On the server both the application and netstat show a connection open. The client however lists no such connection, and the client software is definitely stopped.
I'd already lowered the TCP keepalive settings:
cat /proc/sys/net/ipv4/tcp_keepalive_time 60 cat /proc/sys/net/ipv4/tcp_keepalive_intvl 10 cat /proc/sys/net/ipv4/tcp_keepalive_probes 3
What's causing these connections to remain, even though the client has most definitely disconnected?