TCP connection termination (four-way handshake) in Computer Networks - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the TCP four-way handshake?

The TCP four-way handshake is used to properly close a TCP connection between two devices, ensuring that both sides have finished sending data and can safely terminate the connection.

beginner

Name the four steps involved in the TCP connection termination process.

The four steps are: 1) FIN sent by the side that wants to close, 2) ACK sent by the other side to acknowledge the FIN, 3) FIN sent by the other side to close its side, 4) ACK sent by the first side to acknowledge the second FIN.

intermediate

Why does TCP use a four-way handshake instead of a simpler method to close connections?

Because TCP connections are full-duplex, each side can send data independently. The four-way handshake allows each side to close its sending channel separately, ensuring no data is lost.

beginner

What does the FIN flag indicate in a TCP segment?

The FIN flag indicates that the sender has finished sending data and wants to close its side of the connection.

intermediate

What state does a TCP connection enter after sending a FIN and before receiving the final ACK?

It enters the FIN_WAIT_1 state, waiting for an acknowledgment from the other side.

Which TCP flag is used to initiate connection termination?

A ACK

B SYN

C RST

D FIN

The FIN flag signals that the sender wants to close its side of the connection.

How many steps are there in the TCP connection termination process?

A 2

B 4

C 5

D 3

TCP connection termination uses a four-step handshake to close both sides properly.

What does the ACK flag do during TCP connection termination?

A Acknowledges receipt of FIN

B Starts the connection

C Resets the connection

D Sends data

ACK acknowledges that the FIN flag was received, confirming the other side's intent to close.

Why can't TCP close the connection with just one FIN and one ACK?

A Because TCP is half-duplex

B Because SYN must be sent first

C Because both sides must close independently

D Because ACK is not reliable

TCP is full-duplex, so each side closes its sending channel separately, requiring two FINs and two ACKs.

After the first FIN is sent and acknowledged, what does the other side do next?

A Sends its own FIN

B Sends data

C Closes the connection immediately

D Sends a RST

The other side sends its own FIN to indicate it is ready to close its sending channel.

Explain the TCP four-way handshake process for connection termination in your own words.

Think about how each side tells the other it is done sending data.

Why is it important for TCP to have a four-step process to close a connection instead of just one step?

Consider how data flows in both directions.