Is it possible to route traffic from one port to another on the SAME interface ?

I have an ethernet interface (eth0) that is connected to the internet. Traffic is coming IN on port 5025 and needs to be resend (out) to port 25 on the same interface.

(This is used to connect outlook to my providers smtp server)
Is it also possible to filter on MAC address so only my computer can send data to this port ?

Tnx in advance !

Hi -

I can't imagine *why* you'd want to do this - but you certainly *can*.

FOR EXAMPLE:
1. Have your listener process open *two* sockets.
2. The server thread would call a socket(), listen(),
bind (5025) and accept () ... just like I imagine it's doing now.
3. But you'd *also* open another, second socket for writing out
the data you're reading on input port 5025.
4. You might also want to have this socket bind() to port 25.
And maybe even disable your standard mail daemon (smtp port 25)
from coming up at system boot.

Good luck!

>Traffic is coming IN on port 5025 and needs to be resend (out) to
>port 25 on the same interface.
>my providers smtp server

Outgoing email?
You mean port 25 on a remote computer, not listening on the interface.

You need to be very carefull that you don't leave a mail relay accessable from the internet.


You could do it with iptables or with portfwd
with somthing like this, fill in the numeric ip address of you ISP's mail server.
Change 192.168.0.0/16 if you are using a different range of lan addresses eg 10.0.0.0/8

/*
* mailrelay.cfg
*
* Forward all connections on TCP port 5025 to 1.2.3.4:25 */
tcp { 192.168.0.0/16:5025 { => 1.2.3.4:25 } }
/*
* eof: mailrelay.cfg
*/

Portfwd is somtimes usfull because you can run it without root access, though without root you can't usually listen on ports 1-1024.

>filter on MAC address so only my computer can send data to this port ?

That can probably be done with an iptables rules