Intrusion Detection System (IDS) Explained

Table of Contents

An Intrusion Detection System (IDS) is an application monitoring network traffic for detection of potential security threats. When detecting suspicious activities, the IDS issues alerts for the network administrator to investigate and act upon. In this blog post, we will explore the basics of an IDS, from how it works and why it’s important to what its detection methods are and how it differs from other monitoring systems such as the firewall.

What is an IDS?

An Intrusion Detection System (IDS) is a software application monitoring network traffic and searching for known threats and any suspicious activity. The IDS issues alerts to the network administrator when it detects any security risks and threats, which can range from simple policy violations to sophisticated malicious attacks.

Most IDS tools basically monitor and report any unusual or suspicious activity as soon as detected. However, some IDS tools can go beyond that step and take action upon detection of anomalous activity, such as blocking suspicious traffic. This advanced tool is called an IPS or Intrusion Prevention System, and has become the most common implementation option of IDS/IPS technologies.

How does an IDS work?

An IDS works using two basic system and detection types:

Two basic system types

  • NIDS: A NIDS monitors all inbound and outbound traffic from network devices.
  • HIDS: A HIDS monitors an individual network device (or host), scanning inbound and outbound traffic.

Two main detection types

  • Signatures: The IDS system compares an organization’s network activity with an extensive database of publicly known attacks, aiming to find out what’s happening in real time. A signature is a rule that examines a packet or series of packets for certain contents.
  • Anomalies: The system compares current network traffic activity with past activity to identify any major fluctuations, either in the form of sudden increases or decreases in activity, which could be an anomaly worth investigating for security purposes.

Whatever its system or detection types, an IDS remains limited to detecting known attacks, thus could not stop, block, or clean any suspicious traffic.

Why are IDS systems important?

IDSs are important because they can detect malicious or suspicious activity in real time, giving organizations the opportunity to prevent an attack or data breach from occurring in the first place.

For that reason, an IDS is a critical element of a stronger cybersecurity strategy network, adding in an extra layer of protection for the detection of any threats that were able to bypass an organization’s primary layer of defenses.

For instance, a healthcare organization can put in place an IDS to alert the network administrator on a variety of threats that has infiltrated its network, including those that have bypassed its firewalls, thus helping them remain compliant with strict data security regulations.

How does an IDS differ from other monitoring systems?

We’ve already mentioned how an IPS is the most advanced and increasingly preferred option of IDS/IPS technology deployment. But let’s look in more detail at how an IDS differs from some existing network traffic monitoring systems.


  • As a detection system, an IDS typically takes a limited, passive approach to security, monitoring traffic and issuing alerts when malicious or suspicious activity is detected.
  • An IPS, on the other hand, takes a more proactive approach by not only detecting but also blocking or stopping any malicious traffic from entering the network, including malware, phishing, and Denial-of-Service attacks, and also reviewing their source code and policies for any weaknesses.
  • The anomalies detected by an IDS are limited to alerts on what deviates from a baseline of normal activity and require human investigation at the application and protocol levels. Therefore, most IDSs cannot prevent or remediate an organization’s detected threats.

IDS vs. firewall

While both systems are designed to detect and prevent unauthorized access to an organization’s networks and devices, there are some key differences between the two.

  • First, a firewall is deployed at strategic points within an organization’s network – typically at the edge of the network – while an IDS can be deployed across the entire network.
  • Second, a firewall uses predefined rules to allow or block traffic, while an IDS analyzes traffic and looks for anomalies that may indicate malicious activity.
  • Third, a firewall is typically deployed as a hardware appliance, while an IDS can be deployed as either a software application or a hardware appliance.

IDS vs. antivirus

  • An antivirus is a software program that can detect, block, and remove malware from a computer or device. Antiviruses are mostly used to protect individual endpoint devices such as laptops, PCs, and smartphones.
  • An IDS, on the other hand, is a network security tool that monitors traffic for signs of malicious activity. It can be deployed as a hardware, software, or virtual appliance and is mostly used to protect organizations’ networks and infrastructure.
  • While an antivirus is designed to protect individual endpoint devices, an IDS protects an organization’s networks by detecting malicious traffic and issuing alerts so that analysts can investigate and address the threat.

What are some of the best practices in using an IDS?

Some of the best practices in using an IDS can include the following:

  • Keep your threat database current: Once deployed, the IDS should have its threat database continuously updated and done so upon the zero-trust security principle, eliminating implicit trust and continuously validating every stage of a digital interaction.
  • Provide IDS training: Training the IT team members on how to set up the IDS will help them gain a thorough understanding of the device and its role.
  • Set your baseline for normal traffic: To help your IDS detect abnormal or supicious traffic activity, establish a specific initial baseline for normal traffic on your network. By understanding what is “normal” for your organization’s traffic, you can more easily identify anomalies that may indicate malicious activity.
  • Don’t over-tune your IDS: Over-tuning your IDS could increase false positives or negatives. Too many alerts altogether could overwhelm your IT team and expose your organization to a greater risk of cyber attacks.
  • Optimize IDS deployment: To avoid overwhelming your IDS with data, deploy the IDS at the edge of your network, behind the firewall. If you have internal traffic that needs be monitored, deploy multiple IDSs across the network.
  • Configure the IDS for your network: Optimize your IDS default settings for your network devices, applications, ports, protocols, and endpoints, allowing you to set a solid base for effective detection.
  • Enable stealth mode: To make it harder for malicious attackers to detect your IDS, set it up in stealth mode by ensuring the IDS has one interface for the network and another for generating alerts.
  • Test the IDS: To ensure it effectively detects potential threats, regularly submit your IDS to a professional penetration test. This will also allow you to find and fix any potential vulnerabilities in your network before they are exploited by malicious attackers.

What are the key benefits of an IDS?

Among the benefits of deploying an IDS over your network are the following:

  • A clearer picture of your threat landscape: An IDS tool can help you get a clearer picture of the actual types, sophistication levels, and volumes of cyber attacks targeting your systems. Understanding your organization’s threat landscape can also help better fine-tune your IDS deployment and incident response plan.
  • A more effective, fact-driven security strategy: Getting a better grasp of your threat landscape will help you devise and continuously improve the an effective cybersecurity strategy. An IDS will also help you identify bugs and potential flaws in your devices and networks, thus assessing and adapting their defenses to any emerging risks.
  • Increased regulatory compliance readiness: The data your IDS gathers will prove very handy to keep up with a growing list of increasingly stringent security regulations to comply with, thus easing your regulatory process.
  • Faster threat inspection and response times: The IDS immediate, real-time alerts allow you to detect and prevent attacks while inspecting data in packets and operating systems faster than through manual monitoring.

Final thoughts

An Intrusion Detection System (IDS) can be a powerful ally in the fight against cybercrime. By helping you understand your threat landscape and devise an effective cybersecurity strategy, it can help you prevent attacks, while also providing data that will prove useful to meet compliance regulations. When used correctly, an IDS can be a key component of a strong cybersecurity posture. However, an IDS is no silver bullet, and should ideally be deployed as the more proactive-driven IPS/IDS option, along with the right arsenal for your overall strategy.

Contact us if you need help with your enterprise security.

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