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

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Date:	Wed, 22 Aug 2012 11:59:57 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alex Bergmann <alex@...lab.net>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jerry Chu <hkchu@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Nandita Dukkipati <nanditad@...gle.com>
Subject: Re: [PATCH 1/1] tcp: Wrong timeout for SYN segments

On Wed, 2012-08-22 at 11:29 +0200, Alex Bergmann wrote:

> Actual 6 SYN frames are sent. The initial one and 5 retries.
> 

first one had a t0 + 0 delay. How can it count ???

> The kernel is waiting another 32 seconds for a SYN+ACK and then gives 
> the ETIMEDOUT back to userspace.
> 
> Do you mean that we have to send another SYN packet after the 3 minutes?
> 

First SYN is not a retransmit

R2 = time_of_last_SYN - time_of_initial_SYN (t0) = 31

If you read RFC it states :

"In particular, R2 for a SYN segment MUST
 be set large enough to provide retransmission of the segment
 for at least 3 minutes."


That means that the last _retransmit_ MUST happen after 180 seconds.

And not :

Send all the restransmits at t0 + 1, then wait 180 seconds before giving
connect() a timeout indication.



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