Catching un-DNAT'ed packets

[Pascal Hambourg]

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.