netdev - Re: [PATCH 1/4] netfilter: xt_connlimit: fix daddr connlimit in SNAT scenario

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Message-ID: <alpine.LNX.2.01.1103141310140.27542@obet.zrqbmnf.qr>
Date:	Mon, 14 Mar 2011 13:26:00 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Changli Gao <xiaosuo@...il.com>
cc:	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 1/4] netfilter: xt_connlimit: fix daddr connlimit in SNAT
 scenario

On Monday 2011-03-14 07:50, Changli Gao wrote:

>We use the reply tuples when limiting the connections by the destination
>addresses, however, in SNAT scenario, the final reply tuples won't be
>ready until SNAT is done in POSTROUING or INPUT chain

If I am not mistaken: if you do daddr counting, SNAT is irrelevant.
Consider ruleset
 -t nat -A PREROUTING -p tcp --dport 80 -j DNAT --to 1.2.3.4:80
 -t nat -A PREROUTING -p tcp --dport 443 -j DNAT --to 1.2.3.5:443

The tuple will first be (as per conntrack -L):
 src=home dst=router src=router dst=home
After DNAT:
 src=home dst=router src=1.2.3.4 dst=home

Thus looking at the src of the reply tuple seems correct — at least this 
is what was wanted, counting per stashed servers (=1 customer), not per 
globally visible address.
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