TRAFGEN(8) netsniff-ng toolkit TRAFGEN(8)NAMEtrafgen - a fast, multithreaded network packet generator
SYNOPSIStrafgen [options]
DESCRIPTIONtrafgen is a fast, zero-copy network traffic generator for debugging,
performance evaluation, and fuzz-testing. trafgen utilizes the
packet(7) socket interface of Linux which postpones complete control
over packet data and packet headers into the user space. It has a pow‐
erful packet configuration language, which is rather low-level and not
limited to particular protocols. Thus, trafgen can be used for many
purposes. Its only limitation is that it cannot mimic full streams
resp. sessions. However, it is very useful for various kinds of load
testing in order to analyze and subsequently improve systems behaviour
under DoS attack scenarios, for instance.
trafgen is Linux specific, meaning there is no support for other oper‐
ating systems, same as netsniff-ng(8), thus we can keep the code foot‐
print quite minimal and to the point. trafgen makes use of packet(7)
socket's TX_RING interface of the Linux kernel, which is a mmap(2)'ed
ring buffer shared between user and kernel space.
By default, trafgen starts as many processes as available CPUs, pins
each of them to their respective CPU and sets up the ring buffer each
in their own process space after having compiled a list of packets to
transmit. Thus, this is likely the fastest one can get out of the box
in terms of transmission performance from user space, without having to
load unsupported or non-mainline third-party kernel modules. On Gigabit
Ethernet, trafgen has a comparable performance to pktgen, the built-in
Linux kernel traffic generator, except that trafgen is more flexible in
terms of packet configuration possibilities. On 10-Gigabit-per-second
Ethernet, trafgen might be slower than pktgen due to the user/kernel
space overhead but still has a fairly high performance for out of the
box kernels.
trafgen has the potential to do fuzz testing, meaning a packet configu‐
ration can be built with random numbers on all or certain packet off‐
sets that are freshly generated each time a packet is sent out. With a
built-in IPv4 ping, trafgen can send out an ICMP probe after each
packet injection to the remote host in order to test if it is still
responsive/alive. Assuming there is no answer from the remote host
after a certain threshold of probes, the machine is considered dead and
the last sent packet is printed together with the random seed that was
used by trafgen. You might not really get lucky fuzz-testing the Linux
kernel, but presumably there are buggy closed-source embedded systems
or network driver's firmware files that are prone to bugs, where traf‐
gen could help in finding them.
trafgen's configuration language is quite powerful, also due to the
fact, that it supports C preprocessor macros. A stddef.h is being
shipped with trafgen for this purpose, so that well known defines from
Linux kernel or network programming can be reused. After a configura‐
tion file has passed the C preprocessor stage, it is processed by the
trafgen packet compiler. The language itself supports a couple of fea‐
tures that are useful when assembling packets, such as built-in runtime
checksum support for IP, UDP and TCP. Also it has an expression evalua‐
tor where arithmetic (basic operations, bit operations, bit shifting,
...) on constant expressions is being reduced to a single constant on
compile time. Other features are ''fill'' macros, where a packet can be
filled with n bytes by a constant, a compile-time random number or run-
time random number (as mentioned with fuzz testing). Also, netsniff-
ng(8) is able to convert a pcap file into a trafgen configuration file,
thus such a configuration can then be further tweaked for a given sce‐
nario.
OPTIONS-i <cfg|->, -c <cfg|i>, --in <cfg|->, --conf <cfg|->
Defines the input configuration file that can either be passed as a
normal plain text file or via stdin (''-''). Note that currently, if a
configuration is passed through stdin, only 1 CPU will be used.
-o <dev>, -d <dev>, --out <dev>, --dev <dev>
Defines the outgoing networking device such as eth0, wlan0 and others.
-p, --cpp
Pass the packet configuration to the C preprocessor before reading it
into trafgen. This allows #define and #include directives (e.g. to
include definitions from system headers) to be used in the trafgen con‐
figuration file.
-J, --jumbo-support
By default trafgen's ring buffer frames are of a fixed size of 2048
bytes. This means that if you're expecting jumbo frames or even super
jumbo frames to pass your line, then you will need to enable support
for that with the help of this option. However, this has the disadvan‐
tage of a performance regression and a bigger memory footprint for the
ring buffer.
-R, --rfraw
In case the output networking device is a wireless device, it is possi‐
ble with trafgen to turn this into monitor mode and create a mon<X>
device that trafgen will be transmitting on instead of wlan<X>, for
instance. This enables trafgen to inject raw 802.11 frames.
-s <ipv4>, --smoke-test <ipv4>
In case this option is enabled, trafgen will perform a smoke test. In
other words, it will probe the remote end, specified by an <ipv4>
address, that is being ''attacked'' with trafgen network traffic, if it
is still alive and responsive. That means, after each transmitted
packet that has been configured, trafgen sends out ICMP echo requests
and waits for an answer before it continues. In case the remote end
stays unresponsive, trafgen assumes that the machine has crashed and
will print out the content of the last packet as a trafgen packet con‐
figuration and the random seed that has been used in order to reproduce
a possible bug. This might be useful when testing proprietary embedded
devices. It is recommended to have a direct link between the host run‐
ning trafgen and the host being attacked by trafgen.
-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.
-r, --rand
Randomize the packet selection of the configuration file. By default,
if more than one packet is defined in a packet configuration, packets
are scheduled for transmission in a round robin fashion. With this
option, they are selected randomly instread.
-P <uint>, --cpus <uint>
Specify the number of processes trafgen shall fork(2) off. By default
trafgen will start as many processes as CPUs that are online and pin
them to each, respectively. Allowed value must be within interval
[1,CPUs].
-t <uint>, --gap <uint>
Specify a static inter-packet timegap in micro-seconds. If this option
is given, then instead of packet(7)'s TX_RING interface, trafgen will
use sendto(2) I/O for network packets, even if the <uint> argument is
0. This option is useful for a couple of reasons: i) comparison between
sendto(2) and TX_RING performance, ii) low-traffic packet probing for a
given interval, iii) ping-like debugging with specific payload pat‐
terns. Furthermore, the TX_RING interface does not cope with inter‐
packet gaps.
-S <size>, --ring-size <size>
Manually define the TX_RING resp. TX_RING size in ''<num>KiB/MiB/GiB''.
On default the size is being determined based on the network connectiv‐
ity 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..
-E <uint>, --seed <uint>
Manually set the seed for pseudo random number generator (PRNG) in
trafgen. By default, a random seed from /dev/urandom is used to feed
glibc's PRNG. If that fails, it falls back to the unix timestamp. It
can be useful to set the seed manually in order to be able to reproduce
a trafgen session, e.g. after fuzz testing.
-u <uid>, --user <uid> resp. -g <gid>, --group <gid>
After ring setup, drop privileges to a non-root user/group combination.
-V, --verbose
Let trafgen be more talkative and let it print the parsed configuration
and some ring buffer statistics.
-e, --example
Show a built-in packet configuration example. This might be a good
starting point for an initial packet configuration scenario.
-C, --no-cpu-stats
Do not print CPU time statistics on exit.
-v, --version
Show version information and exit.
-h, --help
Show user help and exit.
SYNTAX
trafgen's packet configuration syntax is fairly simple. The very basic
things one needs to know is that a configuration file is a simple plain
text file where packets are defined. It can contain one or more pack‐
ets. Packets are enclosed by opening '{' and closing '}' braces, for
example:
{ /* packet 1 content goes here ... */ }
{ /* packet 2 content goes here ... */ }
When trafgen is started using multiple CPUs (default), then each of
those packets will be scheduled for transmission on all CPUs by
default. However, it is possible to tell trafgen to schedule a packet
only on a particular CPU:
cpu(1): { /* packet 1 content goes here ... */ }
cpu(2-3): { /* packet 2 content goes here ... */ }
Thus, in case we have a 4 core machine with CPU0-CPU3, packet 1 will be
scheduled only on CPU1, packet 2 on CPU2 and CPU3. When using trafgen
with --num option, then these constraints will still be valid and the
packet is fairly distributed among those CPUs.
Packet content is delimited either by a comma or whitespace, or both:
{ 0xca, 0xfe, 0xba 0xbe }
Packet content can be of the following:
hex bytes: 0xca, xff
decimal: 42
binary: 0b11110000, b11110000
octal: 011
character: 'a'
string: "hello world"
shellcode: "\x31\xdb\x8d\x43\x17\x99\xcd\x80\x31\xc9"
Thus, a quite useless packet packet configuration might look like this
(one can verify this when running this with trafgen in combination with
-V):
{ 0xca, 42, 0b11110000, 011, 'a', "hello world",
"\x31\xdb\x8d\x43\x17\x99\xcd\x80\x31\xc9" }
There are a couple of helper functions in trafgen's language to make
life easier to write configurations:
i) Fill with garbage functions:
byte fill function: fill(<content>, <times>): fill(0xca, 128)
compile-time random: rnd(<times>): rnd(128), rnd()
runtime random numbers: drnd(<times>): drnd(128), drnd()
compile-time counter: seqinc(<start-val>, <increment>, <times>)
seqdec(<start-val>, <decrement>, <times>)
runtime counter (1byte): dinc(<min-val>, <max-val>, <increment>)
ddec(<min-val>, <max-val>, <decrement>)
ii) Checksum helper functions (packet offsets start with 0):
IP/ICMP checksum: csumip/csumicmp(<off-from>, <off-to>)
UDP checksum: csumudp(<off-iphdr>, <off-udpdr>)
TCP checksum: csumtcp(<off-iphdr>, <off-tcphdr>)
iii) Multibyte functions, compile-time expression evaluation:
const8(<content>), c8(<content>), const16(<content>), c16(<con‐
tent>),
const32(<content>), c32(<content>), const64(<content>), c64(<con‐
tent>)
These functions write their result in network byte order into the
packet configuration, e.g. const16(0xaa) will result in ''00 aa''.
Within c*() functions, it is possible to do some arithmetics:
-,+,*,/,%,&,|,<<,>>,^ E.g. const16((((1<<8)+0x32)|0b110)*2) will be
evaluated to ''02 6c''.
Furthermore, there are two types of comments in trafgen configuration
files:
1. Multi-line C-style comments: /* put comment here */
2. Single-line Shell-style comments: # put comment here
Next to all of this, a configuration can be passed through the C pre‐
processor before the trafgen compiler gets to see it with option --cpp.
To give you a taste of a more advanced example, run ''trafgen -e'',
fields are commented:
/* Note: dynamic elements make trafgen slower! */
#include <stddef.h>
{
/* MAC Destination */
fill(0xff, ETH_ALEN),
/* MAC Source */
0x00, 0x02, 0xb3, drnd(3),
/* IPv4 Protocol */
c16(ETH_P_IP),
/* IPv4 Version, IHL, TOS */
0b01000101, 0,
/* IPv4 Total Len */
c16(59),
/* IPv4 Ident */
drnd(2),
/* IPv4 Flags, Frag Off */
0b01000000, 0,
/* IPv4 TTL */
64,
/* Proto TCP */
0x06,
/* IPv4 Checksum (IP header from, to) */
csumip(14, 33),
/* Source IP */
drnd(4),
/* Dest IP */
drnd(4),
/* TCP Source Port */
drnd(2),
/* TCP Dest Port */
c16(80),
/* TCP Sequence Number */
drnd(4),
/* TCP Ackn. Number */
c32(0),
/* TCP Header length + TCP SYN/ECN Flag */
c16((8 << 12) | TCP_FLAG_SYN | TCP_FLAG_ECE)
/* Window Size */
c16(16),
/* TCP Checksum (offset IP, offset TCP) */
csumtcp(14, 34),
/* TCP Options */
0x00, 0x00, 0x01, 0x01, 0x08, 0x0a, 0x06,
0x91, 0x68, 0x7d, 0x06, 0x91, 0x68, 0x6f,
/* Data blob */
"gotcha!",
}
Another real-world example by Jesper Dangaard Brouer [1]:
{
# --- ethernet header ---
0x00, 0x1b, 0x21, 0x3c, 0x9d, 0xf8, # mac destination
0x90, 0xe2, 0xba, 0x0a, 0x56, 0xb4, # mac source
const16(0x0800), # protocol
# --- ip header ---
# ipv4 version (4-bit) + ihl (4-bit), tos
0b01000101, 0,
# ipv4 total len
const16(40),
# id (note: runtime dynamic random)
drnd(2),
# ipv4 3-bit flags + 13-bit fragment offset
# 001 = more fragments
0b00100000, 0,
64, # ttl
17, # proto udp
# dynamic ip checksum (note: offsets are zero indexed)
csumip(14, 33),
192, 168, 51, 1, # source ip
192, 168, 51, 2, # dest ip
# --- udp header ---
# as this is a fragment the below stuff does not matter too much
const16(48054), # src port
const16(43514), # dst port
const16(20), # udp length
# udp checksum can be dyn calc via csumudp(offset ip, offset tcp)
# which is csumudp(14, 34), but for udp its allowed to be zero
const16(0),
# payload
'A', fill(0x41, 11),
}
[1] http://thread.gmane.org/gmane.linux.network/257155
USAGE EXAMPLEtrafgen--dev eth0 --conf trafgen.cfg
This is the most simple and, probably, the most common use of trafgen.
It will generate traffic defined in the configuration file ''traf‐
gen.cfg'' and transmit this via the ''eth0'' networking device. All
online CPUs are used.
trafgen-e | trafgen-i - -o lo --cpp -n 1
This is an example where we send one packet of the built-in example
through the loopback device. The example configuration is passed via
stdin and also through the C preprocessor before trafgen's packet com‐
piler will see it.
trafgen--dev eth0 --conf fuzzing.cfg --smoke-test 10.0.0.1
Read the ''fuzzing.cfg'' packet configuration file (which contains
drnd() calls) and send out the generated packets to the ''eth0''
device. After each sent packet, ping probe the attacked host with
address 10.0.0.1 to check if it's still alive. This also means, that we
utilize 1 CPU only, and do not use the TX_RING, but sendto(2) packet
I/O due to ''slow mode''.
trafgen--dev wlan0 --rfraw --conf beacon-test.txf -V --cpus 2
As an output device ''wlan0'' is used and put into monitoring mode,
thus we are going to transmit raw 802.11 frames through the air. Use
the use only 2 CPUs.
trafgen--dev em1 --conf frag_dos.cfg --rand --gap 1000
Use trafgen in sendto(2) mode instead of TX_RING mode and sleep after
each sent packet a static timegap for 1000us. Generate packets from
''frag_dos.cfg'' and select next packets to send randomly instead of a
round-robin fashion. The output device for packets is ''em1''.
trafgen--dev eth0 --conf icmp.cfg --rand --num 1400000 -k1000
Send only 1400000 packets using the ''icmp.cfg'' configuration file and
then exit trafgen. Select packets randomly from that file for transmis‐
sion and send them out via ''eth0''. Also, trigger the kernel every
1000us for batching the ring frames from user space (default is 10us).
trafgen--dev eth0 --conf tcp_syn.cfg -u `id -u bob` -g `id -g bob`
Send out packets generated from the configuration file ''tcp_syn.cfg''
via the ''eth0'' networking device. After setting up the ring for
transmission, drop credentials to the non-root user/group bob/bob.
NOTEtrafgen can saturate a Gigabit Ethernet link without problems. As
always, of course, this depends on your hardware as well. Not every‐
where where it says Gigabit Ethernet on the box, will you reach almost
physical line rate! Please also read the netsniff-ng(8) man page, sec‐
tion NOTE for further details about tuning your system e.g. with
tuned(8).
If you intend to use trafgen on a 10-Gbit/s Ethernet NIC, make sure you
are using a multiqueue tc(8) discipline, and make sure that the packets
you generate with trafgen will have a good distribution among tx_hashes
so that you'll actually make use of multiqueues.
For introducing bit errors, delays with random variation and more,
there is no built-in option in trafgen. Rather, one should reuse exist‐
ing methods for that which integrate nicely with trafgen, such as tc(8)
with its different disciplines, i.e. netem.
For more complex packet configurations, it is recommended to use high-
level scripting for generating trafgen packet configurations in a more
automated way, i.e. also to create different traffic distributions that
are common for industrial benchmarking:
Traffic model Distribution
IMIX 64:7, 570:4, 1518:1
Tolly 64:55, 78:5, 576:17, 1518:23
Cisco 64:7, 594:4, 1518:1
RPR Trimodal 64:60, 512:20, 1518:20
RPR Quadrimodal 64:50, 512:15, 1518:15, 9218:20
The low-level nature of trafgen makes trafgen rather protocol indepen‐
dent and therefore useful in many scenarios when stress testing is
needed, for instance. However, if a traffic generator with higher level
packet descriptions is desired, netsniff-ng's mausezahn(8) can be of
good use as well.
For smoke/fuzz testing with trafgen, it is recommended to have a direct
link between the host you want to analyze (''victim'' machine) and the
host you run trafgen on (''attacker'' machine). If the ICMP reply from
the victim fails, we assume that probably its kernel crashed, thus we
print the last sent packet togther with the seed and quit probing. It
might be very unlikely to find such a ping-of-death on modern Linux
systems. However, there might be a good chance to find it on some pro‐
prietary (e.g. embedded) systems or buggy driver firmwares that are in
the wild. Also, fuzz testing can be done on raw 802.11 frames, of
course. In case you find a ping-of-death, please mention that you were
using trafgen in your commit message of the fix!
BUGS
For old trafgen versions only, there could occur kernel crashes: we
have fixed this bug in the mainline and stable kernels under commit
7f5c3e3a8 (''af_packet: remove BUG statement in tpacket_destruct_skb'')
and also in trafgen.
Probably the best is if you upgrade trafgen to the latest version.
LEGALtrafgen is licensed under the GNU GPL version 2.0.
HISTORYtrafgen was originally written for the netsniff-ng toolkit by Daniel
Borkmann. It is currently maintained by Tobias Klauser <tklauser@dis‐
tanz.ch> and Daniel Borkmann <dborkma@tik.ee.ethz.ch>.
SEE ALSOnetsniff-ng(8), mausezahn(8), ifpps(8), bpfc(8), flowtop(8), astracer‐
oute(8), curvetun(8)AUTHOR
Manpage was written by Daniel Borkmann.
COLOPHON
This page is part of the Linux netsniff-ng toolkit project. A descrip‐
tion of the project, and information about reporting bugs, can be found
at http://netsniff-ng.org/.
Linux 03 March 2013 TRAFGEN(8)
