NAME¶

nfcapd - netflow capture daemon

SYNOPSIS¶

nfcapd [options]

DESCRIPTION¶

nfcapd is the netflow capture daemon of the nfdump tools. It reads netflow data from the network and stores it into files. The output file is automatically rotated and renamed every n minutes - typically 5 min - according the timestamp YYYYMMddhhmm of the interval e.g. nfcapd.201907110845 contains the data from July 11th 2019 08:45 onward. If the time interval is smaller then 60s, the naming extends to seconds e.g. nfcapd.20190711084510.

Netflow version v1, v5, v7 and v9 and IPFIX are transparently supported.

Extensions: nfcapd supports a large number of v9 tags. In order to optimise disk space and performance, v9 tags are grouped into a number of extensions which may or may not be stored into the data file. Therefore the v9 templates configured on the exporter may be tuned according the collector. Only those tags common to both are stored into the data files.

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 option templates (tags #34, #35 or #48, #49, #50 ) or in the unofficial v5 header hack. Note: Not all platforms (or IOS/JunOS 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 the default sampling rate given by -s is negative, this will hard overwrite any device specific announced sampling rates.

NSEL/ASA Support: nfcapd can be compiled with NSEL/ASA support included. See notes on NSEL/ASA

NEL (NAT Event logging): nfcapd can be compiled with CISCO NEL support included. See notes on NEL.

OPTIONS¶

-p portnum

Specifies the port number to listen. Default port is 9995

-b bindhost

Specifies the hostname/IPv4/IPv6 address to bind for listening. This can be an IP address or a hostname, resolving to an IP address attached to an interface. Defaults to any available IPv4 interface, if not specified.

-4

Forces nfcapd to listen on IPv4 addresses only. Can be used together with -b if a hostname has an IPv4 and IPv6 address record.

-6

Forces nfcapd to listen on IPv6 addresses only. Can be used together with -b if a hostname has an IPv4 and IPv6 address record. Depending on the socket implementation -6 also accepts IPv4 data.

-J MulticastGroup

Join the specified IPv4 or IPv6 multicast group for listening.

-R host[/port}

Enable packet repeater. Send all incoming packets to another host and port. host is either a valid IPv4/IPv6 address, or a valid symbolic hostname, which resolves to a IPv6 or IPv4 address. port may be omitted and defaults to port 9995. Note: Due to IPv4/IPv6 accepted addresses the port separator is '/'. Up to 8 repeaters my be defined.

-I IdentString ( capital letter i )

Specifies an ident string, which describes the source e.g. the name of the router. This string is put into the stat record to identify the source. Default is 'none'. This is for compatibility with nfdump 1.5.x and used to specify a single netflow source. See -n

-l base_directory ( letter ell )

Specifies the base directory to store the output files. If a sub hierarchy is specified with -S the final directory is concatenated to base_directory/sub_hierarchy. This is for compatibility with nfdump 1.5.x and used to specify a single netflow source. See -n

-n <Ident,IP,base_directory>

Configures a netflow source named Ident and identified by source IP address IP. The base directory for the flow files is base_directory. If a sub hierarchy is specified with -S the final directory is concatenated to base_directory/sub_hierarchy. Multiple netflow sources can be specified. All data is sent to the same port specified by -p. Note: You must not mix -n option with -I and -l. Use either syntax.

-N <file>

Specifies the file to read to add multiple netflow sources. The file is expected to contain one netflow source per line based on the same syntax than the -n option. Comments are not interpreted. Ident collision are not handled if -N is specified multiple times.

-M <dynbase_directory>

Specifies the base directory to store the output files. In contrast to -l -M allows to add dynamically new flow sources (exporters), as they appear. All exporters send netflow data to the same port and IP. For each dynamically added source, a new directory is created with the name of the IPv4/IPv6 address of the exporter. All '.' and ':" in IP addresses are replaced be '-' e.g. 10.11.12.13 is converted to the directory name 10-11-12-13. Note: Please make sure to restrict at host level the potential range of IP addresses which are allowed to connect to nfcapd. Otherwise you risk a potential DoS attack on nfcapd, as nfcapd has no built in restrictions.

-f <pcap_file>

Read netflow packets from a give pcap_file instead of the network. This requires nfcapd to be compiled with the pcap option and is intended for debugging only.

-s <rate>

Apply default sampling rate rate to all netflow records, unless the sampling rate is announced by the exporting device. In that case the announced sampling rate is applied. If <rate> is negative, this will hard overwrite any device specific announced sampling rates.

-S <num>

Allows to specify an additional directory sub hierarchy to store the data files. The default is 0, no sub hierarchy, which means the files go directly in the base directory (-l). The base directory (-l) is concatenated with the specified sub hierarchy format to form the final data directory. The following hierarchies are defined:

-T <extension list>

The argument is considered legacy. By default all matching extension sent by the exporter are stored. You still may overwrite this, if you want to skip certain extansions. Regardless of the extension list, the following netflow data is stored per record: first, last, fwd status, tcp flags, proto, (src)tos, src port, dst port, src ipaddr, dst ipaddr, in(packets), in(bytes). In addition nfcapd recognises the extensions as described below. Some are valid for v5/v7/v9, but most of them make only sense for v9. Any specified extensions which do not exist in the input netflow records are ignored.

Extensions:

-t interval

Specifies the time interval in seconds to rotate files. The default value is 300s ( 5min ). The smallest interval is 2s.

-w

Align file rotation with next n minute ( specified by -t ) interval. Example: If interval is 5 min, sync at 0,5,10... wall clock minutes Default: no alignment.

-x cmd

Run command cmd at the end of every interval, when a new file becomes available. The following command expansion is available:

-X

Collect and embed extended statistics. Currently a port and bpp histogram is embedded. Mostly experimental for now

-e

Auto expire files at every cycle. max lifetime and max filesize are defined using nfexpire(1)

-P pidfile

Specify name of pidfile. Default is no pidfile.

-D

Daemon mode: fork to background and detach from terminal. Nfcapd terminates on signal TERM, INT and HUP.

-u userid

Change to the user userid as soon as possible. Only root is allowed to use this option.

-g groupid

Change to the group groupid as soon as possible. Only root is allowed use this option.

-B bufflen

Specifies the socket input buffer length in bytes. For high volume traffic ( near GB traffic ) it is recommended to set this value as high as possible ( typically > 100k ), otherwise you risk to lose packets. The default is OS ( and kernel ) dependent.

-E

Print netflow records in nfdump raw format to stdout. This option is for debugging purpose only, to see how incoming netflow data is processed and stored.

-j

Compress flows. Use bz2 compression in output file. Note: not recommended while collecting

-y

Compress flows. Use LZ4 compression in output file.

-z

Compress flows. Use fast LZO1X-1 compression in output file.

-V

Print nfcapd version and exit.

-h

Print help text to stdout with all options and exit.

RETURN VALUE¶

Returns 0 on success, or 255 if initialization failed.

LOGGING¶

nfcapd logs to syslog with SYSLOG_FACILITY LOG_DAEMON For normal operation level 'warning' should be fine. More information is reported at level 'info' and 'debug'.

A small statistic about the collected flows, as well as errors are reported at the end of every interval to syslog with level 'info'.

EXAMPLES¶

All flows are sent to port 9995 from all exporters and stored into a single file. All known v9 tags are taken.

All flows from 2 different exporters are sent to port 8877 and stored in separate directory trees. All known v9 tags are taken. Input buffer size is set to 128000 bytes

Only accept from from a single exporter and only extension 3,4 and 5 are accepted. Run a given command when files are rotated and automatically expire flows:

NOTES¶

Multiple netflow sources:

Netflow data may be sent from different exporters to a single nfcapd process. Use the -n option to separate each netflow source to a different data directory. For compatibility with nfdump 1.5.x, old style -l/-I options are still valid. In that case all flows from all sources are stored in a single file. For high volume netflow streams, it is still recommended to have a single nfcapd process per netflow source.

Nfdump supports a large number of v9 and ipfix elements. For a detailed list chek the netflow_v9 and ipfix header files. 32 and 64 bit are supported for all counters. 32it AS numbers are supported.

The format of the data files is netflow version independent.

Socket buffer: Setting the socket buffer size is system dependent. When starting up, nfcapd returns the number of bytes the buffer was actually set. This is done by reading back the buffer size and may differ from what you requested.

SEE ALSO¶

nfdump(1), nfprofile(1), nfreplay(1)

BUGS¶

No software without bugs! Please report any bugs back to me.