Which sequence represents the TCP three-way handshake?

Which sequence represents the TCP three-way handshake?

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

Answer: (C)

Understanding how a TCP connection is established using the three-way handshake helps explain why this sequence is correct. The client first sends a segment with the SYN flag to initiate the connection and synchronize sequence numbers. The server replies with a segment that has both the SYN and ACK flags, acknowledging the request and providing its own sequence number. Finally, the client sends a segment with the ACK flag to acknowledge the server’s response and complete the handshake, after which data transfer can begin. Starting with an ACK would imply a connection is already established, which isn’t the case at the outset. A middle segment that is only ACK would not establish synchronization, so the connection wouldn’t be properly set up. A segment that ends with FIN would indicate termination, not initiation, of a connection. FIN is used when closing a connection, not during the handshake.

Understanding how a TCP connection is established using the three-way handshake helps explain why this sequence is correct. The client first sends a segment with the SYN flag to initiate the connection and synchronize sequence numbers. The server replies with a segment that has both the SYN and ACK flags, acknowledging the request and providing its own sequence number. Finally, the client sends a segment with the ACK flag to acknowledge the server’s response and complete the handshake, after which data transfer can begin.

Starting with an ACK would imply a connection is already established, which isn’t the case at the outset. A middle segment that is only ACK would not establish synchronization, so the connection wouldn’t be properly set up. A segment that ends with FIN would indicate termination, not initiation, of a connection. FIN is used when closing a connection, not during the handshake.