Ipchains and smtp rule

From: Mogens Valentin (monz@danbbs.dk)
Date: 11/19/01 

Message-ID: <3BF93982.11D39BA3@danbbs.dk>
Date: Mon, 19 Nov 2001 17:55:30 +0100
From: Mogens Valentin <monz@danbbs.dk>
To: focus-linux <focus-linux@securityfocus.com>
Subject: Ipchains and smtp rule

I don't understand a thing.
I have a mailserver outside a firewall (I'm missing a switch for the
dmz):

  inet ---+--- firewall --- internal net
          +--- mailserver

The policy is deny everything, allow any outgoing, then allow incoming
as per needed service.
Everything works, including simap to the outdoors mailserver (also
running courier-imap), except for sending mail.

Neither
  ipchains -A -p tcp -s 0/0 -d 0/0 smtp -j accept or even
  ipchains -A input -p tcp -i $PUBLICIFC ! -y -j ACCEPT
does the job.

Using /proc/net/* settings, I generally move trafic to high ports.
Tcpdump showed smtp connects to highports, AFAICT. Sure, I may be
mistaken.
I don't remember seeing smtp on highports, any comments?

If I temporarily allow any traffic on all interfaces, smtp works, so the
mailserver is working.

There's a whole bunch of rules, so please ask for what's needed. 

-- 
Regards,
           Mr Dev - Mogens Valentin
    http://www.mrdev.com - mrdev@danbbs.dk
OpenSource Security - Networking - Programming

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