networking protocol_error ai_generated partial

TCP: challenge ACK storm detected on port 443 from 10.0.0.2

ID: networking/tcp-challenge-ack-storm

Also available as: JSON · Markdown · 中文
80%Fix Rate
85%Confidence
1Evidence
2024-03-15First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
Linux kernel 5.15+ active — — —
Linux kernel 6.1+ active — — —
Linux kernel 6.8+ active — — —

Root Cause

A TCP challenge ACK storm occurs when a host receives a flood of out-of-window segments, triggering repeated challenge ACK responses that can overwhelm the sender and degrade network performance.

generic

中文

TCP 挑战 ACK 风暴发生在主机收到大量窗口外段时，触发重复的挑战 ACK 响应，可能淹没发送方并降低网络性能。

Official Documentation

https://www.kernel.org/doc/html/latest/networking/tcp-challenge-ack.html

Workarounds

  1. 80% success Temporarily increase the challenge ACK limit to reduce storm impact: sysctl -w net.ipv4.tcp_challenge_ack_limit=1000 
    Temporarily increase the challenge ACK limit to reduce storm impact: sysctl -w net.ipv4.tcp_challenge_ack_limit=1000
  2. 85% success Identify and fix the source of out-of-window segments by checking for asymmetric routing or packet reordering using tcpdump: tcpdump -i eth0 'tcp and port 443' -w capture.pcap, then analyze with Wireshark. 
    Identify and fix the source of out-of-window segments by checking for asymmetric routing or packet reordering using tcpdump: tcpdump -i eth0 'tcp and port 443' -w capture.pcap, then analyze with Wireshark.
  3. 75% success Apply a rate limit on challenge ACKs using iptables to mitigate the storm: iptables -A INPUT -p tcp --dport 443 -m limit --limit 100/s -j ACCEPT 
    Apply a rate limit on challenge ACKs using iptables to mitigate the storm: iptables -A INPUT -p tcp --dport 443 -m limit --limit 100/s -j ACCEPT

中文步骤

  1. Temporarily increase the challenge ACK limit to reduce storm impact: sysctl -w net.ipv4.tcp_challenge_ack_limit=1000
  2. Identify and fix the source of out-of-window segments by checking for asymmetric routing or packet reordering using tcpdump: tcpdump -i eth0 'tcp and port 443' -w capture.pcap, then analyze with Wireshark.
  3. Apply a rate limit on challenge ACKs using iptables to mitigate the storm: iptables -A INPUT -p tcp --dport 443 -m limit --limit 100/s -j ACCEPT

Dead Ends

Common approaches that don't work:

  1. 80% fail

    完全禁用 TCP 挑战 ACK（通过 sysctl net.ipv4.tcp_challenge_ack_limit = 0）会禁用合法安全机制，可能导致盲窗口内攻击。

  2. 90% fail

    重启应用程序或服务器无法解决窗口外段的根本原因，如数据包重排序或非对称路由。

  3. 70% fail

    将挑战 ACK 限制设置过高（例如 net.ipv4.tcp_challenge_ack_limit = 1000000）可能掩盖症状，但无法修复根本原因，并可能延迟网络问题的检测。