Java network server and TIME_WAIT

Question

I have run into a problem with a network server that receives signals from devices my company produces. The device will occasionally reuse the source port that it had just

Answer 1

Building on Nikolai's answer,

Socket s;
...
s.setSoLinger(true,0);

would be the equivalent in Java.

EDIT: Another thing you might like to look at would be setReuseAddress(true);

Answer 2

The old not-recommended trick to avoid TIME_WAIT is to set SO_LINGER socket option to { 1, 0 } - the close then sends RST instead of doing normal flush/four-way exchange sequence, thus avoiding the TIME_WAIT all together (be warned - you might lose tail of what you still have in the send buffer.) I can't comment on whether this could be done in Java though.

EDIT: Can you confirm with tcpdump that the clients really reuse source port numbers? If not, this might just be the classic case for SO_REUSEADDR listening socket option as Jon pointed out.

Answer 3

The server is ignoring the SYN packets from the client because it cannot distinguish between those for a new session using the old source port and retransmissions from the old session. If you circumvent the TIME_WAIT state on the server, by setting the system timer interval for aging out TIME_WAIT state entries in the control block table, then how will your server properly ignore SYN retransmissions for sessions that have already terminated?