An intrusion detection system (IDS) monitors network traffic or host activity for signs of attacks and policy violations and raises alerts for security teams.
How an IDS works
There are two main deployment types:
- Network IDS (NIDS) analyses copies of traffic from a switch port or network tap. Well-known open-source examples are Snort (released in 1998), Suricata and Zeek.
- Host IDS (HIDS) runs on servers and workstations and watches logs, file integrity and system calls – for example OSSEC or Wazuh.
Detection methods include signatures – rules describing known exploits, malware traffic and indicators of compromise – and anomaly detection, which learns normal behaviour and flags deviations. Signatures are precise but miss new attacks; anomaly detection finds unknown threats but produces more false positives.
IDS vs. IPS
An IDS only observes and alerts. An intrusion prevention system (IPS) sits inline and can block malicious traffic automatically. Many products, including next-generation firewalls, combine both functions and let administrators choose detect or block mode per rule.
Why IDS matters
An IDS gives visibility into what crosses the network: exploitation attempts against servers, command-and-control traffic, lateral movement and data exfiltration. Alerts are usually sent to a SIEM and analysed by the SOC. Network detection remains valuable even with endpoint protection, because many devices – printers, IoT, appliances – cannot run security agents.
Best practices
- Place sensors at the perimeter and at key internal segments, not only at the internet edge.
- Keep rule sets updated and tune them to reduce noise.
- Decrypt or inspect TLS where allowed, since most traffic is encrypted.
- Correlate IDS alerts with endpoint and log data.
