What is Intrusion Detection System

What is Intrusion Detection System

With the ever-increasing sophistication of cyber threats, it has become crucial for organizations to deploy robust security measures to safeguard their systems. One such essential tool in the field of cybersecurity is an intrusion detection system (IDS). In this article, we will explore what an intrusion detection system is, its types, detection techniques, deployment strategies, challenges, best practices, and more.


An intrusion detection system (IDS) is a security technology that helps identify and respond to malicious activities or policy violations in a computer network or on individual hosts. Its primary objective is to detect and alert security personnel about potential threats or attacks that could compromise the confidentiality, integrity, or availability of data and systems. By analyzing network traffic or host activities, an IDS acts as a vigilant guardian, monitoring for suspicious patterns and deviations from normal behavior.

Types of Intrusion Detection Systems

There are two main types of intrusion detection systems: network-based IDS (NIDS) and host-based IDS (HIDS).

Network-based IDS (NIDS)

A network-based IDS (NIDS) operates at the network level, monitoring and analyzing network traffic for potential security breaches. It uses sensors strategically placed throughout the network to capture packets and analyze their contents. NIDS can detect a wide range of network-based attacks, such as port scanning, denial-of-service (DoS) attacks, and intrusion attempts.

However, NIDS has its limitations. It may struggle to detect attacks that use encrypted traffic or those that exploit vulnerabilities at the application layer. Additionally, NIDS can generate a high volume of alerts, leading to a phenomenon known as “alert fatigue,” where legitimate alerts can be overlooked amidst the noise.

Host-based IDS (HIDS)

In contrast to NIDS, a host-based IDS (HIDS) operates at the individual host level. It monitors the activities and events occurring on a specific device, such as a server or workstation, to identify potential security breaches. HIDS collects data from various system logs, including file integrity, system calls, and user activities, to detect suspicious behavior or unauthorized access attempts.

HIDS provides a more granular view of host activities and can detect attacks that may go unnoticed by NIDS, such as insider threats or attacks targeting specific vulnerabilities on a host. It offers enhanced visibility into the security posture of individual devices and allows for immediate response and containment actions.

However, HIDS also has limitations. It relies on the host’s resources for monitoring, which may impact system performance. Additionally, HIDS is less effective against network-level attacks that do not directly target the host being monitored.

Detection Techniques Used by IDS

Intrusion detection systems employ various techniques to identify and differentiate between normal and malicious activities. Let’s explore the three primary detection techniques used by IDS.

Signature-based detection

Signature-based detection, also known as rule-based detection, involves comparing observed data or network traffic against a database of known attack signatures or patterns. These signatures are created based on the characteristics and behaviors of previously identified attacks.

When an IDS encounters a match between observed data and a known signature, it generates an alert. Signature-based detection is effective in identifying well-known and documented attacks. However, it relies on regular updates of signature databases to keep up with new and emerging threats.

Anomaly-based detection

Anomaly-based detection focuses on identifying deviations from normal behavior or patterns. It establishes a baseline of normal activities by monitoring and analyzing network traffic or host behaviors over a period of time. Any activity that significantly deviates from the established baseline is flagged as suspicious and triggers an alert.

Anomaly-based detection can identify previously unseen or zero-day attacks since it does not rely on known signatures. It is particularly useful in detecting attacks that exhibit unusual or uncommon behavior. However, this technique may generate false positives if legitimate activities are not properly accounted for in the baseline.

Behavior-based detection

Behavior-based detection is similar to anomaly-based detection but focuses on specific behaviors associated with different types of attacks. It leverages machine learning algorithms to analyze patterns and behaviors in network traffic or host activities and identify deviations that may indicate an ongoing attack.

Behavior-based detection can adapt and learn from new attack patterns, making it effective against evolving threats. By monitoring for specific behaviors typically associated with attacks, it can provide more accurate alerts with reduced false positives. However, it may require significant computational resources for training and analysis.

Deployment Strategies for IDS

Intrusion detection systems can be deployed in different ways to effectively monitor and protect networks and hosts. Let’s explore two common deployment strategies: network intrusion detection systems and host intrusion detection systems.

Network intrusion detection systems

Network intrusion detection systems are placed strategically within the network infrastructure to monitor and analyze network traffic. They are typically positioned at key network entry and exit points, such as firewalls or routers, to capture and inspect all incoming and outgoing packets.

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