netdev - Re: TCP being hoodwinked into spurious retransmissions by lack of timestamps?

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Message-ID: <532CB4D0.50403@hp.com>
Date:	Fri, 21 Mar 2014 14:53:20 -0700
From:	Rick Jones <rick.jones2@...com>
To:	John Heffner <johnwheffner@...il.com>
CC:	Netdev <netdev@...r.kernel.org>
Subject: Re: TCP being hoodwinked into spurious retransmissions by lack of
 timestamps?

On 03/03/2014 07:22 PM, John Heffner wrote:
> Running with such a large window scale and no timestamps (PAWS
> protection) is generally not a great idea, but I don't think is part
> of the issue here.
>
> If you look where things really go wrong, the receiver is sending
> anomalous SACK blocks that will trigger the SACK renege handling path.
>   Reneging triggers go-back-n behavior, so we see the spurious
> retransmits from there on.

What triggers go-back-n when SACK is not in use?  I ask because at least 
once I have seen the same sort of thing without SACK enabled on the 
connection.  The total quantity of retransmissions is roughly the same, 
but spread-out - looks like cwnd shrinks considerably and re-grows in 
the no-SACK case.  Not sure I still have that trace though :(

rick jones
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