Using ntopng with n2disk

When it comes to troubleshoot a network issue or analyse a security event, going back in time and drilling down to the packet level could be crucial to find the exact network activity that caused the problem. Continuous traffic recording provides a window into network history, that allows you to retrieve and analyse all the raw traffic in that period of time.

Enabling Traffic Recording

ntopng, since version 3.7, includes support for continuous traffic recording leveraging on n2disk, an optimized traffic recording application part of the ntop suite available on Linux systems.

In order to be able to enable this feature:

  1. both ntopng and n2disk need to be installed from packages.
  2. n2disk should be licensed according to the required dump speed. There is an ntopng Bundle license that allows you to license both with a single, convenient license.
  3. ntopng and n2disk should be installed and running on the same host to get a copy of the same traffic and be able to interact (access the same file system).

In order to install n2disk (we assume that you already configured the ntop repository and have ntopng installed) run the below commands according to your Linux distribution:


apt-get install n2disk


yum install n2disk

Please make sure that ntopng is running using the ntopng user, which is the default since version 3.7, as reported in this notice.

In order to use n2disk a license is also required, you can get one at e-shop or, if you are no-profit, research or an education institution please read this. The n2disk license can be installed directly from ntopng through the Preferences, Traffic Recording menu. The same page also provides the installed n2disk version and SystemID, both required to generate the license.


ntopng Enterprise L already includes a n2disk 1 Gbit license, there is no need to buy a n2disk license if a ntopng Enterprise L license is installed.

Traffic Recording License

The Traffic Recording Preferences Page

At this point you are ready to start recording traffic. Packets are dumped to disk using the industry standard Pcap file format. The default folder for pcap files is the ntopng data directory, under the “pcap” folder of a specific network inteface id (e.g. /var/lib/ntopng/0/pcap), however it is possible to replace the /var/lib/ntopng root folder with a different one adding –pcap-dir <path> to the ntopng configuration file.


For Continuous Traffic Recording with ZC or FPGA adapters please read the ZC/FPGA Support section.

In order to actually start recording traffic, you need to select an interface from the Interfaces menu, click on the disk icon, and configure the recording instance:

  1. Select “Continuous Traffic Recording”
  2. Configure the desired “Max Disk Space” value. This lets you control the maximum disk space to be used for pcap files, which also affects the data retention time (when the maximum disk space is exceeded, the oldest pcap file is overwritten). Please note that the data retention time also depends on the traffic throughput of the networks being monitored.
  3. Press the “Save Settings” button to actually start recording.
Traffic Recording

The Traffic Recording Page

At this point a new badge should appear on the top status bar. When the badge is blue, it means that traffic recording is running. Instead, when the badge is red, it means that there is a failure.

Traffic Recording Badge

The Traffic Recording Badge in the Footer

It is possible to get more information about the n2disk service status by clicking on the badge. The status page provides information including the uptime of the recording service, statistics about processed traffic, the log trace.

Traffic Recording Status

The Traffic Recording Status Page

External Traffic Recording Providers

One can manage n2disk services manually using the command line. In this case, one can configure ntopng to bind to an external traffic recording provider. Traffic recording providers are configured from the interface settings page. A dropdown menu with the list of available recording providers is shown.

Traffic Recording External Providers Selection

The Selection of External Traffic Recording Providers


In case n2disk processes are managed manually using configuration files, ntopng will not show a settings tab nor it will allow any configuration change. However, extractions will still be possible as described in the following section.

Traffic Extraction

All pcap files dumped to disk are indexed on-the-fly by n2disk to improve traffic extraction speed when recorded data need to be retrieved. It is possible to extract traffic from multiple places in ntopng, including the interface and the host Historical Traffic Statistics pages.

After enabling continuous traffic recording on an interface, a new button for extracting traffic appears at the top right corner of the Historical Traffic Statistics page.

Extract pcap button

The Extract Pcap Button in the Interface Historical Traffic Statistics page

Extract pcap button

The Extract Pcap Button in the Host Historical Traffic Statistics Page

By clicking on the button, a dialog box will let you run an extraction to retrieve the traffic matching the time interval selected on the chart. It is possible to download the extracted traffic directly (this should be used when the expected amount of extracted traffic is low) or queue the extraction job to process traffic in background (this should be used for extractions taking too long, or to archive extracted data on the machine running ntopng).

Extract pcap dialog

The Extract Pcap Dialog

In addition to the time constraint, it is possible to configure a BPF-like filter, to further reduce the extracted amount of data, by clicking on the Advanced. button The filter format is described at Packet Filtering.

Extract pcap dialog filter

The Extract Pcap Dialog Filter

The extraction button is also available in several other places while browsing the historical data, an example is the list of the Top Receivers or Top Senders available at the bottom of the Interface Historical Traffic Statistics page. In this case, a button on the right side of the row lets you download the traffic matching a specific host in the selected time interval.

Extract pcap button

The Extract Pcap Button in the Top Receivers in the Interface Historical Traffic Statistics Page

When an extraction job is scheduled for background processing by selecting the Queue as Job option, ntopng extracts the traffic and creates new pcap files with the traffic. This usually requires a few seconds, depending on a few factors, including: the time interval, the amount of recorded data, the extraction filter.

A reference for the extraction job (a link to the Traffic Extraction Jobs page with the list of scheduled extractions, and the extraction ID) is provided after starting the extraction, in order to control the status and download the pcap file(s) as soon as the extraction is completed. Extraction jobs can be stopped anytime using the Stop button, in case of extractions taking too long, or removed using the Delete button (this will also delete the corresponding pcap files).

Traffic Extraction Jobs

The Traffic Extraction Jobs page

It is possible to access the Traffic Extraction Jobs page also by clicking on the badge that appears on the top status bar when there is at least one extraction job scheduled.

Traffic Extraction Jobs Badge

The Traffic Extraction Jobs Badge in the Top Status Bar


The pcap file can also be downloaded directly through http, running a live extraction. It is possible to use a command line tool such as wget or curl for this. The direct URL for downloading the pcap is http://<ntopng IP>:3000/lua/rest/get/pcap/live_extraction.lua?ifid=<id>&epoch_begin=<epoch>&epoch_end=<epoch>[&bpf_filter=<filter>]


  • ifid is the interface Id as reported by ntopng in the interface page
  • epoch_begin is the start of the time interval to be extracted (epoch)>
  • epoch_end is the end of the time interval to be extracted (epoch)>
  • bpf_filter is a filter in nBPF format

Please note that you should use cookies for authentication, as explained in the documentation. For example with curl you can specify username and password with --cookie "user=<user>; password=<password>"

Command line tools are useful for example to process a pcap stream and pipe it to an analysis tool such as tcpdump or tshark/wireshark. For example, to process the extracted traffic directly with wireshark, it is possible to use curl as in the example below:

curl -s --cookie "user=admin; password=admin" "" | wireshark -k -i -

ZC/FPGA Support

If you need to process traffic at high rate at 10/40Gbit and above, you are probably looking for capture technologies like PF_RING ZC for Intel or FPGA adapters.

As both PF_RING ZC and FPGA adapters are based on kernel bypass, the drawback is that they do not allow you to capture the same stream from multiple applications at the same time. This means that you cannot run ntopng for traffic analysis and n2disk for raw traffic recording at the same time on the same interface.

In order to overcome this, n2disk is able to export flow metadata to ntopng over ZMQ, similar to what nProbe does as explained in the Using ntopng with nProbe section. As depicted below, in this configuration n2disk can be configured to capture raw packets, dump PCAP data to disk, and export flow metadata in JSON format through ZMQ to ntopng at the same time.

Support for n2disk ZMQ export

Support for n2disk ZMQ export

Following is a sample configuration of n2disk and ntopng to achieve what has been depicted above. This example assumes that both n2disk and ntopng are running on the same host.

ntopng Configuration File

In order to process flow metadata through ZMQ in ntopng, you need to add a collector interface to the configuration file (/etc/ntopng/ntopng.conf):


n2disk Configuration File

The ntopng endpoint should be added to the n2disk configuration file (e.g. /etc/n2disk/n2disk-nt01.conf) using the --zmq option. The --zmq-probe-mode option (if ntopng is running as a collector like in this example: notice the small c in the ntopng endpoint) and the --zmq-export-flows option (to export flow metadata in addition to traffic statistics) are also required.

It is a good practice to run n2disk using the ntopng user (see -u) in order to make sure that ntopng is able to access the PCAP data recorded by n2disk and run traffic extractions.

Please see the n2disk User’s Guide for further information about the other options. Please note that in the example below n2disk is aggregating traffic in hardware from 2 ports of a Napatech adapter, please see the Napatech configuration for configuring the adapter.


At this point you should start both the ntopng service (e.g. systemctl start ntopng) and the n2disk service (e.g. systemctl start n2disk@nt01), and configure the n2disk instance as external PCAP source for the collector interface as explained in the External Traffic Recording Providers section in order to be able to check the n2disk service status and run traffic extractions.