reason this is not helping ;(

I can still see a dropped message in the syslog. But for further help you might also need more information, right ?

joerg