Understanding NIDS (Network Intrusion Detection Systems)

Network Intrusion Detection Systems (NIDS) are software applications that analyze network traffic patterns to identify potential threats. They are considered a core part of any robust cybersecurity system. With that in mind, here is a brief guide to what you need to know about NIDS.

What is an NIDS

There are two primary types of NIDS. These are network sensors and host-based intrusion detection systems (HIDS).

Network sensors are specialized devices or applications placed strategically at various network locations, like routers or switches. HIDS are software applications that are primarily used for monitoring traffic within the local host or specific services/applications.

Network sensors and HIDS can be used separately. It is, however, quite common to combine both forms of NIDS.

How NIDS work

Network Intrusion Detection Systems (NIDS) monitor selected data points within a network. They analyze network activities to identify irregular patterns that could indicate malicious behavior.

A NIDS’ main source of information is packet headers. These contain crucial information such as source and destination IP addresses, ports, and protocol types. It will also monitor the rate of transmitted packets per second. If this deviates from the expected transmission rates, the NIDS will alert system administrators.

How NIDS detect suspicious activities

NIDS use five main strategies to detect suspicious activities. These are:

• Signature-based detection: Looks for predefined signatures or patterns of known attacks.
• Stateful protocol analysis: Learns patterns indicating malicious activity without requiring prior knowledge of specific attacks.
• Behavioral-based detection: Utilizes behavioral analysis to identify potential threats.
• Anomaly-based detection: Focuses on detecting traffic deviating from expected norms.
• Heuristic-based detection: Utilizes problem-solving tactics to analyze patterns beyond known signatures.

These five strategies complement each other. The strengths of one tactic will generally cancel out the weaknesses of another tactic and vice versa. For example, signature-based detection is only effective against known threats. Known threats are, however, a significant portion of the threats networks have to mitigate. This means that signature-based detection is an effective way to eliminate a high percentage of threats using minimal resources.

By contrast, heuristic detection can protect against sophisticated attacks even when there is no prior knowledge of their operating mechanism. It is, however, challenging to configure appropriately. This means that it’s vulnerable to producing false positives as well as missing some threats. It is, therefore, currently, best used as a last line of defense rather than a first.

Stateful protocol analysis, behavioral-based detection, and anomaly-based detection sit in between these two extremes. They all require a baseline knowledge of network and user behavior to be effective. At the same time, none of these approaches is dependent on activity exactly matching known patterns.

NIDS deployment and management

It’s important to be clear on the fact that a NIDS is not a “set-and-forget” piece of technology. Once it has been deployed, it needs to be monitored, updated, and optimized to work effectively. Here are some key points to consider.

Pre-deployment considerations

Before you deploy your NIDS, you need to define and map your network architecture clearly. In particular, you need to identify your critical assets, choke points, and potential entry points for intruders. You also need to conduct a comprehensive analysis of potential threats to the network, identifying specific vulnerabilities and attack vectors.

This knowledge will allow you to allocate resources effectively for both hardware and software components. In other words, it will help to ensure that your NIDS deployment stays on budget and delivers value for money.

Monitoring and response

On the technical side, you will need to implement continuous monitoring of network traffic and real-time analysis of packet headers, statistics, and data flows. This is vital to maintain agility in threat response.

On the human side, you may need to provide training for network administrators so that they understand how to use the NIDS effectively. You may also need to update (or develop) a robust incident response plan outlining actions to be taken upon NIDS alerts.

Maintenance and optimization

It is vital that you keep signature databases up-to-date to ensure the NIDS recognizes the latest known threats.

It is highly desirable for you to conduct regular audits of NIDS configurations and rules to ensure alignment with evolving network dynamics. This will allow you to fine-tune NIDS performance parameters to balance detection accuracy and minimize false positives.

You may also need to provide ongoing training for network administrators to enhance their skills in managing and optimizing NIDS effectively.

Integrating NIDS with SIEM systems

In many cases, businesses deploying a NIDS will need (or want) to integrate it with a Security Information and Event Management (SIEM) system. Using an SIEM system means that all security-related logs and events are consolidated in a centralized repository. They can therefore be leveraged in a holistic manner rather than in silos. This often leads to much faster and more accurate responses to real threats. It also helps to reduce false positives.

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