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

Introduction

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:

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, AS information and TOR exit node information. AS information is enriched only, if it is not available in the original flow record. 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 <u>geolooup</u>(1) man page for more details. IP adresses can be tagged as TOR exit nodes, from the optional torDB database, created by the torlookup program. Please chaeck the <u>torlookup</u>(1) man page for details.

There is also a go-nfdump module to read nfdump flows files in Golang.

Compatibility

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.

If you have lots of flows files from nfdump-1.6.x, it is recommended to convert these to the new format. You can convert any old files from nfdump-1.6.x to nfdump-1.7 format by reading/writing files: ./nfdump -r old-flowfile -y -w new-flowfile

Please note, that only nfdump may read nfdump-1.6.x flow files. All other programs understand the new file format only.

Note for NfSen users: If you use NfSen, you must upgrade NfSen to the latest Github version https://github.com/phaag/nfsen. All specific binaries such as nfprofile and nftrack are still available with nfdump-1.7 but may be removed in future.

Improvements

Additional programs

The nfdump program suite also contains 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. ( ex: src geo US ). 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 paid 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

The nfdump program suite also contains torlookup. It allows either to enrich IP addresses by a TOR exit flag. Flows may be filtered according to TOR IP addresses ( ex: src ip tor ). torlookup may also be used as standalone program to lookup IPs for TOR exit node intervals with as many requests as you have. In order to use torlookup or the nfdump output enrichment , you need to create the tordb first. See also the toorlookup(1) man page. torlookup needs to be enabled when running configure: --enable-tor

NSEL/ASA, NEL/NAT support

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

Installation

Building and config options

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

For various older Linuxes need a more modern compiler:

CentOS 7.x:

% 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

Ubuntu 18.04 LTS:

% sudo apt-get install clang-10
% CC=clang-10 ./configure ...

The following config options are available: ( see ./configure --help for the complete list)

Development and beta options

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 compatible files. "sfcapd includes sFlow(TM) code, freely available from https://github.com/sflow/sflowtool.

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 compatible files or sends the flows to a remote nfcapd collector. It is nfcapd's companion to convert traffic directly into nfdump records. Nfpcap can optionally integrate lots of meta data as well as prt of the payload. ( -o fat, payload)

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 note: You need a legitimate Maxmind account (free or paid) in order to download the files.

torlookup - TOR location lookup program. torlookup converts tor information 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 flag tor exit node IPs.

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.

Compression

Binary data files can optionally be compressed by using either LZO1X-1, LZ4, ZSTD or bzip2 compression LZO is fastest but less efficient, LZ4 and ZSTD are fast and pretty efficient and bzip2 is slow but efficient.

By default LZO and LZ4 embedded without external dependancies. Bzip2 and ZSTD are optional libraries, which are automatically added, if they are found while configuring and compiling.

The standard configure process checks for the installed libraries lz4, bz2 and zstd and enables them if they are found. configure understands the following options:

  --with-lz4path=PATH     Expect liblz4 installed in PATH; default /usr/local
  --with-zstdpath=PATH    Expect libzstd installed in PATH; default /usr/local
  --with-bz2path=PATH     Expect libbz2 installed in PATH; default /usr/local

If no option is given and no library is found that compression algorithm is disabled. For LZ4, if no library is found, the embedded version is used. Compression algorithms can also be explicitly disabled by setting with-xxxpath=no In the case of lz4, it disables the system installed version and uses the embedded one.

Recommendation

If you compress automatically flows while they are collected, use LZ4 -z=lz4 as a standard.

Notes: 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 <algo[:level]>. You may also apply compression levels to lz4 and zstd such as -z=zstd:9 or -z=lz4:5 to improve efficiency at the cose of more CPU and slower compression speed.

For more details on each methde, see:

LZO1X-1: http://www.oberhumer.com/opensource/lzo

LZ4: https://github.com/lz4/lz4

ZSTD: https://github.com/facebook/zstd

bzip2: http://www.bzip.org

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

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:

/flow_base_dir/router1
/flow_base_dir/router2

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 router1,172.16.17.18,/flow_base_dir/router1 \
	-n router2,172.16.17.20,/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 peter@people.ops-trust.net

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 192.168.92.162 255.255.255.224
 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 192.168.92.218 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 192.168.92.162 255.255.255.224
 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 192.168.92.218 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 and infix: nfcapd supports a large range of netflow v9 and ipfix tags. Version 1.7 of nfdump also supports FNF - flexible netflow, subtemplates and understands a few specific exporters such as yaf.

sfcpad

This collector collects sflow https://www.sflow.org exports. It is largely identical to nfcapd except it only understands sflow packets.

nfpcapd

This collector is able to listen on a host interface and generates netflow data from the network data stream on that interface. It make use of PACKET_RX_RING to read packets on an interface device level (TPACKETV3) on Linux hosts or of the BPF interface - Berkeley Packet Filter on *BSD hosts which provides raw access to data link layers. Nfpcapd builds an internal netflow cache which is periodically written to disk or forwarded to an nfcapd server. As a special feature, nfpcpad may collect the first few bytes of a network connection, if requested to do so ( -o payload), which allows filter and evaluate the flows with nfdump later.

Listen on eth0 and store the flows locally. Set flow cache active timeout to 60s, inactive tiemout to 30s:

nfpcapd -D -S 2 -w /var/flows -i eth0 -e 60,30 -u daemon -g daemon

Listen on eth0 and forward flow data to nfcapd running on a remote host. Add tunnel infos, MAC addr, vlan labels and first packet payload to the flows:

nfpcapd -D -S 2 -H 192.168.168.40 -i eth0 -e 60,30 -o fat,payload -u daemon -g daemon

In order to evaluate the payload, nfdump has some simple payload decoders for DNS, ja3, ja3s, ja4 and a few other.

Alternatively nfpcapd can also convert existing cap files into flow data:

nfpcapd -S 2 -w /var/flows -r pcapfile.pcap -e 60,30 -o fat,payload

Flowset record types

Links

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

Sampling

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/ipfix option templates with tags set (#302, #304, #305, #306), ( #48, #49, #50 ), ( #34, #35)or in the unofficial v5 header hack. The sampling data is stored in the sampling PacketInterval/PacketSpace model. If announced differently, it is converted accordingly.

Note: Not all platforms (or vendor software 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)

If you like this project your company may consider sponsoring it :) https://github.com/sponsors/phaag