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diff --git a/health/guides/tcp/1m_tcp_syn_queue_drops.md b/health/guides/tcp/1m_tcp_syn_queue_drops.md new file mode 100644 index 00000000..c29d86d7 --- /dev/null +++ b/health/guides/tcp/1m_tcp_syn_queue_drops.md @@ -0,0 +1,22 @@ +### Understand the alert + +This alert indicates that the average number of SYN requests dropped due to the TCP SYN queue being full has exceeded a specific threshold in the last minute. A high number of dropped SYN requests may indicate a SYN flood attack, causing the system to become unresponsive to legitimate traffic. + +### Troubleshoot the alert + +1. **Monitor incoming traffic**: Analyze the incoming network traffic to determine if there is a sudden surge in SYN requests, which might indicate a SYN flood attack. Use tools like `tcpdump`, `iftop`, or `nload` to monitor network traffic. + +2. **Check system resources**: Inspect the system's CPU and memory usage to ensure there are enough resources available to handle incoming connections. High resource usage might lead to dropped SYN requests. + +3. **Enable SYN cookies**: If the traffic is legitimate, consider enabling SYN cookies to help mitigate the impact of a SYN flood attack, as described in the provided guide above. + +4. **Adjust SYN queue settings**: Increase the SYN queue size by adjusting the `net.core.somaxconn` and `net.ipv4.tcp_max_syn_backlog` sysctl parameters. Make sure to set these values according to your system's capacity and traffic requirements. + +5. **Implement traffic filtering**: Use traffic filtering techniques such as rate limiting, IP blocking, or firewall rules to mitigate the impact of SYN flood attacks. + +### Useful resources + +1. [SYN packet handling](https://blog.cloudflare.com/syn-packet-handling-in-the-wild/) +2. [SYN Floods](https://en.wikipedia.org/wiki/SYN_flood) +3. [SYN Cookies](https://en.wikipedia.org/wiki/SYN_cookies) +4. [ip-sysctl.txt](https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt) |