Best NIDS Tools & Software

What is NIDS / Network Intrusion Detection Systems?

NIDS is the acronym for network intrusion detection system. NIDS detect nefarious behavior on a network such as hacking, port scanning and denial of service.

Here is our list of the best NIDS tools:

  1. SolarWinds Security Event Manager EDITOR’S CHOICE A HIDS package with NIDS features. This comprehensive security tool runs on Windows Server and can process packet capture files generated by Snort. Download the 30-day free trial.
  2. CrowdStrike Falcon Intelligence A threat intelligence service that monitors network traffic for security risks when it passes onto an endpoint.
  3. Snort The leading NIDS. This tool is free to use and runs on Windows, Linux, and Unix.
  4. Zeek Previously known as Bro, this is a highly respected free NIDS that operates at the Application layer.
  5. Suricata This tool applies both anomaly-based and signature-based detection methodologies.
  6. IBM QRadar This cloud-based SIEM tool combines HIDS and NIDS capabilities.
  7. Security Onion A compendium of functions drawn in from other open-source HIDS and NIDS tools.
  8. Open WIPS-NG A free tool for defending wireless networks.
  9. Sagan A HIDS that can operate as a NIDS, given a live data feed for input.
  10. Splunk A widely-used traffic analyzer with HIDS and NIDS capabilities.

The purpose of NIDS

Intrusion detection systems look for patterns in network activity to identify malicious activity. The need for this category of security system arose because of changes in hacker methods in reaction to earlier successful strategies to block malicious activities.

Firewalls have become very effective at blocking inbound connection attempts. Antivirus software has successfully identified infections carried through USB sticks, data disks, and email attachments. With traditional malicious methods blocked, hackers turned to attack strategies such as Distributed Denial of Service (DDoS) attacks. Edge services now make those attack vectors less threatening.

Today, the Advanced Persistent Threat (APT) is the biggest challenge to network managers. These attack strategies are even now used by national governments as part of hybrid warfare. In an APT scenario, a group of hackers gain access to a corporate network and use the resources of the company for their own purposes as well as getting access to company data for sale.

The collection of personal data held on company databases has become a profitable business, thanks to data agencies. That information can also be used for malicious purposes and can also feed back into access strategies through doxing. The information available on company customer, supplier, and employee databases are useful resources for whaling and spearphishing campaigns. These methods have been used effectively by con artists to trick company employees into transferring money or disclosing secrets personally. These methods can be used to blackmail company workers into acting against the interests of their employers.

Disgruntled employees also present problems for corporate data security. A lone worker with network and database access can wreak havoc by using authorized accounts to cause damage or steal data.

So, network security now has to encompass methods that go far beyond blocking unauthorized access and preventing the installation of malicious software. Network-based intrusion detection systems offer very effective protection against all hidden intruder activity, malicious employee activity, and con artist masquerading.

What is the difference between NIDS and SIEM?

When seeking new security systems for your network, you will encounter the term SIEM. You may wonder whether this means the same as NIDS.

There is a great deal of overlap between the definitions of SIEM and NIDS. SIEM stands for Security Information and Event Management. The field of SIEM is a combination of two pre-existing categories of protection software. There are Security Information Management (SIM) and Security Event Management (SEM).

The field of SEM is very similar to that of NIDS. Security Event Management is a category of SIEM that focuses on examining live network traffic. This is exactly the same as the specialization of network-based intrusion detection systems.

What is the difference between NIDS and HIDS?

Network-based intrusion detection systems are part of a broader category, which is intrusion detection systems. The other type of IDS is a host-based intrusion detection system or HIDS. Host-based intrusion detection systems are roughly equivalent to the Security Information Management element of SIEM.

While network-based intrusion detection systems look at live data, host-based intrusion detection systems examine the log files on the system. The benefit of NIDS is that these systems are immediate. By looking at network traffic as it happens, they can take action quickly. However, many activities of intruders can only be spotted over a series of actions. It is even possible for hackers to split malicious commands between data packets. As NIDS works at the packet level, it is less capable of spotting intrusion strategies that spread across packets.

HIDS examines event data once it has been stored in logs. Writing records to log files creates delays in responses. However, this strategy allows analytical tools to detect actions that take place at several points on a network simultaneously. For example, if the same user account is used to log in to the network from dispersed geographical locations and the employee allocated that account is stationed in none of those places, then clearly the account has been compromised.

Intruders know that log files can expose their activities and so removing log records is a defensive strategy used by hackers. The protection of log files is, therefore, an essential element of a HIDS system.

Both NIDS and HIDS have benefits. NIDS produces quick results. However, these systems need to learn from a network’s normal traffic to prevent them from reporting “false positives.” Particularly in the early weeks of operation on a network, NIDS tools have a tendency to over-detect intrusion and create a flood of warnings that prove to be highlighting regular activity. On the one hand, you don’t want to filter out warnings and risk missing intruder activity. However, on the other hand, an overly-sensitive NIDS can try the patience of a network administration team.

HIDS gives a slower response but can give a more accurate picture of intruder activity because it can analyze event records from a wide range of logging sources. You need to take the SIEM approach and deploy both a NIDS and a HIDS to protect your network.

Network Intrusion Detection Systems detection methods

NIDS use two basic detection methods:

  • Anomaly-based detection
  • Signature-based detection

Signature-based strategies arose from the detection methods used by antivirus software. The scanning program looks for usage patterns in network traffic including byte sequences and typical packet types that are regularly used for attacks.

An anomaly-based approach compares current network traffic to typical activity. So, this defense strategy requires a learning phase that establishes a pattern of normal activity. An example of this type of detection would be the number of failed login attempts. A human user might be expected to get a password wrong a few times, but a brute-force programmed intrusion attempt would use many password combinations cycling through a rapid sequence. That is a very simple example. In the field, the activity patterns that an anomaly-based approach looks for can be very complicated combinations of activities.

Intrusion detection and intrusion prevention

Spotting intrusion is step one of keeping your network safe. The next step is to do something to block the intruder. On a small network, you could possibly enact manual intervention, updating firewall tables to block intruder IP addresses and suspending compromised user accounts. However, on a large network, and on systems that need to be active around the clock, you really need to roll through threat remediation with automated workflows. Automatic intervention to address intruder activity is the defining difference between intruder detection systems and intruder prevention systems (IPS).

Fine-tuning of the detection rules and the remediation policies is vital in IPS strategies because an over-sensitive detection rule can block out genuine users and shut down your system.

The best Network Intrusion Detection Systems tools & software

This guide focuses on NIDS rather than HIDS tools or IPS software. Surprisingly, many of the leading NIDS are free to use and other top tools offer free trial periods.

Our methodology for selecting a network-based intrusion detection system 

We reviewed the market for NIDS packages and analyzed the tools based on the following criteria:

  • Live traffic analysis
  • Packet inspection
  • Anomaly detection
  • A threat intelligence feed
  • Triage to speed up processing and reduce CPU usage
  • A free trial or a free tool that provides a risk-free assessment opportunity
  • Value for money from a tool that provides adequate security and is offered at a fair price or a free tool that is worth installing

With these selection criteria in mind, we looked for competent network intrusion detection systems that have good reputations and have proven track records.

1. SolarWinds Security Event Manager (FREE TRIAL)

Solarwinds Log and Event Manager

The SolarWinds Security Event Manager is mainly a HIDS package, but you can use NIDS functions with this tool as well. The tool can be used as an analytical utility to process data collected by Snort. You can read more about Snort below. Snort can capture traffic data that you can view through the Security Event Manager.

Key Features:

  • Both NIDS and HIDS features
  • Takes Snort feeds
  • Event correlation
  • Automated responses
  • Threat alerts

The combination of NIDS and HIDS makes this a really powerful data security software. The NIDS section of the Security Event Manager includes a rule base, called event correlation rules, that will spot activity anomalies that indicate an intrusion. The tool can be set to automatically implement workflows on the detection of an intrusion warning. These actions are called Active Responses. The actions that you can get automatically launched on the detection of an anomaly include: stopping or launching of processes and services, suspension of user accounts, blocking of IP addresses, and notification sending by email, SNMP message, or screen record. Active responses make the SolarWinds Security Event Manager into an intrusion prevention system.


  • A combination HIDS/NIDS tool, giving it more flexibility than competing products
  • Simple log filtering, no need to learn a custom query language
  • Dozens of templates and rules allow administrators to start using SEM with little setup or customization
  • Historical analysis tool helps find anomalous behavior and outliers on the network
  • Cross-platform with Windows, Mac, and most nix distributions


  • SEM Is an advanced NIDS product built for security professionals, requires time to fully learn the platform

This is the top-of-the-line IDS available on the market today and it is not free. The software will only run on the Windows Server operating system, but it can collect data from Linux, Unix, and Mac OS as well as Windows. You can get the SolarWinds Security Event Manager on a 30-day free trial.


The SolarWinds Security Event Manager is our top choice NIDS tool because it deploys HIDS techniques with NIDS capabilities. Using a live feed into the SEM creates a NIDS, while still making the file searching functions of the tool available to protect the network. Threat mitigation actions can be set up so that they are automatically implemented by the tool.

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OS: Windows 10 and later, Windows Server 2012 and later, Cloud-based: Hypervisor, AWS and MS Azure

2. CrowdStrike Falcon Intelligence

CrowdStrike Falcon Intelligence - Indicator Graph view

Although a NIDS typically monitors passing network traffic, CrowdStrike Falcon Intelligence operates on endpoints, catching traffic as it enters the device. Theoretically, this residence should make Falcon Intelligence a host-based intrusion detection system. However, the service operates on live data and not by reading through log files, so it is a NIDS.

Key Features:

  • Collects traffic from endpoints
  • Yara and Snort rules
  • Managed security service option
  • Anomaly-based detection

Falcon Intelligence is able to adapt other NIDS systems through the creation of rules that can be run in Yara and Snort. Those rules are generated in the Falcon Intelligence service and then checked and adjusted manually by a human cybersecurity expert at CrowdStrike HQ. Most of the Falcon Intelligence processes are automated. However, the highest plan of the service includes an allocated cybersecurity analyst. That plan is called Falcon Intelligence Elite. An intermediate plan that includes tailored internet scanning for mentions of your company is called Falcon Intelligence Premium. The base plan is just known as Falcon Intelligence and it includes threat intelligence hunting performed automatically on each endpoint on your network.


  • Doesn’t rely on only log files to threat detection, uses process scanning to find threats right away
  • Acts as a HIDS and endpoint protection tool all in one
  • Can track and alert anomalous behavior over time, improves the longer it monitors the network
  • Can install either on-premise or directly into a cloud-based architecture
  • Lightweight agents won’t slow down servers or end-user devices


  • Would benefit from a longer trial period

The Falcon Intelligence system is written on the CrowdStrike Falcon platform. This is mainly resident on the CrowdStrike server and offered as a cloud service with a user console accessed through a browser. Each protected endpoint also needs to have an agent program installed on it. That agent provides all data collection and mitigation procedures automatically. CrowdStrike offers a 15-day free trial of Falcon Intelligence.

3. Snort

Snort 3.0 with ElasticSearch LogStash and Kibana (ELK)

Snort, owned by Cisco Systems, is an open source project and is free to use. This is the leading NIDS today and many other network analysis tools have been written to use its output. The software can be installed on Windows, Linux, and Unix.

Key Features:

  • Free to use
  • Packet sniffer
  • Detection rules language

This is actually a packet sniffer system that will collect copies of network traffic for analysis. The tool has other modes, however, and one of those is intrusion detection. When in intrusion detection mode, Snort applies “base policies,” which is the detection rule base of the tool.

Base policies make Snort flexible, extendable, and adaptable. You need to fine-tune the policies to suit your network’s typical activities and reduce the incidences of “false positives.” You can write your own base policies, but you don’t have to because you can download a pack from the Snort website. There is a very large user community for Snort and those users communicate through a forum.


  • Completely free and open source
  • Large community shares new rule sets and configurations for sysadmins to deploy in their environment
  • Supports packet sniffing for live traffic analysis in conjunction with log scanning


  • Reliant on the community for support
  • Has a steeper learning curve than other products with dedicated support
  • Can require more policy tuning to eliminate false positives

Expert users make their own tips and refinements available to others for free. You can also pick up more base policies from the community for free. As there are so many people using Snort, there are always new ideas and new base policies that you can find in the forums.

4. Zeek

Zeek logs viewed via Dynamite Analitics app - Threats view

Zeek (formerly Bro) is a NIDS, like Snort, however, it has a major advantage over the Snort system – this tool operates at the Application Layer. This free NIDS is widely preferred by the scientific and academic communities.

Key Features:

  • Application Layer analysis
  • Both signature and anomaly detection
  • Free to use

This is both a signature-based system and it also uses anomaly-based detection methods. It is able to spot bit-level patterns that indicate malicious activity across network packets.

The detection process is handled in two phases. The first of these is managed by the Event Engine. As data is assessed at higher than packet level, analysis cannot be performed instantly. There has to be a level of buffering so that sufficient packets can be assessed together. So, Zeek is a little slower than a typical packet-level NIDS but still identifies malicious activity quicker than a HIDS. Collected data is assessed by policy scripts, which is the second phase of the detection process.


  • Highly customizable NIDS, designed specifically for security professionals
  • Supports application layer traffic analysis as well as log-based scanning
  • Utilizes signature detection and anomalous behavior scanning to detect known and unknown threats
  • Supports automation through scripting, allowing admins to script different actions easily


  • Only available for Unix, Linux, and Mac
  • Not as user friendly, requires deep knowledge of SIEMs, NIDS, DPI, etc
  • Better suited for researchers and specialists

It is possible to set up remediation actions to be triggered automatically by a policy script. This makes Bro an intrusion prevention system. The intrusion detection software can be installed on Unix, Linux, and Mac OS. Zeek can be deployed in conjunction with Dynamite-NSM, a free Network Security Monitor, to expand its capabilities and to take advantage of their advanced graphical displays of log data.

5. Suricata

Suricata Alerts - viewed in Dynamite Analitics console

Suricata is also a NIDS that operates at the Application Layer, giving it multi-packet visibility. This is a free tool that has very similar capabilities to those of Bro. Although these signature-based detection systems work at the Application level, they still have access to packet details, which lets the processing program get protocol-level information out of packet headers. This includes data encryption, Transport Layer and Internet Layer data.

Key Features:

  • Application Layer analysis
  • Free to use
  • Compatible with Snort

This IDS also employs anomaly-based detection methods. Apart from packet data, Suricata can examine TLS certificates, HTTP requests, and DNS transactions. The tool is also able to extract segments from files at bit-level for virus detection.


  • Collects data at the application layers, giving it unique visibility where products like Snort can’t see
  • Analyzes and reassembles protocol packets very efficiently
  • Can monitor multiple protocols and check the integrity of certificates in TLS, HTTP, and SSL
  • Is compatible with other tools that use the VRT rule format


  • Built-in scripting could be easier to use
  • Is free, but doesn’t have as large of a community as tools like Snort or Zeek
  • Could have an easier to navigate home dashboard

Suricata is one of the many tools that are compatible with the Snort data structure. It is able to implement Snort base policies. A big extra benefit of this compatibility is that the Snort community can also give you tips on tricks to use with Suricata. Other Snort-compatible tools can also integrate with Suricata. These include Snorby, Anaval, BASE, and Squil.

6. IBM QRadar

IBM QRadar

This IBM SIEM tool is not free, but you can get a 14-day free trial. This is a Cloud-based service, so it can be accessed from anywhere. The system covers all aspects of intrusion detection including the log-centered activities of a HIDS as well as the examination of live traffic data, which also makes this a NIDS. The network infrastructure that QRadar can monitor extends to Cloud services. The detection policies that highlight possible intrusion are built into the package.

Key Features:

  • SIEM
  • SaaS package
  • AI-driven anomaly-based detection

A very nice feature of this tool is an attack modeling utility that helps you test your system for vulnerabilities. IBM QRadar employs AI to ease anomaly-based intrusion detection and has a very comprehensive dashboard that integrates data and event visualizations. If you don’t want to use the service in the Cloud, you can opt for an on-premises version that runs on Windows.


  • Flexible cloud-based NIDS, making it easy to monitor from anywhere
  • Simple yet informative visualizations that are highly customizable
  • Features built-in attack modeling, great for penetration tests and vulnerability scans
  • Supports a Windows-based on-premise version for those not wanting a SaaS


  • Would like to see a longer 30-day trial for testing
  • Is expensive when compared to similar tools
  • Designed for enterprise use, smaller networks may find QRadar overwhelming or cost-prohibitive

7. Security Onion

Security Onion screenshot

If you want an IDS to run on Linux, the free NIDS/HIDS package of Security Onion is a very good option. This is an open-source project and is community-supported. The intrusion detection software for this tool runs on Ubuntu and was drawn in from other network analysis utilities.

Key Features:

  • A collection of tools
  • Free to use
  • HIDS and NIDS

A number of the other tools listed in this guide are integrated into the Security Onion package: Snort, Zeek, and Suricata. HIDS functionality is provided by OSSEC and the front end is the Kibana system. Other well-known network monitoring tools that are included in Security Onion include ELSA, NetworkMiner, Snorby, Squert, Squil, and Xplico.

The utility includes a wide range of analysis tools and uses both signature and anomaly-based detection techniques. Although the reuse of existing tools means that Security Onion benefits from the established reputation of its components, updates to elements in the package can be complicated.

Security Onion in kibana

You can use Kibana with Security Onion for enhanced threat detection.


  • Free open-source software
  • Highly detailed, designed for forensic-level analysis
  • Features built-in packet sniffer and options for traffic replay


  • Only available for Linux
  • Relies on Kibana for visualization, would like to see a default built-in option
  • The interface is not user friendly

8. Open WIPS-NG

OpenWIPS-NG screenshot

Open WIPS-NG is an open source project that helps you to monitor wireless networks. The tool can be used as a straightforward wifi packet sniffer or as an intrusion detection system. The utility was developed by the same team that created Aircrack-NG – a very famous network intrusion tool used by hackers. So, while you are using Open WIPS-NG to defend your network, the hackers that you spot will be harvesting your wireless signals with its sister package.

Key Features:

  • Wireless packet sniffer
  • Free tool
  • Automated responses

This is a free tool that installs on Linux. The software package includes three components. These are a sensor, a server, and an interface. Open WIPS-NG offers a number of remediation tools, so the sensor acts as your interface to the wireless transceiver both to collect data and to send out commands.


  • Highly flexible tool, developed by the hacking community
  • Lightweight command-line interface
  • Easy to memorize syntax
  • Completely open-source project


  • Not beginner-friendly
  • Designed primarily for security specialists
  • Relies on other tools to expand the functionality
  • Natively only available for Linux systems

9. Sagan

Sagan screenshot

Sagan is a HIDS. However, with the addition of a data feed from Snort, it can also act as a NIDS. Alternatively, you can use Bro or Suricata to collect live data for Sagan. This free tool can be installed on Unix and Unix-like operating systems, which means that it will run on Linux and Mac OS, but not on Windows. However, it can process Windows event log messages. The tool is also compatible with Anaval, BASE, Snorby, and Squil.

Key Features:

  • Free tool
  • HIDS
  • Get network feed from Snort

Useful extras built into Sagan include distributed processing and an IP address geolocator. This is a good idea because hackers often use a range of IP addresses for intrusion attacks but overlook the fact that the common location of those addresses tells a tale. Sagan can execute scripts to automate attack remediation, including the ability to interact with other utilities such as firewall tables and directory services. These abilities make it an intrusion prevention system.


  • Entirely free log analysis tool
  • Is compatible with other open-source tools like Zeek and Snort
  • Features an IP address locator which can give geopolitical information on addresses


  • Not available for Windows operating systems
  • Has a fairly sharp learning curve for new users
  • The interface can get cluttered quickly during scanning

10. Splunk

Splunk Screenshot

Splunk is a popular network traffic analyzer that also has NIDS and HIDS capabilities. The tool can be installed on Windows and on Linux. The utility is available in three editions. These are Splunk Free, Splunk Light, Splunk Enterprise, and Splunk Cloud. You can get a 15-day trial to the Cloud-based version of the tool and a 60-day free trial of Splunk Enterprise. Splunk Light is available on a 30-day free trial. All of these versions include data collection abilities and anomaly detection.

Key Features:

  • On-premises or cloud
  • NIDS and HIDS
  • Anomaly detection with AI

Security features of Splunk can be enhanced with an add-on, called Splunk Enterprise Security. This is available on a 7-day free trial.

This tool enhances the accuracy of anomaly detection and reduces the incidences of false positives through the use of AI. The extent of the alerting system can be adjusted by warning severity level to prevent your system administration team from getting swamped by an overzealous reporting module.

Splunk integrates log file reference to enable you to get a historical perspective on events. You can spot patterns in attacks and intrusion activity by looking at the frequency of malicious activity over time.


  • Cross-platform for both Windows and Linux operating systems
  • Can be installed in the cloud, or on-premise
  • Utilizes AI to identify anomalous behavior and eliminate false positives
  • Excellent reporting and dashboard options


  • Designed for large enterprise networks, can be more than what smaller networks need
  • More expensive than most NIDs tools on the market
  • Comes with a steep learning curve, specifically with the search language function
  • Onboarding and be complicated and time-consuming

Implementing NIDS

The risks that threaten your network security are now so comprehensive that you really don’t have a choice on whether or not to implement network-based intrusion detection systems. They are essential. Fortunately, you do have a choice over which NIDS tool you install.

All of the tools on the list are either free to use or are available as free trial offers. You will be able to take a couple of them through their paces. Simply narrow down the list further according to the operating system and then assess which of the shortlist features match the size of your network and your security needs.

Do you use a NIDS tool? Which did you choose to install? Have you also tried out a HIDS tool? How would you compare the two alternative strategies? Leave a message in the Comments section below and share your experience with the community.

Network Intrusion Detection Systems (NIDS) FAQs

Can NIDS and IPS work together?

Yes. NIDS and IPS work together very well. In fact, an IPS is just an IDS with extras. While an intrusion detection system spots unauthorized activity, an intrusion prevention system detects activity and then implements actions to shut that activity down. As an IPS has an IDS bundled into it, you don’t need to buy a separate IDS if you already have an IPS.

What does a network intrusion detection system do when it detects an attack?

Typically, an intrusion detection system is designed to identify anomalous behavior and raise an alert to draw attention to it. If you want a tool that will trigger remedial action on identifying an intrusion, you should be looking for an intrusion prevention system (IPS).

Where should a NIDS be placed to protect the entire network?

A NIDS needs to have access to all packets traveling around a network. In general, every packet passing over a network visits every device on it – it is just that the network adapter on each device ignores packets that aren’t addressed to it. So, the NIDS can be hosted on any device on the network just as long as that device’s network adapter has been placed in promiscuous mode to pay attention to all packets, not just those addressed to that device. If the network has several separate segments, such as with a demilitarized zone configuration, you can either host the NIDS on a connecting device, such as the router, or place a collector on the other segment that will communicate with the processing module resident on a host connected to the main network. A NIDS can also examine packets on a remote network if it has an agent installed there.

Image: Hacker Cyber Crime from PixabayPublic Domain.