SYN

Synchronize

SYN refers to the SYN flag or SYN packet used in the TCP (Transmission Control Protocol) communication protocol.

TCP is a widely used transport protocol that enables reliable and ordered delivery of data packets over IP networks. When establishing a TCP connection, the client and the server perform a three-way handshake. The SYN flag plays a crucial role in this handshake process.

Here’s a brief overview of how the SYN flag is used:

1. SYN (Synchronize): In the first step of the three-way handshake, the client sends a TCP packet with the SYN flag set to the server. This packet is commonly known as the SYN packet. The SYN flag indicates the client’s intention to initiate a connection with the server.
2. SYN-ACK (Synchronize-Acknowledge): Upon receiving the SYN packet, the server acknowledges the client’s request by sending back a TCP packet with both the SYN and ACK (acknowledge) flags set. This packet is called the SYN-ACK packet. It signifies the server’s agreement to establish a connection.
3. ACK (Acknowledge): In the final step of the handshake, the client responds to the server’s SYN-ACK packet by sending an acknowledgment packet with the ACK flag set. This packet confirms the establishment of the TCP connection.

Using the SYN flag and the three-way handshake, TCP ensures that the client and server agree to establish a connection before exchanging data. This process helps maintain reliable and orderly communication between network devices.

However, the SYN flag can also be exploited by attackers to launch SYN flood attacks, which are a type of DDoS attack. In an SYN flood attack, an attacker sends many SYN packets to a target server without completing the three-way handshake. This overwhelms the server’s resources and can lead to a denial of service for legitimate users.

• Abbreviation: SYN