The establishment of a TCP connection involves a negotiation called three-way handshake.

The TCP three-way handshake is the foundational mechanism used to establish a reliable connection between two devices. The sequence is as follows:

The client sends a SYN (synchronize) packet to the server to initiate the connection.

The server replies with a SYN-ACK (synchronize-acknowledge) packet.

The client sends an ACK (acknowledge) packet back to the server.

Therefore, the connection starts with a SYN packet from the client.