netdev - Re: NAT stops forwarding ACKs after PMTU discovery

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Date:	Mon, 19 Aug 2013 09:00:31 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Paasch <christoph.paasch@...ouvain.be>
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 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.

Show us your patch ;)



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