netdev - Re: 2.6.27.8 (+the idr fix) TCP Ack issue

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Date:	Wed, 31 Dec 2008 22:20:46 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Russell King <rmk@....linux.org.uk>
cc:	Netdev <netdev@...r.kernel.org>,
	Ben Hutchings <bhutchings@...arflare.com>
Subject: Re: 2.6.27.8 (+the idr fix) TCP Ack issue

On Wed, 31 Dec 2008, Russell King wrote:

> On Wed, Dec 31, 2008 at 12:38:24PM +0200, Ilpo Järvinen wrote:
> > If you have the dump still at handy, could you add couple of -v -v for
> > tcpdump. It could be that the peer is using bogus seqnos in the
> > duplicate ACK but by default that's not visible for zero sized segs
> > (checked in tcp_validate_incoming in the 2.6.28.7 kernel).
> 
> Is "seqno" another name for the IP ID field?

No, it's a sequence number, there are two sequence number spaces per flow, 
one for each direction (each has a corresponding field in the tcp header). 
For pure ACKs tcpdump won't show the sequence number by default even 
though it's still there...

With tcpdump -n -v -v I get this for pure acks:

...: ., cksum 0x43c0 (correct), 671:671(0) ack 14649 win 36500

That 671:671(0) won't be visible with smaller verbosity.

-- 
 i.