[blfs-support] iptables again

akhiezer lfs65 at cruziero.com
Mon Mar 17 11:51:53 PDT 2014


> Date: Mon, 17 Mar 2014 12:55:23 +0000
> From: lfs65 at cruziero.com (akhiezer)
> To: BLFS Support List <blfs-support at linuxfromscratch.org>
> Subject: Re: [blfs-support] iptables again
>
	.
	.
> > > Richard Melville wrote:
> > > > Maybe somebody has the answer to this -- it's only a minor point.
> > > >
> > > > I've set up msmtp and s-nail on a blfs server; I can send email, and
> > > > iptables is not blocking them but neither is it recording the packets
> > > > passed.  When I had this issue before with a different service, changing
> > > > sport to dport resolved it, but not this time.  I've set the ports to 25
> > > > and I've also tried 587. Both work, but still no packets recorded.


(D'you mean the 25/587 wrt mstmp config, or iptables config, or both?)


> > >
> > > What commands are you trying to run?
> > >
> > >    -- Bruce
> > >
> > >
> > I'm sending mail to a colleague via my gmail address with:-
> >
> > cat test.mail |  msmtp -a gmail colleague at company.co.uk


Can you set a command-line verbose flag for msmtp to report & log in more detail what it's doing, just to double-check what port(s) it is actually using in practice.


> >
> > where "gmail" is the name of my account in the .msmtprc file.
> >
> > As I say, the mail delivery works fine with my colleague receiving the
> > mail, and I get a copy in my gmail sent items.  However, iptables -nvL
> > shows "0" in both the pkts and the bytes columns, as if nothing has been
> > sent.  A minor point I know, but all my other traffic (ntp, http, dns, ssh)
> > is recorded by iptables in those two columns.
> >
>
>
> Are you wanting to show incoming or outgoing traffic, or both, or what?
>


(OK, I guess from 'sent' that you mean outgoing traffic ... ).


> Does your firewall log the traffic for the relevant port numbers and for the relevant table (~== traffic-flow direction)?
>


( s|table|table/chain| ).


> Depending on what table you're wanting to see stats for, you might need to use the '-t' flag for iptables to show the stats for the relevant table. You might also find the '--line-numbers' flag useful - e.g. for debugging. (And fwiw, I'd normally use the '-x' flag too).
>


(Long-shot: do try the '-x' - just on the outside chance that omitting it is somehow rounding-down small-values to 0 ).


> If the above don't resolve it, then probably good idea to post your firewall file, plus the literal stats command line (if different from the 'iptables -nvL' posted above).
>


Maybe worth also doing:
--
* log the stats immediately pre- test-message;
* send test email; perhaps also use/send known-size attachment;
* log the stats immediately post- test-message;
* diff the pre-/post- stats.
--
Account for the differences pre-/post-: what caused which traffic; so ideally do the test when non-test network traffic is low/nil; and NB of course that often firewalls are set to only log a subset of traffic (e.g. don't log stuff beyond the first n instances in present connection) - so the byte-amounts logged might be less than the amount sent in your test-email.


Overall, of course, it all depends on what firewall setup you've got in place.



hth,
akh





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