What Is Three Way Handshake Protocol

Three way

What Does Three-Way Handshake Mean?

A three-way handshake is a method used in a TCP/IP network to create a connection between a local host/client and server.

It is a three-step method designed to allow both communicating ends to initiate and negotiate the parameters of the network TCP socket connection at the same time before data such as HTTP and SSH is transmitted.

Multiple TCP socket connections can be transmitted in both directions simultaneously. A three-way handshake is also known as a TCP handshake or SYN-SYN-ACK, and requires both the client and server to exchange SYN (synchronization) and ACK (acknowledgment) packets before actual data communication begins.

In fact, its name originates from the three messages transmitted by TCP before a session between the two ends is initiated.

Refugeictsolution Explains Three-Way Handshake

A three-way handshake is primarily used to create a TCP socket connection to reliably transmit data between devices. For example, it supports communication between a web browser on the client side and a server every time a user navigates the Internet.


As soon as a client requests a communication session with the server, a three-way handshake process initiates TCP traffic by following three steps.

The Three Steps of a Three-Way Handshake

Step 1: A connection between server and client is established

First, a connection between server and client is established, so the target server must have open ports that can accept and initiate new connections. The client node sends a SYN (Synchronize Sequence Number) data packet over an IP network to a server on the same or an external network.

This SYN packet is a random sequence number that the client wants to use for the communication (for example, X). The objective of this packet is to ask/infer if the server is open for new connections.

Step 2: The server receives the SYN packet from the client node

When the server receives the SYN packet from the client node, it responds and returns a confirmation receipt – the ACK (Acknowledgement Sequence Number) packet or SYN/ACK packet. This packet includes two sequence numbers.

The first one is ACK one, which is set by the server to one more than the sequence number it received from the client (e.g. X+1).

The second one is the SYN sent by the server, which is another random sequence number (for example, Y).

This sequence indicates that the server correctly acknowledged the client’s packet, and that is sending its own to be acknowledged as well.

Step 3: Client node receives the SYN/ACK from the server and responds with an ACK packet

The client node receives the SYN/ACK from the server and responds with an ACK packet. Once again, each side must acknowledge the sequence number received by incrementing it by one.

So now it’s the turn of the client to acknowledge the server’s packet by adding one to the sequence number (in this case, Y+1), and resend it to the server.

Upon completion of this process, the connection is created and the host and server can communicate.

All these steps are necessary to verify the serial numbers originated by both sides, guaranteeing the stability of the connection.

Since both hosts must acknowledge the connection parameters of the other side, a missing or out-of-order segment can be quickly detected before the actual data transfer process is initiated.

How does the 3-way handshake work?

The TCP 3-way handshake

TCP uses a three-way handshake to make a reliable connection. The connection is duplex, and the two sides synchronize (SYN) and acknowledge (ACK) with each other. This exchange of four flags takes place in three steps – SYN, SYN-ACK, and ACK

Why 3-way handshake is required?

As such three packets are involved in a full TCP connection initiation process. The three-way handshake is necessary because both parties need to synchronize their segment sequence numbers used during their transmission.

What happens in the three-way handshaking between any two devices?

Actually, TCP uses the 3-way handshake process to establish a connection between two devices before transmitting the data. After the establishment of the connection, the data transfer takes place between the devices

What layer is SYN ACK?

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TCP layer works as tcp Client and sends the tcp syn with a initial sequence number. Sequence number is to maintain the sequencing of messages. Upon SYN received Sever sends the a new syn and ack of received syn to the client, then client sends the ACK to the server for syn received from server.


Known as the “SYN, SYN-ACK, ACK handshake,” computer A transmits a SYNchronize packet to computer B, which sends back a SYNchronize-ACKnowledge packet to A. Computer A then transmits an ACKnowledge packet to B, and the connection is established. See TCP/IP.

TCP message types

SynUsed to initiate and establish a connection. It also helps you to synchronize sequence numbers between devices.
ACKHelps to confirm to the other side that it has received the SYN.
SYN-ACKSYN message from local device and ACK of the earlier packet.
FINUsed to terminate a connection.


  • TCP 3-way handshake or three-way handshake or TCP 3-way handshake is a process which is used in a TCP/IP network to make a connection between server and client.
  • Syn use to initiate and establish a connection
  • ACK helps to confirm to the other side that it has received the SYN.
  • SYN-ACK is a SYN message from local device and ACK of the earlier packet.
  • FIN is used for terminating a connection.
  • TCP handshake process, a client needs to initiate the conversation by requesting a communication session with the Server
  • In the first step, the client establishes a connection with a server
  • In this second step, the server responds to the client request with SYN-ACK signal set
  • In this final step, the client acknowledges the response of the Server
  • TCP automatically terminates the connection between two separate endpoints.

What is the significance of the TCP three-way handshake for applications that utilize TCP as transport protocol?

The importance of the TCP, 3-Way Handshake for applications that utilize TCP as a transport protocol is to ensure a connection is made before transmitting data such as SSH and HTTP.

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