netdev - Re: NAT stops forwarding ACKs after PMTU discovery

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Message-ID: <20130819204307.GC4008@cpaasch-mac>
Date:	Mon, 19 Aug 2013 22:43:07 +0200
From:	Christoph Paasch <christoph.paasch@...ouvain.be>
To:	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Corey Hickey <bugfood-ml@...ooh.org>,
	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 - 22:13:59, Jozsef Kadlecsik wrote:
> On Mon, 19 Aug 2013, Eric Dumazet wrote:
> 
> > On Mon, 2013-08-19 at 15:49 +0200, Christoph Paasch wrote:
> >
> > > It's a TCP-patch, that interprets duplicate-acks with invalid SACK-blocks as
> > > duplicate acks in tcp_sock->sacked_out.
> > 
> > Yeah, but here, this is conntrack who is blocking the thing.
> > 
> > TCP receiver has no chance to 'fix' it.
> > 
> > See conntrack is one of those buggy middle box as well.
> > 
> > So if you want to properly handle this mess, you'll also have to fix
> > conntrack.
> 
> I beg you pardon: why conntrack should be relaxed, when it is expected
> to do more strict TCP checkings (RFC5961, Section 5.).

There is no mention of SACK in this RFC.
The duplicate ACKs with invalid SACK-blocks are valid with respect to
RFC5961, Section 5.

Actually, no RFC says that dup-ACKs with invalid SACK-blocks should
be discarded.


Cheers,
Christoph

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