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nfdump-1.7.x or nfdump unicorn is the new release of nfdump.

nfdump-1.6.x receives bug fixes, but will no longer get new features. The latest release for nfdump-1.6.x is nfdump-1.6.25.


nfdump is a toolset in order to collect and process netflow/ipfix and sflow data, sent from netflow/sflow compatible devices.

The toolset contains several collectors to collect flow data:

  • nfcapd supports netflow v1, v5/v7, v9 and IPFIX
  • sfcapd supports sflow.
  • nfpcapd converts pcap data read from a host interface or from pcap files.

The collected flow data is stored into files and can be process afterwards. nfdump processes and lists the flows in many different output formats and can create a wide range of statistics.

nfdump has a very powerful flow filter to process flows. The filter syn‐ tax is very similar to tcpdump, but adapted and extended for flow filter‐ ing. A flow filter may also contain arrays of many thousand IP addresses etc. to search for specific records.

nfdump can aggreagte flows according to a user defined number of ele‐ ments. This masks certain elements and allows to sum up flow records matching the same values.

The combination of flow filtering and aggregation as input for any flow statistics allows complex flow processing. Pre‐filtered and aggregated flow data may also be written back into a binary flow file, which again may be processed with nfdump

nfdump can enrich the listing of flows with geo location information and AS information, unless AS information is already available in the flow records. IP addresses can be tagged with a two letter country code, or with a longer location label containing the geographic region, country and city. The geo location and AS information is retrieved from the optional geoDB database, created by the geolookup program from the nfdump tools. geolookup uses the Maxmind database GeoDB or GeoLite2 to create a binary lookup database for nfdump Please check the geolooup(1) man page for more details.


You may use nfdump-1.6.24 oder nfdump-1.7.x, depending on your needs. nfdump-1.7.x is compatible to nfdump-1.6.18, which means it can read files created with nfdump-1.6.18 or newer. Flow files created with earlier nfdump versions may not contain all flow elements. If you have older files, it is recommended to use nfdump-1.6.17 to update the records.

Nfdump 1.7.x provides the same set of programs as 1.6.x and can be used almost as a drop-in replacement. This may change in future and older legacy programs may be removed. You can convert any old files from nfdump-1.6 to nfdump-1.7 format by reading/writing files: ./nfdump -r old-flowfile -y -w new-flowfile

Please note, that only nfdump may read older flow files. All other programs relay on the new file format.

Although nfdump-1.7.x ist mostly compatible with old Nfsen, it not recommended to replace nfdump iin your NfSen installation. However, all specific binaries such as nfprofile and nftrack are still available with nfdump-1.7 but may be removed in future.


  • nfdump is now a multi-threaded program and uses parallel threads mainly for reading, writing and processing flows as well as for sorting. This may result in faster flow processing, depending on the tasks. The speedimprovement also heavily depends on the hardware (SSD/HD) and flow compression option.

  • For netflow v9 and IPFIX, nfdump now supports flexible length fields. This improves compatibility with some exporters such as yaf and others.

  • Support for Cisco Network Based Application Recognition (NBAR).

  • Supports Maxmind geo location information to tag/geolocate IP addresses and AS numbers.

  • nfpcapd automatically uses TPACKET_V3 for Linux or direct BPF sockets for *BSD. This improves packet processing. It adds new options to collect MAC and VLAN information if requested as well as the payload of the first packet. This creates a lot of new possibilities in oder to process and filter flows, such as nfdump -r flowfile 'payload content "POST"' nfpcapd can now store flow files locally or can sent them to a remote nfcapd collector.

  • Metric exports: By default, every 60s a flow summary statistics can be sent to a UNIX socket. The corresponding program may be nfinflux to insert these metrics into an influxDB or nfexporter for Prometheus monitoring.

New programs

The nfdump program suite has been extended by geolookup. It allows either to enrich IP addresses by country codes/locations and may add potential missing AS information. Flows may be filtered according to country codes. geolookup may also be used as standalone program to lookup IPs for AS/Geo information, similar to the famous Team Cymru whois service. geolookup uses a local database, which allows to process as many requests as you have. In order to use geolookup, you need either a free or payed Maxmind account in order to convert the Maxmind .csv files into an nfdump vector data file. geolookup needs to be enabled when running configure: --enable-maxmind


NSEL (Network Event Security Logging) as well as NEL (NAT Event Logging) are technologies invented by CISCO and also use the netflow v9 protocol. However, NSEL and NEL are not flows as commonly known but rather Events! exported from specific devices such as CISCO ASA. nfdump supports Event looging as part of netflow v9.

Jun OS NAT Event Logging is mostly compatible with CISCO's NAT Event Logging - mostly - it needs another data interpretation. See --enable-jnat below


Building and config options

The toolset is build upon the autotools framework. Run ./ first. Afterwards ./configure make and make install should do the trick.

If you run CentOS 7.x you need to install a more recent compiler:

yum install centos-release-scl

Then you can install GCC 8 and its C++ compiler:

yum install devtoolset-8-gcc devtoolset-8-gcc-c++

To switch to a shell which defaults gcc and g++ to this GCC version, use:

scl enable devtoolset-8 -- bash

The following config options are available:

  • --enable-sflow
    Build sflow collector sfcapd; default is NO
  • --enable-nfpcapd
    Build nfpcapd collector to create netflow data from interface traffic or precollected pcap traffic; default is NO
  • --enable-maxmind
    Build geolookup program; default is NO
  • --enable-nsel
    Compile nfdump, to read and process NSEL/NEL event data; default is NO
  • --enable-jnat
    compile nfdump, to read and process JunOS NAT event logging NO
  • --enable-ftconv
    Build the flow-tools to nfdump converter; default is NO
  • --enable-nfprofile
    Build nfprofile used by NfSen; default is NO
  • --enable-nftrack
    Build nftrack used by PortTracker; default is NO

Development and beta options

  • --enable-devel
    Insert lots of debug and development code into nfdump for testing and debugging; default is NO
  • --enable-readpcap
    Add code to nfcapd to read flow data also from pcap files; default is NO

The tools

nfcapd - netflow collector daemon.
Collects the netflow data, sent from exporters and stores the flow records into files. Automatically rotates files every n minutes. ( typically every 5 min ) The netflow versions mentioned above are read transparently Multiple netflow streams can be collected by a single or collector.
nfcapd can listen on IPv6 or IPv4. Furthermore multicast is supported.

nfdump - process collected netflow records.
Nfdump reads the netflow data from one or many files stored by nfcapd. It's filter syntax is similar to tcpdump ( pcap like ) but adapted for netflow. If you like tcpdump you will like nfdump. nfdump displays netflow data and/or creates top N statistics of flows, bytes, packets. nfdump has a powerful and flexible flow aggregation including bi-directional flows. The output format is user selectable and also includes a simple csv format for post processing.

nfanon - anonymize netflow records
IP addresses in flow records are anonimized using the CryptoPAn method.

nfexpire - expire old netflow data
Manages data expiration. Sets appropriate limits. Used by NfSen.

nfreplay - netflow replay
Reads the netflow data from the files stored by nfcapd and sends it over the network to another host.

Optional binaries:

sfcapd - sflow collector daemon
scfapd collects sflow data and stores it into nfcapd comaptible files. "sfcapd includes sFlow(TM) code, freely available from

nfpcapd - pcap to netflow collector daemon
nfpcapd listens on a network interface, or reads precollected pcap traffic. It either stores locally flow records into nfcapd comaptible files or sends the flows to a remote nfcapd collector. It is nfcapd's companion to convert traffic directly into nfdump records.

geolookup - Geo location lookup program. geolookup converts Maxmind's .csv files into the nfdump vector DB. The converted DB may be used as a standalone lookup tool, or be be used by nfdump in order to automatically lookup country and location. Please not: You need a legitimate Maxmind account (free or payed) in order to download the files.

ft2nfdump - flow-tools flow converter
ft2nfdump converts flow-tools data into nfdump format.

nfprofile - netflow profiler. Required by NfSen
Reads the netflow data from the files stored by nfcapd. Filters the netflow data according to the specified filter sets ( profiles ) and stores the filtered data into files for later use.

nftrack - Port tracking decoder for NfSen plugin PortTracker.

nfreader - Framework for programmers
nfreader is a framework to read nfdump files for any other purpose. Own C code can be added to process flows. nfreader is not installed

Notes for sflow users:

sfcapd and nfcapd can be used concurrently to collect netflow and sflow data at the same time. Generic command line options apply to both collectors likewise. sfcapd's sflow decoding module is based on InMon's sflowtool code and supports similar fields as nfcapd does for netflow v9, which is a subset of all available sflow fields in an sflow record. More fields may be integrated in future versions of sfcapd.


Binary data files can optionally be compressed using either the fast LZO1X-1 compression, LZ4 or the efficient but slow bzip2 method. If you compress automatically flows while they are collected, LZO1X-1 or LZ4 methods are recommended. bzip2 uses about 30 times more CPU than LZO1X-1. Use bzip2 to archive netflow data, which may reduce the disk usage again by a factor of 2. The compression of flow files can be changed any time with nfdump -J For more details on each methde, see:




You can check the compression speed for your system by running ./nftest <path/to/an/existing/netflow/file>.

General Operation of nfdump

The goal of the design is to able to analyze netflow data from the past as well as to track interesting traffic patterns continuously. The amount of time back in the past is limited only by the disk storage available for all the netflow data. The tools are optimized for speed for efficient filtering. The filter rules should look familiar to the syntax of tcpdump ( pcap compatible ).

All data is stored to disk, before it gets analyzed. This separates the process of storing and analyzing the data.

The data is organized in a time-based fashion. Every n minutes

  • typically 5 min - nfcapd rotates and renames the output file with the timestamp nfcapd.YYYYMMddhhmm of the interval e.g. nfcapd.200907110845 contains data from July 11th 2009 08:45 onward. Based on a 5min time interval, this results in 288 files per day.

Analyzing the data can be done for a single file, or by concatenating several files for a single output. The output is either ASCII text or binary data, when saved into a file, ready to be processed again with the same tools.

You may have several netflow sources - let's say 'router1' 'router2' and so on. The data is organized as follows:


which means router1 and router2 are subdirs of the flow_base_dir.

Although several flow sources can be sent to a single collector, It's recommended to have multiple collector on busy networks for each source. Example: Start two collectors on different ports:

nfcapd -D -S 2 -B 1024000 -w /flow_base_dir/router1 -p 23456
nfcapd -D -S 2 -B 1024000 -w /flow_base_dir/router2 -p 23457

nfcapd can handle multiple flow sources. All sources can go into a single file or can be split:

All into the same file:

nfcapd -D -S 2 -w /flow_base_dir/routers -p 23456

Collected on one port and split per source:

nfcapd -D -S 2 -n router1,,/flow_base_dir/router1 \
	-n router2,,/flow_base_dir/router2 -p 23456

See nfcapd(1) for a detailed explanation of all options.

Security: none of the tools requires root privileges, unless you have a port < 1024. However, there is no access control mechanism in nfcapd. It is assumed, that host level security is in place to filter the proper IP addresses.

See the manual pages or use the -h switch for details on using each of the programs. For any questions send email to

Configure your router to export netflow. See the relevant documentation for your model.

A generic Cisco sample configuration enabling NetFlow on an interface:

ip address
 interface fastethernet 0/0
 ip route-cache flow

To tell the router where to send the NetFlow data, enter the following global configuration command:

ip flow-export 9995
ip flow-export version 5 

ip flow-cache timeout active 5

This breaks up long-lived flows into 5-minute segments. You can choose any number of minutes between 1 and 60;

Netflow v9 full export example of a cisco 7200 with sampling enabled:

interface Ethernet1/0
 ip address
 duplex half
 flow-sampler my-map
flow-sampler-map my-map
 mode random one-out-of 5
ip flow-cache timeout inactive 60
ip flow-cache timeout active 1
ip flow-capture fragment-offset
ip flow-capture packet-length
ip flow-capture ttl
ip flow-capture vlan-id
ip flow-capture icmp
ip flow-capture ip-id
ip flow-capture mac-addresses
ip flow-export version 9
ip flow-export template options export-stats
ip flow-export template options sampler
ip flow-export template options timeout-rate 1
ip flow-export template timeout-rate 1
ip flow-export destination 9995

See the relevant documentation for a full description of netflow commands

Note: Netflow version v5 and v7 have 32 bit counter values. The number of packets or bytes may overflow this value, within the flow-cache timeout on very busy routers. To prevent overflow, you may consider to reduce the flow-cache timeout to lower values. All nfdump tools use 64 bit counters internally, which means, all aggregated values are correctly reported.

The binary format of the data files is netflow version independent. For speed reasons the binary format is machine architecture dependent, and as such can not be exchanged between little and big endian systems. Internally nfdump does all processing IP protocol independent, which means everything works for IPv4 as well as IPv6 addresses. See the nfdump(1) man page for details.

netflow version 9: nfcapd supports a large range of netflow v9 tags. Version 1.6 nfdump supports the following fields. This list can be found in netflow_v9.h

Flowset record types


Extensions: nfcapd supports a large number of v9 tags. It automatically add extensions to store data for v9/IPFIX elements which are supported.


By default, the sampling rate is set to 1 (unsampled) or to any given value specified by the -s cmd line option. If sampling information is found in the netflow stream, it overwrites the default value. Sampling is automatically recognised when announced in v9 option templates (tags #48, #49, #50 ), (tag #34, #35) or in the unofficial v5 header hack. Note: Not all platforms (or CISCO IOS versions) support exporting sampling information in netflow data, even if sampling is configured. The number of bytes/packets in each netflow record is automatically multiplied by the sampling rate. The total number of flows is not changed as this is not accurate enough. (Small flows versus large flows)

For more information, see the GitHub Wiki.