A SYN flood is a DDoS attack that uses all available server resources to render a server unavailable to genuine traffic. The attacker can overflow all open ports on a targeted server machine by continuously sending initial connection request (SYN) packets, causing the targeted device to reply to genuine traffic slowly or not at all.
SYN is a common DDoS attack. Over 80% of DDoS attacks employ the SYN flooding technique, which can cause all of the harm associated with DDoS attacks.
SYN is used to create and establish a connection. This attack also aids in synchronizing sequence numbers between devices.