Responding to "Possible SYN flooding on port"

When managing servers, encountering a system log warning like "Possible SYN flooding on port" can be alarming. This blog post breaks down what this message means, its implications, and how to handle it effectively.

What is SYN Flooding?

SYN flooding is a cyber attack aimed at disrupting service by overwhelming a server with connection requests. It exploits the TCP connection sequence, known as the three-way handshake.

Understanding the Log Message "Possible SYN flooding on port"

Consider this log message: "request_sock_TCP: Possible SYN flooding on port 1.2.3.4:443. Sending cookies."

Here's what each part signifies:

• request_sock_TCP: Indicates a TCP connection request.
• Possible SYN flooding: Suggests a potential SYN flood attack.
• Port 1.2.3.4:443: Specifies the affected port and IP address.
• Sending cookies: Shows the server's defense response.

The Role of "Sending Cookies"

In response to SYN flooding, Linux employs a method called 'SYN cookies'. These are not actual cookies but are special data packets used to confirm the legitimacy of connection requests.

Why Worry About SYN Flooding?

The dangers of SYN flooding include:

• Reduced server performance.
• Denial of service to legitimate users.
• Potential server downtime.

How to Secure Your Server

Protecting your server requires several strategic steps:

• Activate SYN Cookies: This essential feature helps mitigate flood impacts.
• Increase SYN Queue Size: This allows your server to handle more connection requests simultaneously.
• Restrict Connections Per IP: This limits the number of connections any single IP can attempt.
• Deploy Firewalls: Firewalls can preemptively block suspected malicious traffic.
• Monitor Traffic: Regular analysis helps identify and respond to threats promptly.
• Implement External DDoS Protection: Services such as Akmatori provide robust protection against DDoS attacks, helping to safeguard your server efficiently.

Using Akmatori for Enhanced Protection

Another robust option for securing your servers is Akmatori, a globally distributed TCP/UDP load balancer. Thanks to its worldwide distribution and anti-DDoS capabilities, Akmatori can effectively prevent SYN floods by distributing traffic across multiple servers. This not only dilutes the impact of any single attack but also ensures that your server infrastructure remains resilient and operational under adverse conditions.

Conclusion

"Possible SYN flooding on port" is a critical alert that administrators should not ignore. By understanding and implementing effective security measures, you can safeguard your servers against such disruptive attacks.