IDS vs IPS: The Definitive Comparison

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IDS vs IPS: the definitive comparison!

Intrusion Detection Systems (IDS) and Intrusion Prevention Systems (IPS) are two of the most widely used tools in modern cybersecurity environments. Even some of the best next-generation firewalls (NGFWs) incorporate them! Often, people believe that IDS and IPS are inseparable. But the truth is, they’re two different systems. This IDS vs IPS article will clarify their differences. This way, you’ll know which to use for your business.

First, I’ll show you a clear comparison between them. I’ll also explain which system you should deploy. But why is it important to know the differences between IDS vs IPS? Let’s find out. 

Why You Need to Differentiate IDS vs IPS

Google Trends has shown a constant interest in the term “difference between ids and ips” over the past 5 years. Some of these search queries came from IT students. But who else is researching about IDS vs IPS? I can think of 3 categories:

  1. People in the business sector
  2. IT employees in small businesses
  3. Not-so-technical decision makers in large enterprises 
Chart of the interest over time in the search term "difference between ids and ips". The chart shows the interest has remained strong for the past 5 years.
Google Trends show people are searching for IDS vs IPS comparisons.

Because IDS and IPS are cybersecurity solutions, it’s apparent that businesses of all sizes are becoming more concerned with cybersecurity. And in their search for a solution, they stumbled on the unresolved IDS vs IPS debate. 

IDS and IPS solutions can cost up to tens of thousands of dollars. This means an erroneous purchase can hurt your bottom line. You need to differentiate between IDS vs IPS to make the right purchase for your business. So let’s get to know both systems, starting with IDS. 

What Is an Intrusion Detection System (IDS)?

An intrusion detection system (IDS) is an appliance or software application. It detects an intrusion and sends out corresponding alerts. The alerts may go to log files, a SIEM, or another security tool. These all help ingest telemetry data from other sources. Finally, a trained threat analyst interprets the IDS’ generated log data

A complete IDS deployment may have multiple sensors or agents, management servers, consoles, and databases. IDS solutions are also modular. This means you can deploy components separately. But for the sake of brevity, I’ll treat these as one entity—an IDS. That way, we can focus our discussion on the salient points to help us make a clear IDS vs IPS comparison. 

That said, let’s move on to the second part of our discussion, the IPS.

What Is an Intrusion Prevention System (IPS)?

Like an IDS, an Intrusion Prevention System (IPS) also detects potential threats and sends alerts. Unlike an IDS, which only detects an intrusion while it’s underway, an IPS can actually prevent the intrusion. An IPS automatically blocks threats before they enter the network or host behind it.  

A complete IPS deployment may have multiple sensors or agents, management servers, consoles, and databases. IPS solutions are also modular. This means you can deploy their components separately. And just like I did with IDS, I’ll treat these components as one entity—an IPS.  

But at first glance, it doesn’t look like IDS and IPS are that different. So let’s dive deeper into their similarities and differences. 

IDS vs IPS​​Similarities and Differences

We discussed the main qualities of an IDS and IPS earlier. Let’s compare and contrast the two based on the information we know. To start, IDS and IPS share some similarities. For instance, they both use the same intrusion detection methods, like: 

  • Pattern or signature-based intrusion detection
  • Anomaly-based intrusion detection
  • Policy-based intrusion detection

You may also find similarities in their deployment methods. In fact, some IDS and IPS types are installed on endpoint devices. Finally, some IDS and IPS types inspect the same things, like wireless network traffic.

But how do they differ? The table below should help you visualize the differences between IDS vs IPS.

Scope of actionSending alertsSending alerts and taking action without human intervention
Main functionsDetects intrusions and sends alertsDetects potential intrusions and blocks them 
Optionally sends alerts
DeploymentPassive/out-of-band via a spanning port or network tapInline
AutonomyNo. Needs to send alerts to threat analystsYes
IDS vs IPS head to head!

Note: The differences in deployment only apply to network-based types of IDS and IPS, i.e., NIDS and NIPS. But these are out of scope for this article. That said, I must point out these differences because network-based IDS and IPS are the most widely used.

To sum up, an IDS detects intrusions, while an IPS blocks them. Additionally, an IDS can only help in preventing threats if you have security staff operating it. Conversely, an IPS can act autonomously.

Now that you know the similarities and differences between an IDS and an IPS, it’s time to discuss when you’d normally use one over the other

Should You Use IDS or IPS? 

Since an IPS can act autonomously, it might seem like the more advanced security tool and the better choice. That isn’t necessarily true, though. An IPS has a disadvantage. An IPS may block a legitimate business process if it runs across a false positive. For instance, your IPS may flag legitimate traffic as a threat. 

An IDS is less susceptible to these blunders. When it detects suspicious traffic, it sends it to a security analyst. The security analyst can then analyze the traffic and confirm whether it’s a threat. Of course, this means you should have a security analyst in the first place

When to Use an IDS

Generally, you’d use an IDS when you have in-house or third-party security analysts. An IDS is also necessary if you can’t afford to have your systems taken offline by a simple false positive. 

When to Use an IPS

On the other hand, if you don’t have security analysts and want something that acts autonomously, an IPS would be the better choice. An IPS is also essential when your systems can’t afford any threats. For example, you’d use an IPS to protect a database with lots of personal data. 

When to Use Both

All that being said, you’d ideally deploy an IDS and IPS together. Why? Consider this scenario: You have an IPS in front of a router facing an external network, say, the internet. Behind that router is a switch connecting to your internal network and an IDS connected to that switch’s spanning port. 

Diagram of a cloud (e.g., internal network) connecting to an IPS that then connects to a router, which then connects to a switch. On the other side of the switch, the following devices connect to it: 2 PCs , and IDS, and 2 servers.
An IPS paired with an IDS, an ideal setup!

Now, imagine you’ve configured the IPS with relatively lenient filtering rules. Conversely, you programmed the IDS with stringent filtering rules. What would happen in that case? The IPS would filter out defined unwanted traffic. It’ll also allow all other traffic, especially legitimate traffic, to pass through.

On the other hand, the IDS can detect and alert you of all suspicious traffic. That would include both true and false positives. And that’s okay because your security analysts are here to identify the false positives. After that, you can fine-tune your IDS and IPS accordingly until you reach your ideal configuration.

Final Thoughts

The main goal of this IDS vs IPS article was to help you understand the differences between IDS and IPS. By now, you should know that both IDS and IPS employ similar intrusion detection methods. But you should keep in mind that they aren’t the same. For instance, an IDS won’t take action autonomously to stop a threat. Conversely, an IPS will. 

This knowledge should help you decide which solution you’ll choose for your business. Ideally, you’d want to deploy both to create a robust defense against threats.

Do you have more questions about IDS vs IPS? Check out the FAQ and Resources sections below!


What is a DDoS attack?

A Distributed Denial of Service (DDoS) attack is a network-based attack. It aims to overwhelm the target’s computing resources. An attack like this can disrupt your network’s performance. In turn, it prevents legitimate users from connecting. However, certain types of IDS and IPS can directly or indirectly thwart a DDoS attack. 

What is incident response?

Incident response is the process of addressing a perceived threat. Generally, trained security staff will carry out an effective incident response plan. It usually comes into play after a threat has been detected by tools like an IDS or an IPS. 

What is a network tap?

A network tap is another way of connecting an IDS out of band. It’s a direct connection between the IDS and the physical network itself, e.g., a fiber optic cable. As with spanning ports, a network tap will allow you to view a copy of the network traffic transmitted over the media being tapped.

What is network flow?

Network flow refers to a set of packets passing through a point in the network over a particular time interval. Certain flow data may also provide insights for intrusion detection and prevention. Flow data is typically collected through protocols like NetFlow and sFlow.

What is Machine Learning?

Machine Learning (ML) is a field in computer science. ML focuses on using data and algorithms to mimic how humans learn. ML-based techniques are also used in modern intrusion detection and prevention systems. 


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