What Is an Intrusion Detection System?

Key Takeaways

• An intrusion detection system (IDS) is an application or device that monitors and analyzes a network against malicious threats.

• An IDS does not offer protection for endpoints or networks beyond incident response, it passively observes and alerts incident responders or SOC analysts to potential threats.

• You can explore how an IDS supports cybersecurity strategies in the following article.

Continue reading to learn how intrusion detection systems work, how they differ from firewalls, and which types may apply to your organization's security needs. If you're interested in sharpening your skills in this area to enhance your resume, consider enrolling in John Hopkins' University's Intrusion Detection Specialization. In as little as four months, you'll master in-demand skills like machine learning techniques to improve threat detection and incident response strategies.

What is an intrusion detection system?

An IDS is a application or device that screens, monitors, and analyzes a network for malicious threats. Unlike a firewall, which actively blocks traffic, an IDS passively observes network activity and alerts incident responders or SOC analysts to potential threats. IDS solutions come in two primary forms: a network intrusion detection system (NIDS), which monitors traffic across an organization's internal network, and a host-based intrusion detection system (HIDS), which safeguards individual devices and catches threats that NIDS may miss.

HIDS vs NIDS intrusion detection systems

IDS solutions come in different forms, each with its own capabilities tailored to meet specific security requirements. Here are two prevalent types of intrusion detection systems:

• NIDS: Network intrusion detection systems are strategically placed within an organization's internal network infrastructure to actively monitor and identify any malicious or suspicious traffic originating from devices connected to the network.

• HIDS: A host intrusion detection system (HIDS) safeguards all devices that connect to both the internet and the organization's internal network. It detects internal packets and additional malicious traffic missed by NIDS. HIDS also identifies host-based threats, like malware attempting to spread within an organization's system.

Examples of intrusion detection systems

Your IDS may have complex technical and surprisingly simple components. Intrusion detection system examples include motion sensors, glass break sensors, alarms, video surveillance, thermal cameras, and security software like Cisco Secure Firewall or Trellix Network Security.

How do intrusion detection systems work?

An IDS supports organizations in their cybersecurity strategies by offering assistance in one of three ways:

• Signature-based detection: The IDS examines all packets traversing an organization's network and matches them against a database of known attack signatures through string comparison.

• Anomaly-based detection: The IDS compares definitions of what is deemed normal with recorded events to spot deviations in network activity. Anomaly-based systems employ machine learning to establish a reference point for normal behavior. This detection method can prove instrumental in combating novel threats. 

• Stateful protocol analysis: The IDS analyzes observed events with predefined profiles of protocol activity that are safe or benign. The process repeats for every protocol state.

IDS vs. firewall: What’s the difference? 

An IDS passively observes network activity, alerting incident responders or security operations center (SOC) analysts to potential threats. However, it does not offer protection for endpoints or networks beyond incident response.

In contrast, a firewall actively monitors and blocks threats to prevent incidents. It acts as a barrier, selectively allowing or blocking network traffic based on preconfigured rules.

Related terms

• CIA triad

• Computer forensic investigator

• Cybersecurity analyst

• Security engineer

• Information security analyst

• Cryptanalyst

Learn more about IDS with Coursera's free resources

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