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Re: Denial of Service using invalid Content-Length header

From: Adrien de Croy <adrien@qbik.com>
Date: Tue, 21 Jun 2011 10:05:49 +1200
Message-ID: <4DFFC43D.5000407@qbik.com>
To: Willy Tarreau <w@1wt.eu>
CC: Poul-Henning Kamp <phk@phk.freebsd.dk>, Jan Starke <jan.starke@outofbed.org>, ietf-http-wg@w3.org

I think the inference was that some servers will struggle to provide 
service to others when they maintain 30.000 idle connections.

But in the end, I don't see any real difference between sending the POST 
or even just sending nothing.

The server will have some sort of timeout.  It might be a different 
timeout used for waiting for anything vs waiting for a completion of a 
POST message body.

but I think the timeout in general will be long enough for many 
connections to have been initiated.

Things that mitigate that are features like connection rate limiting 
(per source IP), per-IP overall concurrent connection limits etc.


On 21/06/2011 9:56 a.m., Willy Tarreau wrote:
> On Mon, Jun 20, 2011 at 09:41:10PM +0000, Poul-Henning Kamp wrote:
>> In message<20110620211911.GL2897@1wt.eu>, Willy Tarreau writes:
>>> On Mon, Jun 20, 2011 at 05:03:32PM +0000, Poul-Henning Kamp wrote:
>>>> There is no possible timeout value which will both serve slow clients
>>>> in bad connectivity (iPhone4 ?) and prevent DoS attacks.
>>> Yes in practice you can because even with bad connectivity you're generally
>>> interested by covering holes as large as 30-60 seconds,
>> Well your sever may not crash, but it does not serve legitimate
>> traffic either.
> I'm sorry, I don't see your point. Why are you saying that the server does
> not serve legitimate traffic ? It will only break the dead connection but
> still serve all other ones well, that's the point of timeouts.
> Also that's why some protocols with very long sessions implement an
> application-level keep-alive (eg: SSH). That way it's possible to have
> reasonable timeouts (eg. twice the keep-alive interval) without keeping
> dead connections forever.
> Willy

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Received on Monday, 20 June 2011 22:06:26 UTC

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