# SYN Flood Attacks: How TCP Handshake Exploitation Overwhelms Your Servers

> A SYN flood exhausts your server's connection state table in seconds — no bandwidth required. We break down the mechanics and the mitigations that actually work.

- Category: Attack Analysis
- Author: Akarguard Team, Security Engineering
- Published: Sep 13, 2026
- Canonical: https://akarguard.net/blog/syn-flood-attack

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TCP was never designed with adversaries in mind. The three-way handshake — SYN, SYN-ACK, ACK — is fundamental to reliable communication, but it creates a vulnerability: a server must allocate state for each half-open connection before the client acknowledges. SYN floods exploit exactly this.

## How a SYN Flood Works

The attacker sends a flood of TCP SYN packets with spoofed source IPs. The server responds to each with a SYN-ACK and waits for the final ACK — which never comes because the source address is fake. The server's connection state table fills up. Legitimate connections are refused. Service is down.

- Requires no bandwidth amplification — 100Mbps of SYN traffic can take down a server handling gigabits of normal load.
- Spoofed IPs make blacklisting ineffective at the server level.
- Attack tools generate millions of unique fake source IPs per second.

## Mitigation Techniques

- SYN cookies: server encodes state into the sequence number, removing the need to store half-open connections.
- Enable SYN cookies and tune your connection backlog at the origin and its firewall.
- Absorb the raw packet flood upstream — at your host or transit provider's network, which is where a stateless flood is actually stopped.
- Hide your origin IP behind a reverse proxy so a flood aimed at your server has no target to reach.

> **Where a reverse proxy helps — and where it doesn't** — Hiding your origin behind Akarguard means a SYN flood pointed at your old server IP hits nothing. But this is origin-hiding, not L4 scrubbing: a volumetric flood against the proxy's own address is a network-capacity question for the upstream provider. Akarguard is a Layer 7 (application-layer) service, not a volumetric scrubber.

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Source: Akarguard Security Blog (https://akarguard.net/blog). Akarguard provides DDoS protection: traffic is proxied through our edge, attack traffic is filtered, and clean traffic reaches your origin. Reuse of this article with attribution and a link to the canonical URL is permitted.