We have a board supporting TCP/IP suite. ftp server couldn't be connected twice and hung ftp client. But telnet server works well. Additionally there are two channels in this board. Only channel II has this problem. Now I have mixed information. I trace the code and notice that TCP task received second connect passive message but valid field in TCP struct is NULL and result in connect fail. Finally ftp server always wait message from session layer.

That's an old board, TCP/IP and RTOS we bought before, no support now,and no efficient debug methods. so process is very slow.