PRTG Manual: NetFlow v9 (Custom) Sensor

Performance impact

This sensor has a very high performance impact. We recommend that you use no more than 50 of this sensor on each probe.

NetFlow

This sensor requires that the NetFlow export of the respective version is enabled on the target system. The target system must send the flow data stream to the IP address of the probe system.

Channels

This sensor does not officially support more than 50 channels.

Cluster probe

This sensor does not support cluster probes. You can only set it up on local probes or remote probes.

IPv6

This sensor supports IPv6.

Knowledge Base

Knowledge Base: What is the Active Flow Timeout in flow sensors?

Hosted probe

You cannot add this sensor to the hosted probe of a PRTG Hosted Monitor instance. If you want to use this sensor, add it to a remote probe device.

Receive Packets on UDP Port

Enter the User Datagram Protocol (UDP) port number on which PRTG receives the flow packets. It must match the UDP port number in the NetFlow export options of the hardware router device. Enter an integer.

When you configure the export, make sure that you select the appropriate NetFlow version for this sensor.

Sender IP Address

Enter the IP address of the sending device that you want to receive the NetFlow from. Enter an IP address to only receive data from a specific device or leave the field empty to receive data from any device on the specified port.

Receive Packets on IP Address

Select the IP addresses on which PRTG listens to NetFlow packets. The list of IP addresses is specific to your setup. To select an IP address, enable a check box in front of the respective line. The IP address that you select must match the IP address in the NetFlow export options of the hardware router device.

When you configure the export, make sure that you select the appropriate NetFlow version for this sensor.

You can also select all items or cancel the selection by using the check box in the table header.

Active Flow Timeout (Minutes)

Enter a time span in minutes after which the sensor must receive new flow data. If the timeout elapses and the sensor receives no new data during this time, it shows the Unknown status. Enter an integer. The maximum timeout is 60 minutes.

We recommend that you set the timeout one minute longer than the timeout in the hardware router device.

If you set this value too low, flow information might be lost.

For more information, see the Knowledge Base: What is the Active Flow Timeout in flow sensors?

If the target device sends incorrect time information that results in wrong monitoring data, try to use 0 as the active flow timeout. This ignores the start and stop information of a flow as provided by the device and accounts all data to the current point in time. It might result in spikes but the sensor captures all data.

Sampling Mode

Define if you want to use the sampling mode:

• Disable (default): Use the standard flow.
• Enable: Use the sampling mode and specify the Sampling Rate below.

This setting must match the setting in the xFlow exporter.

Sampling Rate

This setting is only visible if you select Enable above.

Enter a number that matches the sampling rate in your device that exports the flows. If the number is different, monitoring results will be incorrect. Enter an integer.

Channel Definition

Enter a channel definition to divide the traffic into different channels. Enter each definition in one line. The sensor accounts all traffic that you do not define a channel for to the default channel Other.

For more information, see section Channel Definitions for Flow, IPFIX, and Packet Sniffer Sensors.

Extensive use of many filters can cause load problems on the probe system. We recommend that you define specific, well-chosen filters for the data that you really want to analyze. We recommend that you do not use more than 20 channels in graphs and tables, and not more than 100 channels in total. For performance reasons, we recommend that you add several sensors with fewer channels each.

Stream Data Handling

Define what PRTG does with the stream and packet data:

• Discard stream data (default): Do not store the stream and packet data.
• Store stream data only for the 'Other' channel: Only store stream and packet data that is not otherwise filtered and is therefore accounted to the default Other channel. PRTG stores this data in the \StreamLog subfolder of the PRTG data directory on the probe system. The file name is Streams Sensor [ID] (1).csv. This setting is for debugging purposes. PRTG overwrites this file with each scanning interval.
• Store all stream data: Store all stream and packet data. This setting is for debugging purposes. PRTG overwrites this file with each scanning interval.

Use with caution. It can create huge data files. We recommend that you only use this setting for a short time.

Include Filter

Define if you want to filter any traffic. If you leave this field empty, the sensor includes all traffic. To include specific traffic only, define filters using a special syntax.

Exclude Filter

First, the sensor considers the filters in Include Filter. From this subset, you can explicitly exclude traffic, using the same syntax.

Primary Channel

Select a channel from the list to define it as the primary channel. In the device tree, PRTG displays the last value of the primary channel below the sensor's name. The available options depend on what channels are available for this sensor.

You can set a different primary channel later by clicking below a channel gauge on the sensor's Overview tab.

Graph Type

Define how this sensor shows different channels:

• Show channels independently (default): Show a graph for each channel.
• Stack channels on top of each other: Stack channels on top of each other to create a multi-channel graph. This generates a graph that visualizes the different components of your total traffic.
  You cannot use this option in combination with manual Vertical Axis Scaling (available in the channel settings).

Stack Unit

This setting is only visible if you select Stack channels on top of each other above.

Select a unit from the list. PRTG stacks all channels with this unit on top of each other. By default, you cannot exclude single channels from stacking if they use the selected unit. However, there is an advanced procedure to do so.

Primary Toplist

Define which Toplist is the primary Toplist of the sensor:

• Top Talkers
• Top Connections
• Top Protocols
• [Any custom Toplists you add]

PRTG shows the primary Toplist in maps when you add a Toplist object.

[Custom]

The traffic by type according to the channel definition

Downtime

In the channel table on the Overview tab, this channel never shows any values. PRTG uses this channel in graphs and reports to show the amount of time in which the sensor was in the Down status

Other

All traffic for which no channel is defined

Total

The total traffic

This channel is the primary channel by default.