Consider a TCP client and a TCP server running on two different machines. After completing data transfer, the TCP client calls close to terminate the connection and a FIN segment is sent to the TCP server. Server-side TCP responds by sending an ACK, which is received by the client-side TCP. As per the TCP connection state diagram (RFC 793), in which state does the client-side TCP connection wait for the FIN from the server-side TCP?

According to the TCP connection state transition diagram (RFC 793):

1. ESTABLISHED $\xrightarrow{\text{close / send FIN}}$ FIN-WAIT-1: The active closer (client) sends a FIN and enters the FIN-WAIT-1 state, waiting for an ACK of its FIN (or a FIN from the remote side).

2. FIN-WAIT-1 $\xrightarrow{\text{receive ACK}}$ FIN-WAIT-2: Upon receiving the ACK for its FIN segment from the server, the client transitions to the FIN-WAIT-2 state.

3. FIN-WAIT-2: In this state, the client waits for the connection termination request (FIN segment) from the server.

4. FIN-WAIT-2 $\xrightarrow{\text{receive FIN / send ACK}}$ TIME-WAIT: When the server's FIN is received, the client sends an ACK and enters the TIME-WAIT state.

Therefore, the client-side TCP waits for the server's FIN in the FIN-WAIT-2 state (Option D).