Alibaba Cloud Developer

Nov 2, 2023 · Fundamentals

When FIN Packets Arrive Out of Order: Uncovering the Linux Kernel’s TCP Handshake Bug

This article investigates a rare TCP four‑handshake disorder where out‑of‑order FIN and ACK packets cause a server to wait for a timeout before closing, detailing packet captures, kernel code analysis, eBPF monitoring, and the discovery that the shutdown() call versus close() triggers the issue.