netdev - Re: [PATCH net-next] tcp: be more strict before accepting ECN negociation

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Date:	Fri, 04 May 2012 20:23:35 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Perry Lorier <perryl@...gle.com>,
	Matt Mathis <mattmathis@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Tom Herbert <therbert@...gle.com>,
	Wilmer van der Gaast <wilmer@...gle.com>,
	Dave Täht <dave.taht@...ferbloat.net>,
	Ankur Jain <jankur@...gle.com>
Subject: Re: [PATCH net-next] tcp: be more strict before accepting ECN
 negociation

On Fri, 2012-05-04 at 11:09 -0700, Rick Jones wrote:
> On 05/04/2012 08:14 AM, Eric Dumazet wrote:
> > From: Eric Dumazet<edumazet@...gle.com>
> >
> > It appears some networks play bad games with the two bits reserved for
> > ECN. This can trigger false congestion notifications and very slow
> > transferts.
> >
> > Since RFC 3168 (6.1.1) forbids SYN packets to carry CT bits, we can
> > disable TCP ECN negociation if it happens we receive mangled CT bits in
> > the SYN packet.
> 
> What sort of networks were these?  Any chance it was some sort of 
> attempt to add ECN to FastOpen?

Nothing to do with fastopen.

Just take a look at a random http server and sample all SYN packets it
receives.

Some of them have TOS bits 0 or 1 set, or even both bits set.




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