How Linux’s SYNPROXY Shields Against SYN Flood DoS Attacks
The article explains how the Linux kernel’s SYNPROXY feature, introduced in version 3.13, effectively mitigates SYN flood DoS attacks by acting as a gateway, validating handshake cookies, and dramatically reducing kernel soft‑IRQ load during testing on Debian and SLES‑12.
DoS attacks remain a persistent problem; while commercial firewalls and load‑balancing gateways can mitigate them, attackers often favor the cheap x86 + GNU/Linux combination.
Linux kernel 3.13 introduced a new SYNPROXY feature, a connection‑tracking based netfilter extension. It marks incoming client SYN packets as UNTRACKED and forwards them to the iptables "SYNPROXY" target (similar to ACCEPT, NFQUEUE, DROP). The kernel then acts like a gateway, completing the TCP three‑way handshake with the client. Only after the final ACK’s cookie is verified does the packet proceed to the actual destination.
Data from Jesper Dangaard Brouer shows SYNPROXY is highly effective against SYN‑FLOOD DoS attacks. The author tested SYNPROXY on Debian and SLES‑12‑beta2 using hping3 and Metasploit. With SYNPROXY enabled, ksoftirq usage dropped from about 8 % to under 3 %.
Signed-in readers can open the original source through BestHub's protected redirect.
This article has been distilled and summarized from source material, then republished for learning and reference. If you believe it infringes your rights, please contactand we will review it promptly.
MaGe Linux Operations
Founded in 2009, MaGe Education is a top Chinese high‑end IT training brand. Its graduates earn 12K+ RMB salaries, and the school has trained tens of thousands of students. It offers high‑pay courses in Linux cloud operations, Python full‑stack, automation, data analysis, AI, and Go high‑concurrency architecture. Thanks to quality courses and a solid reputation, it has talent partnerships with numerous internet firms.
How this landed with the community
Was this worth your time?
0 Comments
Thoughtful readers leave field notes, pushback, and hard-won operational detail here.