-i <dev|pcap|->, -d <dev|pcap|->, --in <dev|pcap|->, --dev
<dev|pcap|->
Defines an input device. This can either be a networking
device, a pcap file or stdin ('-'). In case of a pcap
file, the pcap type (-D option) is determined
automatically by the pcap file magic. In case of stdin, it
is assumed that the input stream is a pcap file. If the
pcap link type is Netlink and pcap type is default format
(usec or nsec), then each packet will be wrapped with pcap
cooked header [2].
-o <dev|pcap|dir|cfg|->, --out <dev|pcap|dir|cfg|->
Defines the output device. This can either be a networking
device, a pcap file, a folder, a trafgen(8) configuration
file or stdout ('-'). If the output device is a pcap or
trafgen(8) configuration file, it may include a time
format as defined by strfime(3). If used in conjunction
with the -F option, each rotated file will have a unique
time stamp. In the case of a pcap file that should not
have the default pcap type (0xa1b2c3d4), the additional
option -T must be provided. If a directory is given, then,
instead of a single pcap file, multiple pcap files are
generated with rotation based on maximum file size or a
given interval (-F option). Optionally, sending the SIGHUP
signal to the netsniff-ng process causes a premature
rotation of the file. A trafgen configuration file can
currently only be specified if the input device is a pcap
file. To specify a pcap file as the output device, the
file name must have '.pcap' as its extension. If stdout is
given as a device, then a trafgen configuration will be
written to stdout if the input device is a pcap file, or a
pcap file if the input device is a networking device. If
the input device is a Netlink monitor device and pcap type
is default (usec or nsec) then each packet will be wrapped
with pcap cooked header [2] to keep Netlink family number
(Kuznetzov's and netsniff-ng pcap types already contain
family number in protocol number field).
-C <id>, --fanout-group <id>
If multiple netsniff-ng instances are being started that
all have the same packet fanout group id, then the ingress
network traffic being captured is being distributed/load-
balanced among these group participants. This gives a much
better scaling than running multiple netsniff-ng processes
without a fanout group parameter in parallel, but only
with a BPF filter attached as a packet would otherwise
need to be delivered to all such capturing processes,
instead of only once to such a fanout member. Naturally,
each fanout member can have its own BPF filters attached.
-K <hash|lb|cpu|rnd|roll|qm>, --fanout-type
<hash|lb|cpu|rnd|roll|qm>
This parameter specifies the fanout discipline, in other
words, how the captured network traffic is dispatched to
the fanout group members. Options are to distribute
traffic by the packet hash ('hash'), in a round-robin
manner ('lb'), by CPU the packet arrived on ('cpu'), by
random ('rnd'), by rolling over sockets ('roll') which
means if one socket's queue is full, we move on to the
next one, or by NIC hardware queue mapping ('qm').
-L <defrag|roll>, --fanout-opts <defrag|roll>
Defines some auxiliary fanout options to be used in
addition to a given fanout type. These options apply to
any fanout type. In case of 'defrag', the kernel is being
told to defragment packets before delivering to user
space, and 'roll' provides the same roll-over option as
the 'roll' fanout type, so that on any different fanout
type being used (e.g. 'qm') the socket may temporarily
roll over to the next fanout group member in case the
original one's queue is full.
-f, --filter <bpf-file|-|expr>
Specifies to not dump all traffic, but to filter the
network packet haystack. As a filter, either a bpfc(8)
compiled file/stdin can be passed as a parameter or a
tcpdump(1)-like filter expression in quotes. For details
regarding the bpf-file have a look at bpfc(8), for details
regarding a tcpdump(1)-like filter have a look at section
'filter example' or at pcap-filter(7). A filter
expression may also be passed to netsniff-ng without
option -f in case there is no subsequent option following
after the command-line filter expression.
-t, --type <type>
This defines some sort of filtering mechanisms in terms of
addressing. Possible values for type are 'host' (to us),
'broadcast' (to all), 'multicast' (to group), 'others'
(promiscuous mode) or 'outgoing' (from us).
-F, --interval <size|time>
If the output device is a folder, with '-F', it is
possible to define the pcap file rotation interval either
in terms of size or time. Thus, when the interval limit
has been reached, a new pcap file will be started. As size
parameter, the following values are accepted
'<num>KiB/MiB/GiB'; As time parameter, it can be
'<num>s/sec/min/hrs'.
-J, --jumbo-support
By default, in pcap replay or redirect mode, netsniff-ng's
ring buffer frames are a fixed size of 2048 bytes. This
means that if you are expecting jumbo frames or even super
jumbo frames to pass through your network, then you need
to enable support for that by using this option. However,
this has the disadvantage of performance degradation and a
bigger memory footprint for the ring buffer. Note that
this doesn't affect (pcap) capturing mode, since tpacket
in version 3 is used!
-R, --rfraw
In case the input or output networking device is a
wireless device, it is possible with netsniff-ng to turn
this into monitor mode and create a mon<X> device that
netsniff-ng will be listening on instead of wlan<X>, for
instance. This enables netsniff-ng to analyze, dump, or
even replay raw 802.11 frames.
-n <0|uint>, --num <0|uint>
Process a number of packets and then exit. If the number
of packets is 0, then this is equivalent to infinite
packets resp. processing until interrupted. Otherwise, a
number given as an unsigned integer will limit processing.
-O <N>, --overwrite <N>
A number from 0 to N-1 will be used in the file name
instead of a Unix timestamp. The previous file will be
overwritten when number wraps around. The maximum value is
2^32 - 1. Intended for rotating capture files when used
with options -F and -P.
-P <name>, --prefix <name>
When dumping pcap files into a folder, a file name prefix
can be defined with this option. If not otherwise
specified, the default prefix is 'dump-' followed by a
Unix timestamp. Use '--prefex ""' to set filename as
seconds since the Unix Epoch e.g. 1369179203.pcap
-T <pcap-magic>, --magic <pcap-magic>
Specify a pcap type for storage. Different pcap types with
their various meta data capabilities are shown with option
-D. If not otherwise specified, the pcap-magic 0xa1b2c3d4,
also known as a standard tcpdump-capable pcap format, is
used. Pcap files with swapped endianness are also
supported.
-D, --dump-pcap-types
Dump all available pcap types with their capabilities and
magic numbers that can be used with option '-T' to stdout
and exit.
-B, --dump-bpf
If a Berkeley Packet Filter is given, for example via
option '-f', then dump the BPF disassembly to stdout
during ring setup. This only serves for informative or
verification purposes.
-r, --rand
If the input and output device are both networking
devices, then this option will randomize packet order in
the output ring buffer.
-M, --no-promisc
The networking interface will not be put into promiscuous
mode. By default, promiscuous mode is turned on.
-N, --no-hwtimestamp
Disable taking hardware time stamps for RX packets. By
default, if the network device supports hardware time
stamping, the hardware time stamps will be used when
writing packets to pcap files. This option disables this
behavior and forces (kernel based) software time stamps to
be used, even if hardware time stamps are available.
-A, --no-sock-mem
On startup and shutdown, netsniff-ng tries to increase
socket read and write buffers if appropriate. This option
will prevent netsniff-ng from doing so.
-m, --mmap
Use mmap(2) as pcap file I/O. This is the default when
replaying pcap files.
-G, --sg
Use scatter-gather as pcap file I/O. This is the default
when capturing pcap files.
-c, --clrw
Use slower read(2) and write(2) I/O. This is not the
default case anywhere, but in some situations it could be
preferred as it has a lower latency on write-back to disc.
-S <size>, --ring-size <size>
Manually define the RX_RING resp. TX_RING size in
'<num>KiB/MiB/GiB'. By default, the size is determined
based on the network connectivity rate.
-k <uint>, --kernel-pull <uint>
Manually define the interval in micro-seconds where the
kernel should be triggered to batch process the ring
buffer frames. By default, it is every 10us, but it can
manually be prolonged, for instance.
-b <cpu>, --bind-cpu <cpu>
Pin netsniff-ng to a specific CPU and also pin resp.
migrate the NIC's IRQ CPU affinity to this CPU. This
option should be preferred in combination with -s in case
a middle to high packet rate is expected.
-u <uid>, --user <uid> resp. -g <gid>, --group <gid>
After ring setup drop privileges to a non-root user/group
combination.
-H, --prio-high
Set this process as a high priority process in order to
achieve a higher scheduling rate resp. CPU time. This is
however not the default setting, since it could lead to
starvation of other processes, for example low priority
kernel threads.
-Q, --notouch-irq
Do not reassign the NIC's IRQ CPU affinity settings.
-s, --silent
Do not enter the packet dissector at all and do not print
any packet information to the terminal. Just shut up and
be silent. This option should be preferred in combination
with pcap recording or replay, since it will not flood
your terminal which causes a significant performance
degradation.
-q, --less
Print a less verbose one-line information for each packet
to the terminal.
-X, --hex
Only dump packets in hex format to the terminal.
-l, --ascii
Only display ASCII printable characters.
-U, --update
If geographical IP location is used, the built-in database
update mechanism will be invoked to get Maxmind's latest
database. To configure search locations for databases, the
file /etc/netsniff-ng/geoip.conf contains possible
addresses. Thus, to save bandwidth or for mirroring of
Maxmind's databases (to bypass their traffic limit
policy), different hosts or IP addresses can be placed
into geoip.conf, separated by a newline.
-w, --cooked
Replace each frame link header with Linux "cooked" header
[3] which keeps info about link type and protocol. It
allows to dump and dissect frames captured from different
link types when -i "any" was specified, for example.
-V, --verbose
Be more verbose during startup i.e. show detailed ring
setup information.
-v, --version
Show version information and exit.
-h, --help
Show user help and exit.
