Windows TCP Handshake Problem

Question

I am trying to create a TCP connection from an embedded controller to a Windows Vista server. I am writing the Windows server part of the application.

When the controller attempts to connect, it can take many attempts to establish the connection. I have used Wireshark to debug the problem and it appears that the Windows TCP stack is not following the correct handshake protocol.

Wireshark dump:

"No","Time","Source","Destination","Protocol","Info"

Try1:

"39","9.025322","10.0.0.252","10.0.0.92","TCP","49153 > xinuexpansion4 [SYN] Seq=0 Win=127 Len=0"

"40","9.025377","10.0.0.92","10.0.0.252","TCP","xinuexpansion4 > 49153 [ACK] Seq=1 Ack=1 Win=2048 Len=0"

"47","10.031750","10.0.0.252","10.0.0.92","TCP","49153 > xinuexpansion4 [RST] Seq=0 Win=127 Len=0"

Try 2:

"55","12.193941","10.0.0.252","10.0.0.92","TCP","49154 > xinuexpansion4 [SYN] Seq=0 Win=127 Len=0"

"56","12.194045","10.0.0.92","10.0.0.252","TCP","xinuexpansion4 > 49154 [ACK] Seq=1 Ack=1 Win=2048 Len=0"

"57","13.200431","10.0.0.252","10.0.0.92","TCP","49154 > xinuexpansion4 [RST] Seq=0 Win=127 Len=0"

Try 3:

"67","18.529871","10.0.0.252","10.0.0.92","TCP","49156 > xinuexpansion4 [SYN] Seq=0 Win=127 Len=0"

"68","18.529957","10.0.0.92","10.0.0.252","TCP","xinuexpansion4 > 49156 [SYN, ACK] Seq=0 Ack=1 Win=8192 Len=0 MSS=1460"

"69","18.536318","10.0.0.252","10.0.0.92","TCP","49156 > xinuexpansion4 [ACK] Seq=1 Ack=1 Win=127 Len=0"

10.0.0.252 is the controller initiating the connection, 10.0.0.92 is the Windows PC.

As I understand it, the correct sequence is SYN, SYN+ACK, SYN. What I get most of the time is SYN, ACK, RST (i.e. Windows is responding with ACK rather than SYN+ACK). In the above dump it shows 3 connection attempts, the 3rd one works.

Is there anything I can do to 'fix' Windows so that it responds correctly ?

EDIT - 2 packet captures

http://tinyurl.com/33bvyxk shows the embedded controller taking 4 attempts to connect.

http://tinyurl.com/2cd6klr shows the windows client connecting and disconnecting twice without problem.

Answer 1

while the handshake is failing, this does follow the protocol. RST is allowed to reset the connection as part of the protocol. The question is, why is the reset ocurring? Is there a system between the two machines, whcih is sending the reset? If you run botht he server and the client on the same system, do you still get the reset (this would suggest a bug in your code)? if you run the server on a different OS, in the same network jack as the Windows server, do you see the RST?

Answer 2

Have you tried connecting to your Vista server from a client running a full OS like Windows or Linux, using say telnet? On Linux at least you can specify a TCP port number to connect to on the command line, and see whether that can make a connection to your Vista server or not.

One possibility to check: Is the Vista server running some kind of firewall that prevents the connection from occurring?