What is a three-way handshake process?

A three-way handshake process is used in TCP (Transmission Control Protocol) network for the transmission of data in a reliable way between the host and the client.

It’s called a three-way handshake because three segments are exchanged between the server and the client.

  • SYN: The client wants to establish a connection with the server, and sends a segment with SYN(Synchronize Sequence Number) to the server if the server is up and has open ports.
  • SYN + ACK: The server responds to the client request with SYN-ACK signal bits set if it has open ports.
  • ACK: The client acknowledges the response of a server and sends an ACK(Acknowledgment) packet back to the server.

THREE-WAY HANDSHAKE or a TCP 3-way handshake is a process which is used in a TCP/IP network to make a connection between the server and client. It is a three-step process that requires both the client and server to exchange synchronization and acknowledgment packets before the real data communication process starts.
To establish a connection, the three-way (or 3-step) handshake occurs: SYN: The active open is performed by the client sending a SYN to the server. The client sets the segment’s sequence number to a random value A. SYN-ACK: In response, the server replies with a SYN-ACK.

The client SYNchronizes its sequence number to the server. The server ACKnowledges the client’s sequence number, then SYNchronizes its own sequence number. The client then ACKnowledges the server’s sequence number. It’s called a 3-way handshake because there are 3 messages. TCP (Transmission Control Protocol) is a Transport Layer host-to-host protocol for connection-oriented communication between two computers on an IP network. TCP uses a three-way handshake (aka TCP-handshake, three message handshake, and/or SYN-SYN-ACK) to set up a TCP/IP connection over an IP based network.