Provided by: netsniff-ng_0.6.0-1build2_amd64 
NAME
trafgen - a fast, multithreaded network packet generator
SYNOPSIS
trafgen [options]
DESCRIPTION
trafgen 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 powerful 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 operating systems, same as netsniff-
ng(8), thus we can keep the code footprint 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 configuration can be built with random
numbers on all or certain packet offsets 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 trafgen 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 configuration file has passed the C preprocessor
stage, it is processed by the trafgen packet compiler. The language itself supports a couple of features
that are useful when assembling packets, such as built-in runtime checksum support for IP, UDP and TCP.
Also it has an expression evaluator 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
scenario.
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
configuration 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 disadvantage 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 possible 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 configuration 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 running 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 <time>, --gap <time>
Specify a static inter-packet timegap in seconds, milliseconds, microseconds, or nanoseconds:
''<num>s/ms/us/ns''. If no postfix is given default to microseconds. 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
<time> 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 patterns. Furthermore, the TX_RING interface does not cope with interpacket 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 connectivity rate.
-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.
-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.
-A, --no-sock-mem
Do not change systems default socket memory setting during testrun. Default is to boost socket buffer
memory during the test to:
/proc/sys/net/core/rmem_default:4194304
/proc/sys/net/core/wmem_default:4194304
/proc/sys/net/core/rmem_max:104857600
/proc/sys/net/core/wmem_max:104857600
-Q, --notouch-irq
Do not reassign the NIC's IRQ CPU affinity settings.
-q, --qdisc-path
Since Linux 3.14, the kernel supports a socket option PACKET_QDISC_BYPASS, which trafgen enables by
default. This options disables the qdisc bypass, and uses the normal send path through the kernel's
qdisc (traffic control) layer, which can be usefully for testing the qdisc path.
-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
packets. 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>)
UDP checksum (IPv6): csumudp6(<off-ip6hdr>, <off-udpdr>)
TCP checksum (IPv6): csumtcp6(<off-ip6hdr>, <off-tcphdr>)
iii) Multibyte functions, compile-time expression evaluation:
const8(<content>), c8(<content>), const16(<content>), c16(<content>),
const32(<content>), c32(<content>), const64(<content>), c64(<content>)
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 preprocessor 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 EXAMPLE
trafgen --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 ''trafgen.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
compiler 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
''beacon-test.txf'' configuration file, set trafgen into verbose mode and use only 2 CPUs.
trafgen --dev em1 --conf frag_dos.cfg --rand --gap 1000us
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 transmission 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.
NOTE
trafgen can saturate a Gigabit Ethernet link without problems. As always, of course, this depends on your
hardware as well. Not everywhere where it says Gigabit Ethernet on the box, will you reach almost
physical line rate! Please also read the netsniff-ng(8) man page, section 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 existing 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 independent 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
together 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 proprietary (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.
LEGAL
trafgen is licensed under the GNU GPL version 2.0.
HISTORY
trafgen was originally written for the netsniff-ng toolkit by Daniel Borkmann. It is currently maintained
by Tobias Klauser <tklauser@distanz.ch> and Daniel Borkmann <dborkma@tik.ee.ethz.ch>.
SEE ALSO
netsniff-ng(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/.
Linux 03 March 2013 TRAFGEN(8)