IDS vs. IPS: Key Differences Explained

What is an IDS?

An intrusion detection system (IDS) is designed to monitor network traffic and detect suspicious activity or potential security threats. It works by analyzing inbound and outbound traffic against known attack signatures or patterns. It identifies irregularities or threats, such as a malware attempt or unauthorized access, alerting administrators to take action. A key characteristic of an IDS is that it is a passive system. It detects and alerts but does not intervene in the traffic itself. This makes it suitable for environments where passive monitoring is preferred. After receiving an alert from an IDS, a user must manually take action to investigate the root cause and remedy it.

Types of IDS

The four main types of IDS are as follows:

• Network Intrusion Detection System (NIDS): Monitors network traffic through sensors placed throughout the network. A NIDS monitors the entire enterprise network and tracks traffic to and from every device, using metadata and packet content to make decisions. NIDS has a wider view than HIDS, providing more context for detecting widespread threats, but might lack granular visibility into specific devices.
• Host Intrusion Detection System (HIDS): Monitors traffic on the specific device or system where it is installed. A HIDS is deployed at the endpoint level to protect individual devices, monitoring traffic flowing in and out, tracking running processes, and examining system logs. HIDS protects only its host machine and thus lacks access to complete network data for broader context, but it offers granular visibility into the host's workings.
• Protocol-based Intrusion Detection System (PIDS): Placed between a device and a server to monitor all traffic flowing between them. This type is leveraged to secure users browsing the internet.
• Application Protocol-based Intrusion Detection System (APIDS): Placed within a group of servers to watch how they communicate with one another, often leveraged on specific application protocols.

A hybrid IDS combines some of the above approaches.

IDS solutions use two primary methods for threat detection: signature-based and anomaly-based. Signature-based detection uses a list of known attack behaviors (signatures) to identify attacks that match or resemble those patterns.

Anomaly-based detection establishes a baseline model of normal behavior and flags any activity that deviates from this baseline as potentially suspicious. Many vendors use AI and machine learning to improve anomaly detection capabilities.

What is an IPS?

An intrusion prevention system (IPS), sometimes referred to as an intrusion detection prevention system (IDPS), not only detects malicious activity but also actively prevents or blocks potential threats in real-time. IPS works similarly to IDS by analyzing network traffic, but it takes immediate action.

This proactive approach helps prevent attacks before they can cause damage. An IPS is generally placed in the direct path of network traffic, often behind the firewall. This inline positioning allows it to scrutinize and act on threats in real time.

Common automated responses by an IPS include:

• Blocking the traffic source address
• Dropping malicious packets
• Severing malicious connections
• Sending alerts to the user
• Closing sessions
• Strengthening firewalls
• Cleaning up malicious content

Fundamentally, an IPS is not just a diagnostic tool but a solution that can respond to detected network security threats.

Types of IPS

There are four main types of IPS:

• Network-based IPS (NIPS): Analyzes and protects traffic on the entire network.
• Wireless IPS (WIPS): Observes activity within a wireless network and defends against attacks launched from there, often monitoring for rogue access points.
• Network Behavior Analysis (NBA): Spots attacks involving unusual traffic patterns on the network, such as DDoS attacks or policy violations.
• Host-based IPS (HIPS): Scans events occurring within a specified host.

Like IDS, IPS uses signature-based and anomaly-based detection methods. Signature-based IPS scans for patterns indicating vulnerabilities or exploitation attempts by comparing network activity against known threat signatures.

Anomaly-based IPS analyzes network traffic against a baseline model of normal behavior to identify performance anomalies and trigger automated responses. Cutting-edge IPS solutions incorporate AI and machine learning to enhance anomaly detection and reduce false positives.

Policy-based IPS relies on security policies set by the organization to detect and block violations.

How IDS and IPS differ

The fundamental difference between IDS and IDP lies in their response to detected threats.

• IDS is passive: It monitors and generates alerts but does not take action to stop the traffic or prevent the intrusion. Human intervention by security teams is required to address the threat after an alert is received.
• IPS is active: It not only detects but also actively prevents threats in real time by taking automated actions like blocking traffic or dropping network packets. An IPS can identify and block the attack automatically.

This core difference leads to other distinctions:

• Level of Protection: IPS offers more protection because it acts automatically to contain the threat, leaving less time for an attacker to compromise the organization further. With IDS, the user has to remediate the incident manually after an alert.
• Placement in the Network: IDS is typically positioned out of band, meaning it monitors a copy of the network traffic without being directly in the traffic path. This nondisruptive placement preserves network performance. IPS is placed inline, directly in the path of network traffic (often behind the firewall), allowing it to intercept and act on threats before they reach their target.
• Impact on Network Operations: Because IPS is inline and actively blocks traffic, it has the potential to impact network performance, such as introducing latency or blocking legitimate traffic (false positives) if not properly configured. IDS, being passive and out-of-band, has minimal-to-no impact on network performance.
• Scope and Function: IDS is primarily a monitoring and diagnostic tool focused on detection and alerting. IPS is a control-based solution that performs detection and then enforces rules to allow or deny traffic. An IPS can perform the functions of an IDS, but an IDS cannot perform the prevention functions of an IPS.

Key similarities between IDS and IPS

Despite their differences, IDS and IPS share significant similarities:

• Shared Purpose: Both are essential network security components designed to protect enterprise networks from threats and unauthorized access. They aim to identify cyberattacks that can damage a company's information assets.
• Threat Detection Methods: Both utilize similar methods for detecting threats, primarily signature-based and anomaly-based detection. They compare network traffic against databases of known attack signatures or models of normal network behavior. Some solutions may combine both approaches (hybrid methodology).
• Monitoring and Analysis: Both systems monitor network traffic and activity across devices and servers in real time.
• Alerting Capabilities: Both systems are capable of generating alerts or notifications when potential threats or suspicious activities are detected.
• Learning and Logging: Depending on their detection methods (especially anomaly-based), both can use machine learning to understand patterns and emerging threats. Both keep records or logs of monitored activity and detected events, which can be used for analysis, reporting, and forensic investigations.
• Policy Management: Both can be managed and configured through policies defined by network administrators. Policy-based detection is also a method used by some IPS solutions.
• Relevance for Modern Enterprises: With increasing access points, data volumes, and sophisticated threats, both cutting-edge IDS and IPS are considered vital parts of the cybersecurity systems of modern organizations, enabling swift and efficient responses. They leverage automation to protect digital environments.
• Compliance and Policy Enforcement: Both can help organizations meet compliance requirements by providing industry-standard data protection measures and maintaining auditing records. They can also be set up to enforce security policies at the enterprise network level.

IDS and IPS: better together

Many modern security systems and organizations find that deploying both IDS and IPS is the best approach to achieve a comprehensive security solution. This layered approach ensures that even if a threat bypasses the initial filter (like a firewall), the IDS can detect it and the IPS can take action to prevent harm.

The term “intrusion detection and prevention system” (IDPS) is often used to describe a solution that combines the functionalities of both IDS and IPS. When people use "intrusion prevention system" (IPS), the "detection" action is often implied, essentially making IDPS and IPS terms mostly interchangeable in some contexts. However, it's also common for organizations to view IDS and IPS as separate but mutually reinforcing functions.

In a combined IDS and intrusion prevention setup, the IPS provides active network security by blocking threats, while the IDS can offer deeper insights into network traffic patterns. This combination allows for strong prevention and monitoring, which is considered the most effective strategy in today's threat landscape.

While IDS and IPS are critical, they are not standalone solutions that will take care of cybersecurity by themselves. Proper configuration and continuous management by trained employees are crucial for their effectiveness. They must be integrated carefully into the monitoring environment to avoid issues like false positives.

Other security technologies, such as next-generation firewalls (NGFW), unified threat management (UTM) devices, network detection and response (NDR), and security information and event management (SIEM) solutions, often incorporate or work in conjunction with IDS/IPS capabilities.

Excel with Trellix Intrusion Detection and Prevention

Trellix Intrusion Prevention System is a next-generation intrusion detection and prevention system (IDPS) that uses advanced detection and emulation techniques, moving beyond traditional pattern matching to defend against stealthy attacks with a high degree of accuracy.

Trellix IPS combines signature-based detection with advanced botnet and malware detection, advanced intrusion prevention, DOS and DOS prevention, and sandboxing. This multilayered approach enables Trellix IPS to detect and block known and unknown threats, including zero day exploits and sophisticated malware. The system also offers high performance, scalability, and seamless integration with cloud environments, making it suitable for modern, hybrid network architectures.