Re: Port forwarding with iptables on tunnel interface

[Guido Trentalancia <guido@trentalancia.com>]

Hello again Mike,

On Fri, 2010-02-12 at 11:56 -0800, Mike Wright wrote:
> >> Salve, Guido.  I gave this a verrrry quick glance and off the top of my 
> >> head I think something looks fishy in the POSTROUTING rules.
> >>
> >> In the PREROUTING you are selecting based on the *destination* port.  On 
> >> the return trip shouldn't POSTROUTING use *source* port?
> > 
> > Hold on a second. The originating caller expects a reply on *its 25
> > port*. Therefore my originating port could be everything and usually is
> > an high port (> 1024) different than 25, but the important is that the
> > destination port is 25 because there is the caller waiting a reply. 
> > 
> > Therefore even in the case of SNAT, I am selecting the destination port.
> > 
> > Do you convene with me now ?
> 
> Yes, indeed.  It seems I have my brain in backwards ;D
> 
> Buona fortuna !

You were actually right. The SNAT needs to be done with --sport 25 and
not with --dport 25. But still I cannot get the mail delivered and
actually I cannot see POSTROUTING but only untranslated reply packets...

Any other idea ?

Regards,

Guido