What is an intrusion detection system and how does it work?

What is an intrusion detection system?

An intrusion detection system (IDS) is an important part of enterprise-level network security technology. IDS software helps detect vulnerabilities in the network that attackers could exploit against a company’s devices and systems. However, while an IDS is excellent at identifying potential threats and issuing alerts, it lacks the ability to actively block or prevent those threats from causing harm. This is where an intrusion prevention system (IPS) can be useful.

But while an IPS can detect suspicious activity and take pre-configured measures to mitigate threats, you shouldn’t think about your security infrastructure in terms of IDS vs IPS. Effective cyber threat monitoring and prevention depends on having both of these tools — as well as reliable antivirus software and a VPN.

How does an intrusion detection system work?

In simple terms, an IDS is like a vigilant guard who continually monitors the network for any signs of suspicious activity or outright cyber attacks. Two primary methods an IDS uses to detect possible intrusion are signature-based detection and anomaly-based detection.

Signature-based detection is like Tinder. Just like you’re likely to have some criteria you’re looking for when browsing the app, IDS uses a database of known attack patterns, also known as "signatures." When the IDS scans network traffic, it compares every data packet to attack patterns in its database as well as can perform deep packet inspection. If it finds a match, such as a known signature for phishing or malware, it raises an alert.

Anomaly-based detection is a little more interesting because instead of just looking for known attack signatures, the software must learn what “normal" behavior looks like for the network. For example, it establishes a baseline based on regular network traffic patterns and scans the network for anything that deviates from this baseline. While anomaly-based detection systems can help uncover unknown threats, they can also result in more false positives.

Intrusion detection system types

While there are several types of intrusion detection systems, the two most common are network-based and host-based intrusion detection systems. The former looks after the entire network, while the latter protects one device.

NIDS (network intrusion detection system)

NIDS is designed to monitor and analyze incoming and outgoing network traffic and look for threats or suspicious activity. While it scans all traffic and checks the contents of its data packet and metadata, NIDS cannot provide full coverage within the network. That’s why NIDS should be implemented strategically, to cover devices and ports that are most likely to be attacked.

HIDS (host-based intrusion detection system)

A host-based IDS is designed to protect the device, or the host, it is installed on. It can analyze inbound and outbound traffic, check for signs of malicious intent, and even notify the authorities.

PIDS (protocol-based intrusion detection system)

A protocol-based intrusion detection system scrutinizes the network protocols used in your infrastructure for irregularities and signs of malicious activity. It works by comparing network traffic against predefined protocol behavior such as the structure and sequence of packets. PIDS is extremely effective at detecting attacks that exploit vulnerabilities in network protocols but requires a thorough understanding of each protocol’s normal behavior.

APIDS (application protocol-based intrusion detection system)

An application protocol-based IDS focuses on communication at the application protocol layer. It understands the expected behavior of software and is designed to identify unusual actions that could signify an attack. While APIDS can be resource-intensive due to the depth of its monitoring, it is adept at detecting attacks that other systems might miss.

Hybrid IDS (hybrid intrusion detection system)

As the name suggests, a hybrid IDS is a combination of two or more types of intrusion detection systems, bringing together the strengths of HIDS and NIDS. It can perform data packet inspection (like NIDS) and system behavior analysis (like hybrid IDS), offering a comprehensive defense against a wide range of threats. This approach provides broader visibility and more robust protection, but it may also require more resources and careful configuration to reduce false positives.

What is the difference between IDS and firewalls?

IDS solutions and firewalls both help protect a network but there are subtle differences in how each does its job.

All types of intrusion detection systems passively monitor traffic, keeping an eye out for anything suspicious. If it finds anything, an IDS is ready to react —- send an alert to the network administrator.

A firewall is more like a bouncer for your network, you can give a list of names or criteria on who and what you want to be let inside. In other words, a firewall is like a barrier between your network and outside threats. However, an IDS is a passive tool, scanning the network but not interfering with files or data packets, while a firewall can actively block files and prevent malicious traffic from reaching your network.

Why are intrusion detection systems important?

As cyberattacks continue to grow in complexity and sophistication, businesses must ensure that they maintain high levels of security to safeguard against emerging threats. Intrusion detection systems help protect your company network and devices, while various types of IDS solutions provide the flexibility needed to adapt them to individual security needs.

The primary benefit of an IDS is that it serves as an early warning solution, alerting the network administrators whenever their network activity deviates from the norm. But an IDS can also help organizations with compliance and improving their security posture. In simple terms, IDS is one of the key aspects of network security standards.

Lastly, it’s a great tool to add to your security arsenal along with anti-malware software, intrusion prevention systems, and other tools that can help identify or prevent malicious activity.