10. Flows Dump

Ntopng can dump expired flow information either to a MySQL database or ElasticSearch. Ntopng is instructed to dump expired flows to MySQL via the -F startup modifier.

10.1. MySQL

To dump flows to MySQL ntopng requires the -F modifier followed by a string in the following format:

mysql;<host|socket>;<dbname>;<table name>;<user>;<pw>

The string has 6 semi-colon separated fields:

  • mysql tells ntopng to dump flows to MySQL
  • <host|socket> is the host (or the socket) of a running MySQL instance that will receive expired flows
  • <dbname> specify the name of the MySQL database to use. If the database does not exist, ntopng will create it.
  • <table name> specify the prefix of MySQL table names to use. Presently the prefix is always defaulted to flows.
  • <user>;<pw> are the credential of a MySQL user that has privileges to create, select and update tables on <dbname>.

Ntopng creates two database tables. Tables are named flowsv4 and flowsv6 that are used to store IPv4 and IPv6 flows, respectively.

MySQL flows dump

A MySQL Table with Dumped Flows

By enabling MySQL integration, it’s also possible to inspect the past flows via the ntopng Historical Explorer, which provides many filters and drillown capabilities.

MySQL Historical Explorer

Historical Explorer

For a complete discussion on the explorer capabilities check out the following URLs:

10.2. MySQL Performance

Tuning MySQL parameters is an essential task to avoid dropped flows. The dropped flows percentage is shown into the Network Interface overview page.

MySQL Export Statistics

MySQL Export Statistics

Here are some tips to tune MySQL:

  • key_buffer_size: typically, this is set to 30-40% of the available RAM memory. Ideally, the sum of the sizes of all the .MYI files should be smaller than key_buffer_size but this is not always doable nor practical. Default size is just 8M so an increase would definitely be beneficial.
  • sort_buffer_size: this can have positive effects on the search queries rather than on the insertion. The status variable sort_message_passes is the only one that uses sort_buffer_size. You should check the sort_message_passes and if it is a large number then an increase in the sort_buffer_size will have a positive effect.

To improve performance, it’s also important to set an appropriate retention time on data, because the more data MySQL has, the more it slows down. This can be configured from the “MySQL storage” preference into the Timeseries settings tab. Old data to delete is checked on a daily basis.

MySQL Retention Preference

MySQL Retention Preference

The followings are the expected MySQL flow export rates with ntopng, assuming a fast disk and CPU are used:

  • ~2k flows/sec (ntopng community, professional)
  • ~10k flows/sec (ntopng enterprise)

10.3. ElasticSearch

Elasticsearch is an Open-Source real-time search and analytics engine with a powerful RESTful API built on top of Apache Lucene. Ntopng can connect to an external Elasticsearch cluster as client using the Bulk insert API for JSON mapped indexing.

Elasticsearch is designed for quickly and dynamically analyzing or searching through large amounts of data and thus is ideal for flows generated by ntopng, enabling users and integrators to create a virtually infinite number and variety of statistics using Kibana.

To learn more about Elasticsearch visit: https://www.elastic.co/guide.

To dump expired flows to Elasticsearch ntopng requires the -F modifier followed by a string in the following format:

es;<idx type>;<idx name>;<es URL>;<http auth>

The string has 5 semi-colon separated fields

  • es instructs ntopng to dump flows to Elasticsearch
  • <idx type> “_type” to use in exported documents
  • <idx name> index to use for exported documents [ accepts strftime() format ]
  • <es URL> URL of Elasticsearch Bulk API [ ie:]
  • <http auth> Basic HTTP Authentication [ username:password ]




Indexes are like ‘databases’ in a RDBMS terms. An index is a logical namespace which maps to one or more primary shards and can have zero or more replica shards distributed across nodes of a cluster. Index mapping defines the multiple supported types.

Mapping is required for Elasticsearch to correctly interpret all fields produced by ntopng, specifically those containing IP and Geo Location data. This is achieved by using a mapping template for ntop types, automatically inserted by the application at startup. Note this action requires full admin rights on the cluster in order to be performed successfully.

Ntopng will create Indexes and Mapping automatically on startup with no action required. Each time the index name changes, a new Index is created. By default, ntopng creates one daily index (i.e.: ntopng-2015.11.21). Index types can be used to differentiate instances.

Data Rotation:

The official Curator tool from Elastic can be used to manage and rotate Indexes created by ntopng according to the user preferences and requirements.

10.4. Logstash

Logstash is an open source, server-side data processing pipeline that ingests data from a multitude of sources simultaneously, transforms it, and then sends it to a downstream ‘stash’ such as ElasticSearch. Ntopng can connect to a Logstash instance and send monitored flows to that instance.

To dump expired flows to Logstash ntopng requires the -F modifier followed by a string in the following format:


The string has 4 semi-colon separated fields - logstash instructs ntopng to dump flows to Logstash - <host> contains the name or IP address of the host that is running Logstash - <proto> specifies the protocol (e.g., tcp) to be used for the flow export - <port> indicates the port on which the Logstash process is listening



An handy video-tutorial that shows how to send monitored flows to Logstash is available at https://youtu.be/tluAUEeqkCk.