NO SYN ACK reply for SYN

[martinzhang]

In my project, I used MQX and RTCS version is 4.2.02, the problem is:

Sometime, when my system received a TCP SYN package and the system will send out a RST message, the SYN ACK will not reply to that SYN message.

After the remote system retransmit the SYN, my system will reply a SYN ACK message.

I have checked the TCP connection number, in my system, the maximum allowed connection number is 5, when this no SYN ACK happened, the connection number is 3.

Someone can tell me why this happened and how can I fix this issue.

[martinzhang · Accepted solution]

The problem is the setting of backlog in function listen. The backlog :Hint for the RTCS to determine the maximum number of pending established connections per listening socket. In old version, the backlog is 0, and the maximum number of pending established connections is 1 (backlog +1). Incrase this value, problem is sloved.