From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nils Juergens <ju@isf.rwth-aachen.de>
Subject: Re: How to log what is drop
Date: Thu, 08 Jul 2004 11:38:39 +0200
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On Thu, 08.07.04, Gavin Hamill <gdh@acentral.co.uk> wrote:

> > And I had the following rule:
> > 	Iptables -A FORWARD -j LOG
> >
> > It seems that all connections is logged so it is very difficult to read the
> > log.
> 
> Firstly, do you actually have DROP statements in your ruleset? If so, the LOG 
> statement should appear JUST BEFORE the block of DROP statements. Since 
> ACCEPT or DROP are one-way-streets for packets, you want to LOG just before 
> they get DROPped, but not log any of the ACCEPTed packets.

A very good way to do this is via a special chain "logdrop"

iptables -N logdrop
iptables -A logdrop -j LOG --log-prefix ' log drop '
iptables -A logdrop -j DROP

And then you replace every -j DROP (that you want logged) with -j logdrop.

I think this is mentioned in a part of the netfilter docs.

hth,
Nils