Re: [lwip-users] at ZeroWindowProbe the response is not ZeroWindowProbeAck

[Thomas Richter (TCD - DE/Dresden)]

Hi Kieran,

Am 17.05.2011 16:23, schrieb Kieran Mansley:
> On Tue, 2011-05-17 at 16:12 +0200, Thomas Richter (TCD - DE/Dresden)
> wrote:
>> The next sequence by the sender is a TCP_ZeroWindowProbe sequence
>> (some
>> infos to TCP Analyze Sequence Numbers with Wireshark:
>> http://wiki.wireshark.org/TCP_Analyze_Sequence_Numbers). But lwIP
>> responses not with a sequence TCP_ZeroWindowProbeAck, it sends a new
>> TCP_ZeroWindow sequence.
> Do you have definitions for things like TCP_ZeroWindowProbeAck?  As far
> as I'm aware the form that a zero window probe should take is not
> defined; it can be anything that will result in an ACK being sent by the
> other end, and I didn't think there was a particular form that the ACK
> to a zero window probe had to take.
Sorry, I have not definitions for the TCP_ZeroWindowProbeAck.
I try to understand the behavior of the communication.
The Wireshark analysis gives me the result: "This frame ACKs a segment
we have not seen (lost?)"

>
> The zero window probe in your case has 1 byte of payload.  lwIP is
> accepting and acknowledging that byte.  As far as I know this is legal. 
Yes, you have right. Thanks for the tip. The TCP_ZeroWindowProbe is in
the first case always "0x00" and in the second case (with lwIP)
different (also sometimes "0x00").

>> Why lwIP reacts different?
> Different implementations of a specification will have different
> behaviours where that behaviour is not defined by the specification.
Sorry, the different behavior is ok.

>> What can I do that the acknowledge number not increases?
> Change the implementation of lwIP.  Out of interest, why do you care
> about this?  
I´m searching for a possibility to continue the way which I have
selected. I have invested in so much time for this project. Now I will
come to an end.

Thomas