What is SYN flood?

A SYN flood is a denial-of-service attack that abuses the TCP handshake by sending many connection requests without completing them.

It targets TCP services such as web servers, mail servers, VPN gateways, and load balancers, often causing slow connections or unavailable applications.

How does it work?

In a normal TCP handshake, a client sends SYN, the server replies with SYN-ACK, the client returns ACK, and the session opens. During a SYN flood, attackers generate large numbers of SYN packets, often from spoofed or distributed sources, then never send the final ACK.

The target keeps pending connection records while waiting for completion. As the backlog fills, real users may be delayed or rejected until a firewall, server control, or DDoS mitigation layer filters the traffic.

SYN flood vs DDoS

A SYN flood is one method of causing denial of service. DDoS is the broader attack model where traffic comes from many systems, often a botnet, to overwhelm a target.

In other words, a SYN flood can be part of a DDoS campaign, but not every DDoS attack is SYN-based. UDP floods, HTTP floods, amplification attacks, and fragmented packet attacks use different behaviors and defenses.

How Hexnode supports SYN flood readiness

Hexnode is not a network DDoS scrubbing service, but it helps reduce endpoint-side risk around DDoS activity. Through UEM, teams can maintain endpoint visibility, enforce compliance checks, manage supported firewall-related configuration, deploy patches, restrict unauthorized applications, and trigger remote actions.

This is useful when unmanaged endpoints, kiosks, or IoT-style devices may become botnet participants. Strong endpoint security and configuration hygiene help teams spot abnormal behavior and reduce attack traffic risk.

When should organizations use it?

Organizations should plan for SYN flood protection when they operate public-facing TCP services, customer portals, VPN access, APIs, mail infrastructure, or critical cloud workloads. Controls typically include DDoS protection, rate limiting, SYN cookies, upstream filtering, autoscaling, network monitoring, and incident response runbooks.

They should also review readiness after traffic spikes, unexplained connection failures, botnet alerts, or availability incidents. The priority is preserving service availability while separating attack traffic from legitimate users.