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Re: iptables, ftp and dnat?



On Fri, Dec 05, 2008 at 03:30:19PM -0700, Robert L. Harris wrote:

[snip]

> >
> >> here is another link
> >> http://www.cyberciti.biz/faq/iptables-open-ftp-port-21/ (again
> > google).
> >
> >
> >> My strength is in itables not ftp (which is the reason for
> > googling :) )
> >
> >> Also anything to do with iptables and firewalls you should
> > probably read
> >> a tutorial on iptables
> >
> 
>   I've read both of those and understand how the ftp works.  I've
> spent the last 2 days googling.
> Unfortunately it's all working now except how to get the iptables data
> connection in passive
> mode working.  I can log in, etc just fine but when I do a "ls" after
> issuing the "passive"
> command it times out.
> 
>   The second example looks good but doesn't handle the DNAT (the ftp
> server is running on
> another machine behind my firewall.

What I do to track down iptables problems is (if you have access to all
3 machines, client server and firewall). Dump on all 3 machines,
something like

tcpdump -pni <eth?> -s 1500 -w /tmp/trace.dmp host <client ip> and host
<server ip>

client and server ip will vary depending on which machine you are on
(natting).

Also just before the drop statement in you iptables chain, put a line
which logs the packets.

These way you can see what is going on and create some rules to fix it.

But maybe another solution is to use a ftp proxy ? (ftp-proxy) - never
used it ? to get around the active passive port problem



> 
> Robert
> 
> 
> 
> - --
> 
> :wq!
> ====================================================================
> Robert L. Harris                     | GPG Key ID: E344DA3B
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> DISCLAIMER:
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