netdev - Re: DDoS attack causing bad effect on conntrack searches

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Date:	Fri, 23 Apr 2010 15:57:41 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Jesper Dangaard Brouer <hawk@...u.dk>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	Changli Gao <xiaosuo@...il.com>, hawk@...x.dk,
	Linux Kernel Network Hackers <netdev@...r.kernel.org>,
	netfilter-devel@...r.kernel.org,
	Paul E McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: DDoS attack causing bad effect on conntrack searches

Jesper Dangaard Brouer wrote:
> On Fri, 23 Apr 2010, Patrick McHardy wrote:
> 
>> That sounds like a good idea. But lets what for Jesper's test results
>> before we start fixing this problem :)
> 
> I will first have time to perform the tests Monday or Tuesday.
> 
> BUT I have just noticed there seems to be a corrolation between
> conntrack early_drop and searches.  I have upload a new graph:
> 
>  http://people.netfilter.org/hawk/DDoS/2010-04-12__001/conntrack_early_drop002.png

I guess that's somewhat expected when your conntrack table is full
and all you're seeing is new connection setup attempts.

First you have a search for an existing conntrack, then it attempts
to create a new one and tries to early_drop and old one.
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