Which sequence of messages is exchanged in the TCP three-way handshake?

• A. SYN, SYN-ACK, ACK
• B. SYN, ACK, FIN
• C. ACK, SYN, SYN-ACK
• D. SYN, FIN, ACK

Answer: (A)

The sequence starts with a request to open a connection, using a SYN to indicate the desire to establish a session and to propose an initial sequence number. The next step from the other side combines acknowledgment and its own proposal of an initial sequence number with a SYN-ACK, showing it received the request and is ready to proceed. The final step is the client sending an ACK to acknowledge the server’s ISN, which completes the handshake and establishes a connection for data transfer. The other sequences don’t fit because they either attempt to terminate a connection with FIN, or begin with an ACK before any SYN, which doesn’t set up a connection properly.