TCP connection termination (four-way handshake) in Computer Networks - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the TCP four-way handshake steps

Which sequence correctly describes the four steps in the TCP connection termination process?

A FIN from server, ACK from client, SYN from client, ACK from server

B FIN from client, ACK from server, FIN from server, ACK from client

C ACK from client, FIN from server, ACK from server, FIN from client

D SYN from client, SYN-ACK from server, ACK from client, FIN from server

💡 Hint

Remember the termination starts with a FIN to signal closing.

The TCP four-way handshake for termination involves one side sending a FIN to close its sending side, the other side acknowledges it, then sends its own FIN, and finally the first side acknowledges that FIN.

📋 Factual

intermediate

Role of ACK in TCP connection termination

What is the role of the ACK packet in the TCP four-way handshake termination?

A It carries data to keep the connection alive

B It initiates the connection termination

C It resets the connection immediately

D It acknowledges receipt of the FIN packet from the other side

💡 Hint

Think about what happens after a FIN is sent.

After a FIN is sent to indicate the sender wants to close, the receiver sends an ACK to confirm it received the FIN.

🔍 Analysis

advanced

Why does TCP use a four-way handshake instead of a three-way handshake for termination?

Which explanation best describes why TCP uses a four-step process to terminate a connection?

A Because each side must independently close its sending channel, requiring separate FIN and ACK packets

B Because the connection must be reset twice to ensure no data loss

C Because the server always closes the connection first, then the client follows

D Because the handshake includes an extra SYN packet to confirm termination

💡 Hint

Consider the full-duplex nature of TCP connections.

TCP connections are full-duplex, meaning data can flow both ways independently. Each side must close its sending side separately, so a FIN and ACK are exchanged for each direction, totaling four steps.

❓ Comparison

advanced

Difference between TCP connection termination and reset

Which statement correctly contrasts TCP connection termination with a TCP reset (RST)?

A Both termination and reset use the same four-way handshake process

B Termination resets the connection immediately; reset uses a four-way handshake

C Termination uses a four-way handshake to close gracefully; reset immediately aborts the connection without handshake

D Reset is used only to establish connections; termination is for closing

💡 Hint

Think about graceful vs abrupt connection closing.

Termination allows both sides to finish sending data and close cleanly using the four-way handshake. Reset (RST) immediately aborts the connection, often due to errors or unexpected conditions.

❓ Reasoning

expert

State of TCP connection after first FIN and ACK exchange

After the first FIN is sent by one side and the other side replies with an ACK, what is the state of the connection on the side that sent the FIN?

A It is in FIN-WAIT-2 state, waiting for the other side's FIN

B It is in FIN-WAIT-1 state, waiting for the other side's FIN

C It is CLOSED because it finished termination

D It is ESTABLISHED because connection is still open

💡 Hint

Recall the TCP state transitions during termination.

After sending FIN and receiving ACK, the sender moves to FIN-WAIT-2 state, waiting for the FIN from the other side to complete termination.