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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | USAGE EXAMPLE | CONFIG FILES | FILTER EXAMPLE | PCAP FORMATS: | NOTE | BUGS | LEGAL | HISTORY | SEE ALSO | AUTHOR | COLOPHON | COLOPHON |
NETSNIFF-NG(8) netsniff-ng toolkit NETSNIFF-NG(8)
netsniff-ng - the packet sniffing beast
netsniff-ng { [options] [filter-expression] }
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. It has different pcap I/O
methods supported (scatter-gather, mmap(2), read(2), and write(2))
for efficient to-disc capturing. 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 pcaps
into a single large pcap. Thus, netsniff-ng then works multithreaded
eventually.
netsniff-ng can also be used to debug netlink traffic.
-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 (“-”).
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. In case 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.
-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.
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.
modprobe nlmon
ip link add type nlmon
ip link set nlmon0 up
netsniff-ng -i nlmon0 -o dump.pcap -s
ip link set nlmon0 down
ip link del dev nlmon0
rmmod nlmon
In this example, netlink traffic is being captured. If not already
done, a netlink monitoring device needs to be set up before it can be
used to capture netlink socket buffers (iproute2's ip(1) commands are
given for nlmon device setup and teardown). netsniff-ng can then make
use of the nlmon device as an input device. In this example a pcap
file with netlink traffic is being recorded.
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
netsniff-ng --fanout-group 1 --fanout-type cpu --fanout-opts defrag
--bind-cpu 1 --notouch-irq --silent --in em1 --out /var/cap/cpu1/
--interval 120sec
Starts 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.
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
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 from pcap-
filter(7):
host sundown
To select all packets arriving at or departing from sundown.
host helios and ˛t 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).
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.
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.
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
netsniff-ng is licensed under the GNU GPL version 2.0.
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>.
trafgen(8), mausezahn(8), ifpps(8), bpfc(8), flowtop(8),
astraceroute(8), curvetun(8)
Manpage was written by Daniel Borkmann.
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/.
This page is part of the netsniff-ng (a free Linux networking
toolkit) project. Information about the project can be found at
⟨http://netsniff-ng.org/⟩. If you have a bug report for this manual
page, send it to netsniff-ng@googlegroups.com. This page was
obtained from the project's upstream Git repository
⟨git://github.com/netsniff-ng/netsniff-ng.git⟩ on 2017-07-05. If you
discover any rendering problems in this HTML version of the page, or
you believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
Linux 03 March 2013 NETSNIFF-NG(8)
Pages that refer to this page: astraceroute(8), bpfc(8), curvetun(8), flowtop(8), ifpps(8), mausezahn(8), trafgen(8)