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Intrusion Detection System (IDS)

An Intrusion Detection System (IDS) is a monitoring tool that analyzes network or host activity to identify suspicious behavior and alert security teams to potential attacks.

What is IDS?How it typically works?Common techniquesImpactFurther reading

What is IDS?

An IDS provides visibility into what is happening across systems and networks by comparing observed activity against known attack signatures or expected behavior. Unlike a firewall, which blocks traffic, an IDS is a passive system designed to detect and alert. For SecOps teams, IDS is a first line of defense that surfaces unusual events, enabling analysts to investigate before damage occurs.

How it typically works?

  1. Traffic capture: IDS collects packets from a network or logs from a host.
  2. Analysis: signatures or anomaly detection algorithms are applied.
  3. Alerting: suspicious activity triggers an alert in the SOC.
  4. Investigation: analysts review alerts to determine if an incident is real or a false positive.

Common techniques

  • Network IDS (NIDS): monitors traffic across network segments.
  • Host IDS (HIDS): monitors system activity, logs, and integrity of files.
  • Signature-based detection: matches known attack patterns such as Snort rules.
  • Anomaly-based detection: uses baselines of normal traffic to spot deviations.
  • Hybrid IDS: combines signatures and anomalies for better coverage.
  • Open-source IDS: Suricata and Snort are widely used in enterprise environments.

Impact

IDS helps detect intrusions early but does not block them. Its value lies in visibility, forensic data, and support for compliance. However, IDS systems are prone to false positives and require tuning. For SecOps, IDS is best used as part of a layered defense strategy, providing context that complements firewalls, IPS, and SIEM.

Further reading

Related topics

Intrusion Prevention System (IPS)SIEMThreat Intelligence