Which sequence describes the three steps of the TCP handshake?

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

Answer: (C)

To establish a TCP connection, a three-step handshake is used. The client starts by sending a segment with the SYN flag set to request the connection. The server replies with a segment that has both SYN and ACK flags set, acknowledging the client’s request and providing its own initial sequence number. The client then sends a final segment with the ACK flag to acknowledge the server’s response, completing the handshake. After this exchange, the connection is open and data can be exchanged reliably.

Other sequences don’t fit this process. Starting with SYN and then FIN would be incorrect because FIN is used to close a connection. A sequence that begins with FIN and then SYN is invalid for the handshake. Beginning with an ACK implies the connection is already established, which isn’t the case at the start of a handshake. Hence, SYN, SYN-ACK, ACK is the correct order.