In-depth understanding of TCP three-way handshake: connection reliability and security risks

Table of contents

• preface
• A Review of TCP Introduction and How It Works
• Purpose and steps of TCP three-way handshake
• Possible problems and security risks during the TCP three-way handshake
• Why is the TCP three-way handshake necessary?
• Is it possible to increase or decrease the number of three-way handshakes?
• Similarities and differences between TCP four-way handshake and three-way handshake

preface

        In network communication, TCP (Transmission Control Protocol), as a reliable transmission protocol, is widely used in the Internet and local area networks. TCP ensures reliable transmission of data by establishing a connection, and the TCP three-way handshake is a key step in establishing a connection. This article will deeply discuss the purpose, steps, possible problems and security risks of the TCP three-way handshake to help readers better understand the working mechanism of the TCP protocol.

A Review of TCP Introduction and How It Works

        TCP is a connection-oriented protocol that provides reliable data transmission. It ensures the reliability of data transmission through serial number and confirmation response mechanism. The TCP header contains fields such as source port number, destination port number, serial number, confirmation response number, etc., which are used for data transmission control.

Purpose and steps of TCP three-way handshake

The TCP three-way handshake is the key process of establishing a TCP connection. Its purpose is to ensure that the client and server reach a consensus and establish a reliable connection. Specific steps include:

1. The first handshake (SYN-SENT): The client sends a SYN packet to the server, in which the SYN flag is set to 1, and the client selects an initial sequence number (ISN).
2. The second handshake (SYN-RECEIVED): After receiving the SYN packet sent by the client, the server responds with an ACK packet and its own SYN packet. The ACK packet confirms the receipt of the client's SYN packet and confirms the client's serial number, while the server chooses its own initial serial number.
3. The third handshake (ESTABLISHED): After receiving the server's ACK packet and SYN packet, the client confirms receipt of the server's SYN packet and sends an ACK packet to confirm the server's serial number. After the ACK packet reaches the server, the connection between the server and the client is formally established.

Through the three-way handshake process, the client and the server ensure that both sides have received the handshake package correctly, and can confirm the serial number and establish a connection with each other.

Possible problems and security risks during the TCP three-way handshake

During the TCP three-way handshake, there are some security risks and possible attack methods, including:

1. SYN flood attack: The attacker pretends to be a large number of false IP addresses and sends a large number of SYN packets to the server, occupying server resources and causing the server to fail to process other connection requests normally.
2. TCP connection hijacking: The attacker steals the session information of the TCP connection, intervenes in the process of establishing the connection and obtains the permission of data transmission.

In order to prevent these attacks, some security measures can be taken, such as using firewalls, IDS/IPS systems or limiting the number of concurrent connections.

Why is the TCP three-way handshake necessary?

        The design of the TCP three-way handshake is to ensure that a reliable connection can be established between the client and the server , and to confirm the serial number of data transmission with each other. Through the handshake process, data transmission errors caused by network delay or packet loss can be avoided .

Is it possible to increase or decrease the number of three-way handshakes?

        The TCP three-way handshake is the minimum requirement for establishing a connection and is a widely accepted standard. In practice, increasing or decreasing the number of handshakes may introduce unnecessary complexity or reduce the reliability of the connection . Therefore, changing the number of handshakes is generally not recommended to maintain compatibility with most network devices and applications.

Similarities and differences between TCP four-way handshake and three-way handshake

The TCP four-way handshake is the process of terminating the TCP connection , which corresponds to the three-way handshake process of establishing a connection . The steps of TCP four-way wave include:

1. First wave (FIN-WAIT-1): The connected party sends a FIN packet, indicating that it has completed sending data.
2. The second wave (CLOSE-WAIT): After receiving the FIN packet, the other party sends an ACK packet to confirm receipt of the FIN packet, but it still has data to send.
3. The third wave (FIN-WAIT-2): After the other party finishes sending the data, it sends a FIN packet, indicating that it has also completed sending the data.
4. The fourth wave (TIME-WAIT): After receiving the FIN packet, the connected party sends an ACK packet to confirm receipt of the FIN packet, and enters a TIME-WAIT state, and closes the connection after waiting for a period of time.

  

The process of TCP waving four times is to ensure that both parties have completed the data transmission, and wait for a period of time to ensure that the other party has received its own ACK packet.

Compared with the TCP three-way handshake, the TCP four-way handshake involves the end of data transmission and the termination of the connection, requiring more steps.

in conclusion

        Through an in-depth understanding of the TCP three-way handshake, we can better grasp the working principle of the TCP protocol and the process of establishing a reliable connection. At the same time, understanding possible security risks can help us take corresponding security measures to protect the security of network communications.