Sorry to bother you again. It turns out my testing was not sufficient and I need an option to bind the listener to a specific interface as well, when I have multiple interfaces in the same (link-local) subnet. Otherwise the Linux kernel tries to send the TCP SYN/ACK on whichever interface was present first even when it received TCP SYN on the other interface. :-\ Therefore a TCP connection cannot be established.
Sorry to bother you again. It turns out my testing was not sufficient and I need an option to bind the listener to a specific interface as well, when I have multiple interfaces in the same (link-local) subnet. Otherwise the Linux kernel tries to send the
TCP SYN/ACK
on whichever interface was present first even when it receivedTCP SYN
on the other interface. :-\ Therefore a TCP connection cannot be established.