netdev - Re: NAT stops forwarding ACKs after PMTU discovery

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Message-ID: <20130819171519.GA4008@cpaasch-mac>
Date:	Mon, 19 Aug 2013 19:15:19 +0200
From:	Christoph Paasch <christoph.paasch@...ouvain.be>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Phil Oester <kernel@...uxace.com>,
	Corey Hickey <bugfood-ml@...ooh.org>,
	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	Linux Netdev List <netdev@...r.kernel.org>,
	netfilter-devel@...r.kernel.org
Subject: Re: NAT stops forwarding ACKs after PMTU discovery

On 19/08/13 - 09:00:31, Eric Dumazet wrote:
> On Mon, 2013-08-19 at 17:33 +0200, Christoph Paasch wrote:
> > Unfortunately, they will hardly go away in the near futur. Rather the
> > opposite is the case.
> > 
> > 
> > If you have a public server running, I would be interested in the count of
> > invalid SACK-blocks received (netstat -s | grep TCPSACKDiscard). This is an
> > indication for such kind of middlebox between your server and the client,
> > implying that these connections cannot benefit from TCP-FastRetransmission
> > and each packet-loss will require an RTO to recover.
> > 
> 
> If the (random) sequence offset is small rather than completely out of
> window, it's going to be hard to detect all problems.

Yes, it is not possible to make it 100% perfect. But considering the size of
the seq-space, the probability is rather low that the SACK-block falls
in-window.

> Show us your patch ;)

Will send it soon. Have to rebase on net-next,... :)
(it's several months ago that I did this)


Christoph
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