What Are a SYN Flood Attack and an ACK Flood Attack?

A SYN flood attack is a typical denial of service (DoS) attack. Utilizing the loop hole in the Transmission Control Protocol (TCP), the attacker sends a huge number of forged TCP connection requests to the target to exhaust its resources (fully loaded CPU or insufficient memory). Consequently, the target fails to respond to normal connection requests.

An ACK flood attack works in a similar mechanism as a SYN flood attack.

An ACK flood attack is when an attacker attempts to overload a server with TCP ACK packets. Like other DDoS attacks, the goal of an ACK flood is to deny service to other users by slowing down or crashing the target using junk data. The targeted server has to process each ACK packet received, which uses so much computing power that it is unable to serve legitimate users.