TCP simultaneous open and self connect prevention

Question

TCP standard has \"simultaneous open\" feature.

The implication of the feature, client trying to connect to local port, when the port is from ephemeral range, can o

Answer 1

The actual problem you are having seems to be that while the server is down, something else can use the ephemeral port you expect for your server as the source port for an outgoing connection. The detail of how that happens is separate to the actual problem, and it can happen in ways other than the way you describe.

The solution to that problem is to set SO_REUSEADDR on the socket. That will let you create a server on a port that has a current outgoing connection.

If you really care about that port number, you can use operating specific methods to stop it being allocated as an ephemeral port.