Sensor of the Week: NetFlow V5 Sensor

 Originally published on October 06, 2014 by Florian Staffort
Last updated on March 03, 2022 • 8 minute read

The best way to monitor the traffic in your network depends on several factors. If you are the responsible administrator for a high traffic network which is equipped with a lot of Cisco devices, NetFlow is the ideal monitoring option. In flow monitoring, the router gathers bandwidth usage data (flows), aggregates these flows, and sends UDP packets with flow information back to PRTG Network Monitor.

The main advantage of NetFlow monitoring in comparison to packet sniffing is reduced CPU load on the PRTG core server system because of a smaller flow of data to PRTG compared to the monitored traffic due to sampling (optional) and pre-aggregation of traffic data.

NetFlow monitoring is a great way to keep an eye on your traffic, especially if you have limited resources and need to differentiate the bandwidth usage by IP addresses and/or network protocol.


PRTG offers monitoring possibilities for all NetFlow protocol versions, including the NetFlow V5 sensor. It receives traffic from a compatible device and enables you to analyze it by type. You can use its pre-configured filter options to divide traffic into different channels by choosing your desired traffic categories from a list when you add this sensor type to PRTG.

When you are enabling NetFlow export on your device, you only have to configure it to send the flow data stream to the IP address of the PRTG probe system running your NetFlow sensor. That's all you have to do to get your traffic monitoring started!


With NetFlow you can not only measure the total bandwidth usage, but break down the traffic by IP address, port, protocol, and other parameters. PRTG then displays the results in so-called toplists (see screenshot above). By default, there are three different toplists predefined for each sensor:

  • Top Connections shows bandwidth usage by connection,
  • Top Protocols shows bandwidth usage by protocol, and
  • Top Talkers shows bandwidth usage by IP address.

If you want to monitor devices that support other NetFlow versions, PRTG also offers sensors for NetFlow V9/IPFIX.

If you want to know more about the NetFlow V5 sensor and its settings, please take a look at the PRTG manual and, if your are interested in monitoring Cisco devices in general, why not find our more in our blog series?


All Sensors of the Week

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