FreeBSD TCP ignores zero window size

[Darren Reed]

On 4/04/2012 3:17 AM, Andre Oppermann wrote:
> On 03.04.2012 17:38, Darren Reed wrote:
>> On 3/04/2012 11:45 PM, Andre Oppermann wrote:
>>> It's the other way around.  remote.ssh is sending old data
>>> which freebsd82.62922 has already ack'ed.  The sessions seems
>>> to be de-synchronized, perhaps some middle box mucking with
>>> the segments trying to modulate something?
>>
>> I suspect that the ISP is dropping packets and/or applying
>> some other means of throttling the connection. So, yes.
> 
> That doesn't explain it.  The other side is retransmitting data
> we have already received and acknowledged!  There is not
> nothing we can do on our side.  That behavior is totally
> non-compliant.
> 
> The zero-window is not involved in this as it would affect
> FreeBSD sending data, not the other end sending data.
> 
> Can you try to find out what kind of middle-box is mucking
> TCP here on your side and the other side?  It must be some
> device that actively touches the TCP session transiting
> through it.  A router with active queue management (like WFQ
> or RED) is not enough to cause this behavior.
> 
> What is the OS of your remote.ssh?

I should add that given the other end of this is NetBSD
I have also been following up discussion of this behaviour
on their appropriate list too. That discussion can be
found here:

http://mail-index.netbsd.org/tech-net/2012/04/01/msg003203.html

The currently last installment of which is here:
http://mail-index.netbsd.org/tech-net/2012/04/03/msg003216.html

Darren