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Re: Catching un-DNAT'ed packets

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Subject: Re: Catching un-DNAT'ed packets
From: Pascal Hambourg <pascal.mail@plouf.fr.eu.org>
Date: Tue, 26 Dec 2006 12:09:32 +0100
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Hello,

Pokotilenko Kostik a écrit :

Is it possible to catch un-DNAT'ed packets with iptables' -j ULOG
target?

I'm afraid no.

Where does the un-DNAT occurs and is there table/chain that is
processed after un-DNAT?

In 2.4 kernels, when DNAT occurs in the PREROUTING chain, un-DNAT occurs at the same place as (and in place of) the POSTROUTING chain of the 'nat' table, and there is no chain after it. In 2.4 kernels >= 2.4.19, when DNAT occurs in the OUTPUT chain, un-DNAT occurs after the INPUT chain of the 'filter' table, and there is no chain after it either. I suppose it has not changed in 2.6 kernels.

The problem I have is that replay packets got catched with real source
address, not the one the client has initially connected to. I was
catching replay packets in mangle/POSTROUTING.

The POSTROUTING chain of the 'mangle' table is just before the un-DNAT place.


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