duplicate connection error

Hello All,
I have one multithreaded server program.Due to fluctuating network, my client is getting disconnected, and after some time i received the new connection from same client, which gets treated as duplicate connection for my server. I have kept my tcp keep alive timer is 10 sec.

Can some one guide me, how can i handle this case? What concept i should use from socket programming for it? I tried shutdown and then close for closing the socket, unfortunately that didn't work.

Thanks,
Mustus