What is an intrusion detection system (IDS)?

What are Intrusion Detection Systems and Intrusion Detection Systems? Are the terms IDS and IPS interchangeable? Both intrusion protection and intrusion detection systems are forms of network security that protect against cyber threats. They often work together, but they are different.

IDS and IPS are essential components of a comprehensive cybersecurity strategy, helping organizations protect their assets and sensitive data from various cyber threats. Read on to learn more about each, how they differ, and how they can work together to protect you from cyber threats.

About Intrusion Prevention System (IPS)?

An intrusion prevention system (IPS) is an active security system that detects potential threats and takes automated actions to prevent or block them in real-time. IPS uses the same techniques as IDS, such as signature-based detection, anomaly detection, and heuristics, to identify threats. When an IPS identifies a malicious or unauthorized activity, it can take predefined actions to block the offending traffic or connection, effectively stopping the intrusion attempt.

How Does an IPS Work?

Intrusion Prevention Systems monitor network traffic in real time, analyze the data packets, and compare them against known attack patterns or signatures. Here's how IPS generally works:

• Traffic Monitoring: IPS continuously monitors incoming and outgoing network traffic, examining data packets as they traverse the network.
• Packet Inspection: It performs deep packet inspection, which involves examining the content of each data packet, including the header and payload. This thorough inspection allows the IPS to analyze the behavior and characteristics of the traffic.
• Signature-Based Detection: One of the primary methods an IPS uses is signature-based detection. It compares the characteristics of the data packets to a database of known attack signatures associated with malware, viruses, or other malicious activities. If a match is found, the IPS can block or log the malicious traffic.
• Anomaly-Based Detection: Some IPS employ anomaly-based detection. They establish a baseline of what is considered normal network behavior. If the IPS detects traffic that deviates significantly from this baseline, it may flag it as suspicious. This approach is helpful in detecting previously unknown or zero-day attacks.
• Traffic Blocking: When the IPS identifies potentially malicious traffic based on its analysis, it can take various actions to protect the network. These actions may include blocking malicious traffic, dropping packets, or rerouting traffic to a quarantine area for further analysis.
• Alerting and Reporting: The IPS usually generates alerts to notify network administrators of detected threats or suspicious activities. These alerts provide information about the threat's nature, the traffic's source and destination, and the action taken by the IPS. Network administrators can then investigate and respond to the alerts.
• Customization and Tuning: IPS systems can be customized and tuned to suit an organization's specific needs. This may involve creating custom signatures, adjusting sensitivity levels, and configuring response actions.
• Integration with Other Security Tools: IPS often works in conjunction with other security technologies to provide layered security defenses.
• Continuous Updates: To effectively protect against new and evolving threats, IPS databases of attack signatures and anomaly detection models need to be regularly updated. These updates ensure that the IPS can recognize the latest threats.

What is an Intrusion Detection System (IDS)?

An IDS is a passive security system that monitors network traffic or system activities to identify potential security incidents, policy violations, or abnormal behavior. IDS analyzes network packets, logs, or system events to detect known attack patterns, vulnerabilities, or deviations from established baselines.

IDSs are classified into two main types:

• Network-based IDS (NIDS): Monitors network traffic and looks for patterns or signatures of known attacks or suspicious activity. It can be deployed at various points within a network.
• Host-based IDS (HIDS): Monitors activities on individual hosts or devices, such as servers or workstations. It focuses on identifying suspicious activities occurring on the host itself.

 When an IDS detects suspicious activity or potential threats, it generates alerts or notifications, which security personnel can review and investigate.

How Does an IDS Work?

An Intrusion Detection System (IDS) works by monitoring network traffic or system activity for signs of malicious or unauthorized activities. It identifies and alerts administrators to potential security breaches.

There are two main types of IDS: Network-based Intrusion Detection Systems (NIDS) and Host-based Intrusion Detection Systems (HIDS).

Network-based Intrusion Detection Systems (NIDS):

• Packet Capture: NIDS monitors network traffic by capturing and analyzing packets as they pass through a network interface. It inspects traffic at the network layer (Layer 3) and above.
• Signature-Based Detection: This is the most common method used by NIDS. It compares network traffic against a database of known attack patterns or signatures. When it detects a match, it generates an alert.
• Anomaly-Based Detection: Some NIDS use anomaly detection techniques in addition to signature-based detection. They establish a baseline of normal network behavior and then flag any deviations from this baseline as potential intrusions. Anomaly detection can help detect previously unknown threats.
• Heuristic-Based Detection: This method uses rules and heuristics to identify suspicious patterns of network behavior. It is more flexible than signature-based detection but may generate more false positives.
• Alerting and Reporting: When the NIDS identifies suspicious or malicious activity, it generates alerts for network administrators. These alerts can include information about the detected threat, its severity, and recommendations for remediation.

Host-based Intrusion Detection Systems (HIDS):

• Agent-Based Monitoring: HIDS is installed on individual hosts (servers or endpoints) and monitors system activities on those hosts.
• File Integrity Monitoring: HIDS checks the system and configuration files' integrity. Any unauthorized changes or modifications trigger alerts.
• System Logs Analysis: HIDS analyzes system logs, looking for patterns or events that indicate unauthorized access or unusual activity on the host.
• Behavioral Analysis: Similar to anomaly-based detection in NIDS, HIDS can monitor the behavior of processes and applications on a host to detect deviations from the expected behavior.
• Alerting and Reporting: Just like NIDS, HIDS generates alerts when it detects suspicious activity on a host. Administrators receive these for further investigation.

The key to effective IDS operation is tuning and configuration. Administrators must define which activities or behaviors are considered suspicious or malicious and set up the alerting system accordingly. IDSs are often used with Intrusion Prevention Systems (IPS), which not only detect but can also take automated actions to block or mitigate detected threats.

What’s the difference between IPS and IDS?

As mentioned above, IPS is an active cybersecurity measure, while IDS is passive security. IDS primarily focuses on detection and alerting, while IPS goes further by actively preventing or mitigating threats.  

IPS and IDS are security systems used to protect computer networks from various threats, but they serve different purposes and operate slightly differently. Here are the key differences between IPS and IDS.

• Active vs. Passive Security: The primary purpose of an IPS is to actively block or prevent malicious activity and network intrusions in real time. It monitors network traffic for suspicious or unauthorized activity and immediately blocks or prevents it, such as dropping packets, closing connections, or reconfiguring network rules. An IDS, on the other hand, is designed to detect and alert on suspicious or potentially harmful network activity but does not take any active measures to prevent or block the detected activity. It provides alerts or logs that are analyzed by security personnel, who then take appropriate action based on the alerts.
• Blocking and Prevention vs. Observation and Analysis: IPS actively takes action to prevent or block malicious activity. This can include blocking network traffic, modifying firewall rules, or resetting connections to protect the network from threats. Meanwhile, IDS passively observes and analyzes network traffic, generating alerts when it detects suspicious or potentially harmful activity. Security analysts or administrators must review these alerts and decide on the appropriate action.
• False Positive Rates: Because an IPS actively blocks traffic based on its analysis, it may have a higher likelihood of generating false positives, potentially blocking legitimate traffic if misconfigured or if the detection rules are too strict. Conversely, IDS systems tend to have fewer false positives since they do not actively block traffic. However, they may generate more alerts that need to be reviewed by human operators.
• Network Performance Impact: The active blocking nature of an IPS can have a direct impact on network performance, and it may introduce latency if it is processing a large volume of traffic or if it's incorrectly configured to block legitimate traffic. IDS, being a passive monitoring system, has a lower impact on network performance since it does not interfere with network traffic.
• Deployment: IPS is typically placed in-line with network traffic, meaning that all traffic passes through it, allowing it to actively block threats. It's considered a security gateway.

However, IDS can be deployed in various ways, including in-line (similar to IPS), out-of-band (where it monitors a copy of network traffic), or as a host-based IDS on individual devices.

What Are the Benefits of Deploying IDS and IPS?

Intrusion Detection Systems (IDS) and Intrusion Prevention Systems (IPS) offer a range of benefits to enhance the security of a network, including:

• Threat Detection: IDS monitors network traffic and system activities in real time, looking for suspicious patterns or behaviors. An IDS detects various types of threats, such as malware, unauthorized access attempts, and unusual traffic patterns.
• Early Warning: IDS provides early warning of potential security incidents, allowing organizations to take proactive measures to mitigate threats before they escalate into full-blown attacks.
• Incident Investigation: IDS logs and stores data related to detected threats, which is valuable for forensic analysis. This information helps security teams understand the nature of the attack, its origin, and its potential impact.
• Compliance and Reporting: Many regulatory frameworks and industry standards require organizations to have IDS in place to monitor and report on security events. Deploying IDS can help organizations meet compliance requirements.
• Reduced Downtime: By detecting and addressing threats early, IDS can help reduce downtime and minimize the impact of security incidents on business operations.

Benefits of Deploying IPS:

• Real-time Threat Mitigation: IPS goes a step further than IDS by actively blocking or mitigating detected threats in real-time. It can drop malicious packets, block access to malicious websites, or trigger other security measures to prevent attacks.
• Automated Response: IPS can automatically take action to protect the network and systems, reducing the need for manual intervention. This is especially important in the case of fast-spreading or automated attacks.
• Improved Security Posture: IPS helps maintain a proactive and robust security posture by preventing known and emerging threats from compromising the network or systems.
• Reduced Attack Surface: By actively blocking malicious traffic, IPS reduces the attack surface and minimizes the potential impact of security breaches.
• Enhanced Network Performance: While there may be some overhead associated with IPS, it can help optimize network performance by preventing resource-intensive attacks and ensuring that legitimate traffic flows smoothly.
• Compliance Adherence: Just like IDS, IPS can assist organizations in meeting regulatory compliance requirements by actively protecting against security threats.
• Zero-Day Threat Prevention: Some advanced IPS solutions are capable of detecting and preventing zero-day attacks or previously unknown threats through advanced threat intelligence and behavioral analysis.

Sophos on IDS and IPS

It's important to note that IDS and IPS are not standalone solutions but part of a layered security strategy. Together with firewalls, next-gen antivirus software, and other security measures, they contribute to a comprehensive security posture that helps protect organizations against a wide range of threats. Additionally, they should be configured and monitored by skilled security professionals to maximize their effectiveness while minimizing false positives.

For many organizations, the best way to manage all of these components is to opt for a Next Generation Firewall (NGFW) Solution or Managed Detection and Response with a cybersecurity provider.

Learn More about MDR

Related security topic: What are indicators of compromise?