Intermediate

DDoS Attack Detection

Build AI systems that accurately distinguish DDoS attacks from legitimate traffic surges, flash crowds, and seasonal peaks.

The Detection Challenge

The hardest part of DDoS defense is distinguishing attack traffic from legitimate surges. A viral marketing campaign, breaking news event, or product launch can cause traffic spikes that look similar to volumetric attacks. AI solves this by analyzing traffic behavior, not just volume.

Detection Features

Feature CategoryExamplesAttack Signal
Volume metricsPPS, BPS, flow countSudden spikes beyond baseline
Source diversityUnique IPs, ASN distribution, geo-spreadMany sources, unusual geographic distribution
Protocol distributionTCP/UDP/ICMP ratios, port distributionAbnormal protocol mix
Packet characteristicsSize distribution, TTL values, flagsUniform packet sizes, consistent TTLs
Behavioral signalsRequest patterns, session behaviorNo follow-up requests, identical patterns
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Key distinction: Legitimate traffic surges show diversity in user agents, request patterns, and browsing behavior. DDoS traffic is often homogeneous - identical request patterns from many sources. AI models learn these behavioral differences.

Detection Approaches

  • Entropy-based: Measure randomness of source IPs, ports, and packet sizes; DDoS often reduces entropy
  • Rate-of-change: Monitor acceleration of traffic metrics, not just absolute values
  • Autoencoder anomaly: Train on normal traffic patterns, high reconstruction error indicates attack
  • Ensemble classification: Multiple models vote on whether traffic is attack or legitimate

Speed Requirements

DDoS detection must be fast to be useful:

  • Volumetric attacks: Detect within 1-5 seconds (before bandwidth saturates)
  • Protocol attacks: Detect within 5-15 seconds (before state tables fill)
  • Application attacks: Detect within 15-60 seconds (before application resources exhaust)
Implementation: Use entropy analysis on 1-second sliding windows for fast volumetric detection, combined with an autoencoder model on 10-second windows for behavioral detection. This dual approach catches both sudden floods and sophisticated application-layer attacks.

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