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Message-ID: <471E756E.3070008@tmr.com>
Date: Tue, 23 Oct 2007 18:27:58 -0400
From: Bill Davidsen <davidsen@....com>
To: Al Boldi <a1426z@...ab.com>
CC: Valdis.Kletnieks@...edu, Patrick McHardy <kaber@...sh.net>,
netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
linux-net@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFD] iptables: mangle table obsoletes filter table
Al Boldi wrote:
> Valdis.Kletnieks@...edu wrote:
>> On Sat, 20 Oct 2007 06:40:02 +0300, Al Boldi said:
>>> Sure, the idea was to mark the filter table obsolete as to make people
>>> start using the mangle table to do their filtering for new setups. The
>>> filter table would then still be available for legacy/special setups.
>>> But this would only be possible if we at least ported the REJECT target
>>> to mangle.
>> That's *half* the battle. The other half is explaining why I should move
>> from a perfectly functional setup that uses the filter table. What gains
>> do I get from doing so? What isn't working that I don't know about? etc?
>>
>> In other words - why do I want to move from filter to mangle?
>
> This has already been explained in this thread; here it is again:
>
> Al Boldi wrote:
>>>> The problem is that people think they are safe with the filter table,
>>>> when in fact they need the prerouting chain to seal things. Right now
>>>> this is only possible in the mangle table.
>>> Why do they need PREROUTING?
>> Well, for example to stop any transient packets being forwarded. You could
>> probably hack around this using mark's, but you can't stop the implied
>> route lookup, unless you stop it in prerouting.
>
> Basically, you have one big unintended gaping whole in your firewall, that
> could easily be exploited for DoS attacks at the least, unless you put in
> specific rules to limit this.
>
Well... true enough on a small firewall machine with a really fast link,
maybe. I like your point about efficiency better, it's more logical,
like putting an ACCEPT of established connections before a lot of low
probability rules. The only time I have seen rules actually bog a
machine was when a major ISP sent out a customer "upgrade" with a bug
which caused certain connections to be SYN-SYN/ACK-RST leaving half open
sockets. They sent out 160k of them and the blocking list became very
long as blocking rules were added.
> Plus, it's outrageously incorrect to accept invalid packets, just because
> your filtering infrastructure can only reject packets after they have been
> prerouted.
>
As long as the filter table doesn't go away, sometimes things change
after PREROUTING, like NAT, and additional rules must be used.
--
Bill Davidsen <davidsen@....com>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot
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