Provided by: netsniff-ng_0.6.8-3_amd64 
NAME
netsniff-ng - the packet sniffing beast
SYNOPSIS
netsniff-ng { [options] [filter-expression] }
DESCRIPTION
netsniff-ng is a fast, minimal tool to analyze network packets, capture pcap files, replay
pcap files, and redirect traffic between interfaces with the help of zero-copy packet(7)
sockets. netsniff-ng uses both Linux specific RX_RING and TX_RING interfaces to perform
zero-copy. This is to avoid copy and system call overhead between kernel and user address
space. When we started working on netsniff-ng, the pcap(3) library did not use this zero-
copy facility.
netsniff-ng is Linux specific, meaning there is no support for other operating systems.
Therefore we can keep the code footprint quite minimal and to the point. Linux packet(7)
sockets and its RX_RING and TX_RING interfaces bypass the normal packet processing path
through the networking stack. This is the fastest capturing or transmission performance
one can get from user space out of the box, without having to load unsupported or non-
mainline third-party kernel modules. We explicitly refuse to build netsniff-ng on top of
ntop/PF_RING. Not because we do not like it (we do find it interesting), but because of
the fact that it is not part of the mainline kernel. Therefore, the ntop project has to
maintain and sync out-of-tree drivers to adapt them to their DNA. Eventually, we went for
untainted Linux kernel, since its code has a higher rate of review, maintenance, security
and bug fixes.
netsniff-ng also supports early packet filtering in the kernel. It has support for low-
level and high-level packet filters that are translated into Berkeley Packet Filter
instructions.
netsniff-ng can capture pcap files in several different pcap formats that are
interoperable with other tools. The following pcap I/O methods are supported for efficient
to-disc capturing: scatter-gather, mmap(2), read(2), and write(2). netsniff-ng is also
able to rotate pcap files based on data size or time intervals, thus, making it a useful
backend tool for subsequent traffic analysis.
netsniff-ng itself also supports analysis, replaying, and dumping of raw 802.11 frames.
For online or offline analysis, netsniff-ng has a built-in packet dissector for the
current 802.3 (Ethernet), 802.11* (WLAN), ARP, MPLS, 802.1Q (VLAN), 802.1QinQ, LLDP, IPv4,
IPv6, ICMPv4, ICMPv6, IGMP, TCP and UDP, including GeoIP location analysis. Since
netsniff-ng does not establish any state or perform reassembly during packet dissection,
its memory footprint is quite low, thus, making netsniff-ng quite efficient for offline
analysis of large pcap files as well.
Note that netsniff-ng is currently not multithreaded. However, this does not prevent you
from starting multiple netsniff-ng instances that are pinned to different, non-overlapping
CPUs and f.e. have different BPF filters attached. Likely that at some point in time your
harddisc might become a bottleneck assuming you do not rotate such pcaps in ram (and from
there periodically scheduled move to slower medias). You can then use mergecap(1) to
transform all pcap files into a single large pcap file. Thus, netsniff-ng then works
multithreaded eventually.
netsniff-ng can also be used to debug netlink traffic.
OPTIONS
-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.
USAGE EXAMPLE
netsniff-ng
The most simple command is to just run “netsniff-ng”. This will start listening on
all available networking devices in promiscuous mode and dump the packet dissector
output to the terminal. No files will be recorded.
netsniff-ng --in eth0 --out dump.pcap -s -T 0xa1e2cb12 -b 0 tcp or udp
Capture TCP or UDP traffic from the networking device eth0 into the pcap file named
dump.pcap, which has netsniff-ng specific pcap extensions (see “netsniff-ng -D” for
capabilities). Also, do not print the content to the terminal and pin the process
and NIC IRQ affinity to CPU 0. The pcap write method is scatter-gather I/O.
netsniff-ng --in wlan0 --rfraw --out dump.pcap --silent --bind-cpu 0
Put the wlan0 device into monitoring mode and capture all raw 802.11 frames into
the file dump.pcap. Do not dissect and print the content to the terminal and pin
the process and NIC IRQ affinity to CPU 0. The pcap write method is scatter-gather
I/O.
netsniff-ng --in dump.pcap --mmap --out eth0 -k1000 --silent --bind-cpu 0
Replay the pcap file dump.pcap which is read through mmap(2) I/O and send the
packets out via the eth0 networking device. Do not dissect and print the content to
the terminal and pin the process and NIC IRQ affinity to CPU 0. Also, trigger the
kernel every 1000us to traverse the TX_RING instead of every 10us. Note that the
pcap magic type is detected automatically from the pcap file header.
netsniff-ng --in eth0 --out eth1 --silent --bind-cpu 0 --type host -r
Redirect network traffic from the networking device eth0 to eth1 for traffic that
is destined for our host, thus ignore broadcast, multicast and promiscuous traffic.
Randomize the order of packets for the outgoing device and do not print any packet
contents to the terminal. Also, pin the process and NIC IRQ affinity to CPU 0.
netsniff-ng --in team0 --out /opt/probe/ -s -m --interval 100MiB -b 0
Capture on an aggregated team0 networking device and dump packets into multiple
pcap files that are split into 100MiB each. Use mmap(2) I/O as a pcap write method,
support for super jumbo frames is built-in (does not need to be configured here),
and do not print the captured data to the terminal. Pin netsniff-ng and NIC IRQ
affinity to CPU 0. The default pcap magic type is 0xa1b2c3d4 (tcpdump-capable
pcap).
netsniff-ng --in vlan0 --out dump.pcap -c -u `id -u bob` -g `id -g bob`
Capture network traffic on device vlan0 into a pcap file called dump.pcap by using
normal read(2), write(2) I/O for the pcap file (slower but less latency). Also,
after setting up the RX_RING for capture, drop privileges from root to the user and
group “bob”. Invoke the packet dissector and print packet contents to the terminal
for further analysis.
netsniff-ng --in any --filter http.bpf -B --ascii -V
Capture from all available networking interfaces and install a low-level filter
that was previously compiled by bpfc(8) into http.bpf in order to filter HTTP
traffic. Super jumbo frame support is automatically enabled and only print human
readable packet data to the terminal, and also be more verbose during setup phase.
Moreover, dump a BPF disassembly of http.bpf.
netsniff-ng --in dump.pcap --out dump.cfg --silent
Convert the pcap file dump.pcap into a trafgen(8) configuration file dump.cfg. Do
not print pcap contents to the terminal.
netsniff-ng -i dump.pcap -f beacon.bpf -o -
Convert the pcap file dump.pcap into a trafgen(8) configuration file and write it
to stdout. However, do not dump all of its content, but only the one that passes
the low-level filter for raw 802.11 from beacon.bpf. The BPF engine here is invoked
in user space inside of netsniff-ng, so Linux extensions are not available.
cat foo.pcap | netsniff-ng -i - -o -
Read a pcap file from stdin and convert it into a trafgen(8) configuration file to
stdout.
netsniff-ng -i nlmon0 -o dump.pcap -s
Capture netlink traffic to a pcap file. This command needs a netlink monitoring
device to be set up beforehand using the follwing commands using ip(1) from the
iproute2 utility collection:
modprobe nlmon
ip link add type nlmon
ip link set nlmon0 up
To tear down the nlmon0 device, use the following commands:
ip link set nlmon0 down
ip link del dev nlmon0
rmmod nlmon
netsniff-ng --fanout-group 1 --fanout-type cpu --fanout-opts defrag --bind-cpu 0
--notouch-irq --silent --in em1 --out /var/cap/cpu0/ --interval 120sec
Start two netsniff-ng fanout instances. Both are assigned into the same fanout
group membership and traffic is splitted among them by incoming cpu. Furthermore,
the kernel is supposed to defragment possible incoming fragments. First instance is
assigned to CPU 0 and the second one to CPU 1, IRQ bindings are not altered as they
might have been adapted to this scenario by the user a-priori, and traffic is
captured on interface em1, and written out in 120 second intervals as pcap files
into /var/cap/cpu0/. Tools like mergecap(1) will be able to merge the cpu0/1 split
back together if needed.
CONFIG FILES
Files under /etc/netsniff-ng/ can be modified to extend netsniff-ng's functionality:
* oui.conf - OUI/MAC vendor database
* ether.conf - Ethernet type descriptions
* tcp.conf - TCP port/services map
* udp.conf - UDP port/services map
* geoip.conf - GeoIP database mirrors
FILTER EXAMPLE
netsniff-ng supports both, low-level and high-level filters that are attached to its
packet(7) socket. Low-level filters are described in the bpfc(8) man page.
Low-level filters can be used with netsniff-ng in the following way:
1. bpfc foo > bar
2. netsniff-ng -f bar
3. bpfc foo | netsniff-ng -i nlmon0 -f -
Here, foo is the bpfc program that will be translated into a netsniff-ng readable
“opcodes” file and passed to netsniff-ng through the -f option.
Similarly, high-level filter can be either passed through the -f option, e.g. -f "tcp or
udp" or at the end of all options without the “-f”.
The filter syntax is the same as in tcpdump(8), which is described in the man page pcap-
filter(7). Just to quote some examples:
host sundown
To select all packets arriving at or departing from sundown.
host helios and (hot or ace)
To select traffic between helios and either hot or ace.
ip host ace and not helios
To select all IP packets between ace and any host except helios.
net ucb-ether
To select all traffic between local hosts and hosts at Berkeley.
gateway snup and (port ftp or ftp-data)
To select all FTP traffic through Internet gateway snup.
ip and not net localnet
To select traffic neither sourced from, nor destined for, local hosts. If you have
a gateway to another network, this traffic should never make it onto your local
network.
tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net localnet
To select the start and end packets (the SYN and FIN packets) of each TCP
conversation that involve a non-local host.
tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)
To select all IPv4 HTTP packets to and from port 80, that is to say, print only
packets that contain data, not, for example, SYN and FIN packets and ACK-only
packets. (IPv6 is left as an exercise for the reader.)
gateway snup and ip[2:2] > 576
To select IP packets longer than 576 bytes sent through gateway snup.
ether[0] & 1 = 0 and ip[16] >= 224
To select IP broadcast or multicast packets that were not sent via Ethernet
broadcast or multicast.
icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply
To select all ICMP packets that are not echo requests or replies (that is to say,
not "ping" packets).
PCAP FORMATS:
netsniff-ng supports a couple of pcap formats, visible through ``netsniff-ng -D'':
tcpdump-capable pcap (default)
Pcap magic number is encoded as 0xa1b2c3d4 resp. 0xd4c3b2a1. As packet meta data
this format contains the timeval in microseconds, the original packet length and
the captured packet length.
tcpdump-capable pcap with ns resolution
Pcap magic number is encoded as 0xa1b23c4d resp. 0x4d3cb2a1. As packet meta data
this format contains the timeval in nanoseconds, the original packet length and the
captured packet length.
Alexey Kuznetzov's pcap
Pcap magic number is encoded as 0xa1b2cd34 resp. 0x34cdb2a1. As packet meta data
this format contains the timeval in microseconds, the original packet length, the
captured packet length, the interface index (sll_ifindex), the packet's protocol
(sll_protocol), and the packet type (sll_pkttype).
netsniff-ng pcap
Pcap magic number is encoded as 0xa1e2cb12 resp. 0x12cbe2a1. As packet meta data
this format contains the timeval in nanoseconds, the original packet length, the
captured packet length, the timestamp hw/sw source, the interface index
(sll_ifindex), the packet's protocol (sll_protocol), the packet type (sll_pkttype)
and the hardware type (sll_hatype).
For further implementation details or format support in your application, have a look at
pcap_io.h in the netsniff-ng sources.
NOTE
To avoid confusion, it should be noted that there is another network analyzer with a
similar name, called NetSniff, that is unrelated to the netsniff-ng project.
For introducing bit errors, delays with random variation and more while replaying pcaps,
make use of tc(8) with its disciplines such as netem.
netsniff-ng does only some basic, architecture generic tuning on startup. If you are
considering to do high performance capturing, you need to carefully tune your machine,
both hardware and software. Simply letting netsniff-ng run without thinking about your
underlying system might not necessarily give you the desired performance. Note that tuning
your system is always a tradeoff and fine-grained balancing act (throughput versus
latency). You should know what you are doing!
One recommendation for software-based tuning is tuned(8). Besides that, there are many
other things to consider. Just to throw you a few things that you might want to look at:
NAPI networking drivers, tickless kernel, I/OAT DMA engine, Direct Cache Access, RAM-based
file systems, multi-queues, and many more things. Also, you might want to read the
kernel's Documentation/networking/scaling.txt file regarding technologies such as RSS,
RPS, RFS, aRFS and XPS. Also check your ethtool(8) settings, for example regarding
offloading or Ethernet pause frames.
Moreover, to get a deeper understanding of netsniff-ng internals and how it interacts with
the Linux kernel, the kernel documentation under
Documentation/networking/{packet_mmap.txt, filter.txt, multiqueue.txt} might be of
interest.
How do you sniff in a switched environment? I rudely refer to dSniff's documentation that
says:
The easiest route is simply to impersonate the local gateway, stealing client traffic en
route to some remote destination. Of course, the traffic must be forwarded by your
attacking machine, either by enabling kernel IP forwarding or with a userland program that
accomplishes the same (fragrouter -B1).
Several people have reportedly destroyed connectivity on their LAN to the outside world by
ARP spoofing the gateway, and forgetting to enable IP forwarding on the attacking machine.
Do not do this. You have been warned.
A safer option than ARP spoofing would be to use a "port mirror" function if your switch
hardware supports it and if you have access to the switch.
If you do not need to dump all possible traffic, you have to consider running netsniff-ng
with a BPF filter for the ingress path. For that purpose, read the bpfc(8) man page.
Also, to aggregate multiple NICs that you want to capture on, you should consider using
team devices, further explained in libteam resp. teamd(8).
The following netsniff-ng pcap magic numbers are compatible with other tools, at least
tcpdump or Wireshark:
0xa1b2c3d4 (tcpdump-capable pcap)
0xa1b23c4d (tcpdump-capable pcap with ns resolution)
0xa1b2cd34 (Alexey Kuznetzov's pcap)
Pcap files with different meta data endianness are supported by netsniff-ng as well.
BUGS
When replaying pcap files, the timing information from the pcap packet header is currently
ignored.
Also, when replaying pcap files, demultiplexing traffic among multiple networking
interfaces does not work. Currently, it is only sent via the interface that is given by
the --out parameter.
When performing traffic capture on the Ethernet interface, the pcap file is created and
packets are received but without a 802.1Q header. When one uses tshark, all headers are
visible, but netsniff-ng removes 802.1Q headers. Is that normal behavior?
Yes and no. The way VLAN headers are handled in PF_PACKET sockets by the kernel is
somewhat “problematic” [1]. The problem in the Linux kernel is that some drivers already
handle VLANs, others do not. Those who handle it can have different implementations, such
as hardware acceleration and so on. So in some cases the VLAN tag is even stripped before
entering the protocol stack, in some cases probably not. The bottom line is that a "hack"
was introduced in PF_PACKET so that a VLAN ID is visible in some helper data structure
that is accessible from the RX_RING.
Then it gets really messy in the user space to artificially put the VLAN header back into
the right place. Not to mention the resulting performance implications on all of
libpcap(3) tools since parts of the packet need to be copied for reassembly via
memmove(3).
A user reported the following, just to demonstrate this mess: some tests were made with
two machines, and it seems that results depend on the driver ...
AR8131:
ethtool -k eth0 gives "rx-vlan-offload: on"
- wireshark gets the vlan header
- netsniff-ng doesn't get the vlan header
ethtool -K eth0 rxvlan off
- wireshark gets a QinQ header even though no one sent QinQ
- netsniff-ng gets the vlan header
RTL8111/8168B:
ethtool -k eth0 gives "rx-vlan-offload: on"
- wireshark gets the vlan header
- netsniff-ng doesn't get the vlan header
ethtool -K eth0 rxvlan off
- wireshark gets the vlan header
- netsniff-ng doesn't get the vlan header
Even if we agreed on doing the same workaround as libpcap, we still will not be able to
see QinQ, for instance, due to the fact that only one VLAN tag is stored in the kernel
helper data structure. We think that there should be a good consensus on the kernel space
side about what gets transferred to userland first.
Update (28.11.2012): the Linux kernel and also bpfc(8) has built-in support for hardware
accelerated VLAN filtering, even though tags might not be visible in the payload itself as
reported here. However, the filtering for VLANs works reliable if your NIC supports it.
See bpfc(8) for an example.
[1] http://lkml.indiana.edu/hypermail/linux/kernel/0710.3/3816.html
[2] http://www.tcpdump.org/linktypes/LINKTYPE_NETLINK.html
[3] http://www.tcpdump.org/linktypes/LINKTYPE_LINUX_SLL.html
LEGAL
netsniff-ng is licensed under the GNU GPL version 2.0.
HISTORY
netsniff-ng was originally written for the netsniff-ng toolkit by Daniel Borkmann. Bigger
contributions were made by Emmanuel Roullit, Markus Amend, Tobias Klauser and Christoph
Jaeger. It is currently maintained by Tobias Klauser <tklauser@distanz.ch> and Daniel
Borkmann <dborkma@tik.ee.ethz.ch>.
SEE ALSO
trafgen(8), mausezahn(8), ifpps(8), bpfc(8), flowtop(8), astraceroute(8), curvetun(8)
AUTHOR
Manpage was written by Daniel Borkmann.
COLOPHON
This page is part of the Linux netsniff-ng toolkit project. A description of the project,
and information about reporting bugs, can be found at http://netsniff-ng.org/.