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PRTG NetFlow Filter Example

PRTG NetFlow Filter Example

NetFlow is a powerful network monitoring technology that enables network administrators to gain insights into the traffic and flow patterns on their network. PRTG, a comprehensive network monitoring tool, provides users with the ability to apply filters to NetFlow data, allowing for more targeted analysis and reducing the overall monitoring overhead. In this article, we will explore the concept of PRTG NetFlow filters and provide practical examples of their implementation.

1. Introduction

What is PRTG NetFlow?

PRTG is a popular network monitoring solution that supports NetFlow, a protocol developed by Cisco for collecting and analyzing network traffic data. NetFlow allows administrators to capture detailed information about network flows, including source and destination IP addresses, protocols, ports, and data volumes. PRTG’s integration of NetFlow provides users with real-time visibility into their network traffic, facilitating troubleshooting and performance optimization.

Importance of NetFlow Filtering

As networks grow in complexity, the volume of data generated by NetFlow can become overwhelming. NetFlow filtering becomes essential to focus on specific data of interest and reduce the sheer volume of information. By configuring filters, network administrators can zoom in on specific aspects of the network and obtain more meaningful insights.

2. Understanding PRTG NetFlow Filters

Definition of NetFlow Filters

NetFlow filters in PRTG act as rules that specify the criteria for selecting network flow data to be included or excluded from analysis. These filters can be based on various attributes, such as source or destination IP addresses, ports, protocols, and more. By setting up these filters, administrators can control which data is relevant for monitoring and reporting.

How NetFlow Filters Work in PRTG

When NetFlow data is collected, it passes through the configured filters. If a flow matches the criteria specified in a filter rule, it is included in the analysis. On the other hand, flows that do not meet the filter conditions are disregarded, saving valuable storage and processing resources.

3. Benefits of Using NetFlow Filters in PRTG

Optimizing Network Traffic Analysis

By applying filters to NetFlow data, administrators can narrow down their focus to specific network segments or devices. This level of granularity allows for deeper analysis of critical areas, such as high-traffic servers or important network links.

Reducing Network Monitoring Overhead

Unfiltered NetFlow data can be overwhelming, leading to unnecessary resource consumption. NetFlow filters help in minimizing this overhead by focusing only on relevant data, making the monitoring process more efficient.

Identifying and Isolating Network Issues

NetFlow filters aid in troubleshooting by isolating specific flows that might be causing network issues. By examining flows that meet certain criteria, administrators can quickly identify problematic areas and take corrective actions.

4. How to Set Up NetFlow Filters in PRTG

Accessing the PRTG Web Interface

To set up NetFlow filters in PRTG, access the web interface of the PRTG Network Monitor. Log in using your credentials to access the dashboard and configuration options.

Configuring NetFlow Sensor

Before setting up filters, ensure you have configured the NetFlow sensor in PRTG. The sensor should be actively collecting NetFlow data from the devices on your network.

Adding Filters for Specific Data

Once the NetFlow sensor is in place, navigate to the settings for the sensor. Under the “Filters” section, add rules based on your specific monitoring requirements. For example, you can create filters to monitor traffic from a particular IP address or filter data based on a certain port.

5. PRTG NetFlow Filter Examples

Filtering by Source IP Address

To analyze the traffic originating from a specific IP address, create a filter that includes only flows with that particular source IP address. This filter can help in monitoring the behavior of a critical server or identifying potential security threats.

Filtering by Destination Port

If you want to monitor traffic destined for a particular service, configure a filter based on the destination port number. This filter allows you to focus on traffic relevant to a specific application or service.

Filtering by Protocol Type

NetFlow filters can also be set up based on protocol type. For instance, you might want to examine all the HTTP traffic or focus on a specific protocol like TCP for detailed analysis.

6. Advanced NetFlow Filtering Techniques

Combining Multiple Filters

PRTG allows you to combine multiple filters to create complex rules for traffic analysis. This advanced filtering technique enables you to perform more targeted monitoring, such as traffic from a particular IP address to a specific port.

Using Time-Based Filters

Time-based filters are useful for monitoring specific time periods, such as peak hours or business-critical intervals. This allows administrators to focus on the network’s behavior during particular timeframes.

Setting Threshold-based Filters

Threshold-based filters trigger alerts when certain conditions are met. For example, you can set a filter to monitor excessive bandwidth utilization and receive an alert when the threshold is exceeded.

7. Best Practices for Using NetFlow Filters

Regularly Reviewing Filter Rules

Networks are dynamic, and filtering requirements may change over time. It’s essential to review and update filter rules periodically to ensure they remain relevant to the network’s evolving needs.

Monitoring Filter Performance

Monitoring the performance of NetFlow filters is crucial to identify any bottlenecks or performance issues related to the filtering process. Regular performance checks help maintain efficient filtering.

Adjusting Filters as Network Changes

As the network infrastructure changes or expands, filter rules may require adjustments. Be prepared to modify filters accordingly to accommodate new devices and traffic patterns.

8. Conclusion

PRTG NetFlow filters offer network administrators a powerful tool for efficiently monitoring and analyzing network traffic. By implementing appropriate filters, administrators can focus on the data that matters most, identify issues, and optimize network performance. The ability to set up complex rules and apply advanced filtering techniques empowers administrators to gain deeper insights into their networks.


1. Why is NetFlow filtering important in PRTG?

NetFlow filtering helps reduce the volume of data collected, enabling more targeted analysis and reducing monitoring overhead.

2. Can I create multiple filters in PRTG?

Yes, PRTG allows users to combine multiple filters for advanced and specific traffic analysis.

3. What are some common NetFlow filter examples?

Common examples include filtering by source IP address, destination port, and protocol type.

4. How often should I review my NetFlow filter rules?

It is recommended to review and update filter rules periodically to adapt to changing network conditions.

5. Can NetFlow filters help in troubleshooting network issues?

Yes, by isolating specific flows, NetFlow filters aid in identifying and resolving network problems effectively.

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