linux-kernel - Re: [PATCH 1/1] tcp: Wrong timeout for SYN segments

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Message-ID: <1346230305.2522.15.camel@edumazet-glaptop>
Date:	Wed, 29 Aug 2012 01:51:45 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"H.K. Jerry Chu" <hkjerry.chu@...il.com>
Cc:	Alexander Bergmann <alex@...lab.net>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] tcp: Wrong timeout for SYN segments

On Tue, 2012-08-28 at 21:34 -0700, H.K. Jerry Chu wrote:

> IMHO 31secs seem a little short. Why not change it to 6 as well because 63
> secs still beats 93secs with 3sec initRTO and 5 retries.
> 
> Jerry
> 

My rationale was that such increase were going to amplify SYN attacks
impact by 20% (if we count number of useless SYNACK sent)

If the active side sends SYN packets for 180 seconds, do we really want
to also send SYNACKS for additional 100 seconds ?

Sure, RFC numbers are what they are, but in practice, I doubt someone
will really miss the extra SYNACK sent after ~32 seconds, since it would
matter only for the last SYN attempted.



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