nttcp(1)nttcp(1)NAMEnttcp - new test TCP program
SYNOPSISnttcp [ local options ] partner-host [ partner-host ] ... [ remote
options ]
DESCRIPTION
The nttcp program measures the transferrate (and other numbers) on a
TCP, UDP or UDP multicast connection. To use nttcp you have to provide
the executable on the local machine and on a partner machine. On the
partner machine simply start nttcp with the option -i. Started this
way, nttcp is waiting for connections from other nttcps. On the local
host simply call nttcp with the name of the partner host. It will con‐
tact the nttcp started on the partner machine and initiate the trans‐
fer. On default the program transfers 2048 buffers of 4KByte length (a
total of 8 MByte) to the partner host. On both sides the performance
will be measured and the findings (both, remote and local) are reported
on the local side. You may change nearly every parameter of the trans‐
mission via commandline options, even what and how results are printed.
OPTIONS-r defines the receive transfer direction; data is sent from the
partner host to the local host.
-t defines the transmit transfer direction; data is sent from the
local host to the partner host. This is the default direction.
-T Print a title line.
-u Use the UDP protocol instead of TCP (which is the default).
-g Gap time in microseconds between packets. This delay is imple‐
mented via the timeout parameter of select(2) and a loop with
gettimeofday(2). The accuracy of this value is misleading. Most
machines will not be able to delay exactly the given amount.
The code will try its best to achieve the desired delay. For TCP
connections this option does only implement a delay between the
write(2) system calls. It does not really delay between the real
output on the physical device.
-v Give more and verbose output; only useful for debugging pur‐
poses.
-D Set the TCP_NODELAY option on the transmitting socket. With
this option set, the socket does not buffer any write requests.
-f format string
Specify your own output format. See OUTPUT.
-n number of buffers
The given number of buffers will be written to the transmitting
socket. It defaults to 2048.
-l length of buffer
The given length defines the size of one buffer written to the
transmitting socket. Defaults to 4096.
-x fixed length of data
The given length defines the amount of data that will be trans‐
fered. Subsequent specified -l or -n options will adapt the
corresponding other value so that the number of buffers and the
length of buffer multiplies to the given fixed length.
-w number of kilo bytes
Defines the buffer size of the transmitting and receiving
socket. This is system dependant; usally it is 16K.
-c If this option is present, the receiving side will compare the
bytes received with the pattern used by the sending side. At
most the first 100 differences will be reported. If the trans‐
mission is via TCP, a uniq pattern for the whole transmission is
generated. For UDP the same pattern for each paket is used. You
can force a stream pattern with the -s switch; but if one paket
is lost, all subsequent packets contain patterns not expected
and will be reported as different. Since every byte is numbered,
this can be used to detect the first packet lost during the
transmission.
BUT be aware: if there is a difference, this option may lead to
packet-losses on UDP transmissions or to degration in perfor‐
mance, since the preparation of the output is simple-minded and
uses a lot of CPU time.
-s Forces the generation of a stream pattern if UPD packet data is
compared. See -c switch.
-S seed string
give any string to initialize the pattern generator. By default
this seed has the value 'This is a simple init string'. This
enforces the -c option.
-pport number
On default the partner host will listen on port 5037. This can
be overwritten with this option.
-i If you have no root access on the partner host, or do not want
hacking with inetd, this option directs nttcp to behave as a
daemon, waiting for connections and spawning off child processes
by itself as inetd would do it otherwise.
-Rnumber of getpid() calls
This option does not transmit any data, but calls the given num‐
ber of times getpid(2) and calculates the number of calls per
second. This is a measure for the speed of the machine and the
system call interface.
-mmulticast IP:port
This option is used to force sending to the specified multicast
address and port. This option enforces the -u and-t
switch.AlsoseeMULTICASTlaterinthisdocument.
OUTPUT
The output of the program consists of two lines of numbers; or more
lines if used in transmitting to more than one machine (multicasting).
The first line for the measures of the local host the other line for
the measure of the partner host. This is also indicated with the first
characters beeing a 'l' respective 'r'. If the -T flag was given, also
a Title line is given. The default format of the outout looks like
this:
Bytes Real s CPU s Real-MBit/s CPU-MBit/s Calls Real-C/s CPU-C/s
l 8388608 7.51 0.25 8.7307 259.8676 2048 272.83 8120.86
r 8388608 7.55 0.95 8.6804 68.9853 3831 507.42 4032.63
The timing and rate values marked with 'CPU' use the sum of system and
user time only. Real timing and rate values are computed using the time
from the begin to the end of the transmission.
It is possible to specify another form of the output. This is done sim‐
iliar to the format strings of printf(3s). The conversion characters of
printf(3s) are replaced with the following tags. Each tag is preceded
by '%' as in printf(3s). Between the '%' character and the tag there
are width and precision specifications allowed as with printf(3s). Two
types of values are printed integers and floats. For these types the
conversion letters 'd' respective 'f' of printf(3s) are used.
l prints the buffer length in bytes. Integer value.
n prints the buffer count. Integer value.
c prints the number of calls. Integer value.
rt prints the real time in s. Float value.
rbr prints the real bit rate in MBit/s. Float value.
rcr prints the real call rate in calls/s. Float value.
ct prints the cpu time in s. Float value.
cbr prints the cpu bit rate in MBit/s. Float value.
ccr prints the cpu call rate in calls/s. Float value.
The default format is produced with the following format string:
"%9b%8.2rt%8.2ct%12.4rbr%12.4cbr%8c%10.2rcr%10.2ccr"
INSTALLATION
To make most convenient use of this program, it can be installed on the
partner machine, so that inetd(8) can start it. To accomplish this, two
files have to be edited: /etc/inetd.conf and /etc/services.
The respective lines may look like this:
inetd.conf:
ttcp stream tcp nowait nobody /usr/local/etc/nttcp nttcp
services:
ttcp 5037/tcp # to measure tcp transfer rates
After these changes have been made, the inetd(8) process has to be
notified via a HUP signal (or killed and restarted on older versions of
unix).
MULTICASTING
Beginning with version 1.4 there is support generating multicast traf‐
fic. You even needn't set any option, but simply specify more than one
partner host. This mode is restricted to sending packets from the local
host to the partner hosts. And of course works only on machines that
have a multicast enabled IP stack. Tested is this feature on
Solaris2.6, HPUX-10 and HPUX-11 and Irix 6.2. Also FreeBSD-2.2.6 com‐
piled with option MROUTING works. But be aware what this means to your
networking environment. Most ethernet switches for example handle mul‐
ticast traffic as broadcast. This way you will flood your complete
network with these packets.
ENVIRONMENT
The are two environment variables NTTCP_LOC_OPT and NTTCP_REM_OPT that
can be used to preset the local options and remote options respectivly.
They take the same format as the commandline does. Commandline options
override those settings from the environment.
SECURITY
Under security considerations, the inetd-mode of operation is NOT sug‐
gested. Hosts configured to start nttcp this way, are very open to
denial-of-service attacks. If you are concerned about this issue, you
should consider either the use of tcpwrapper or simply not install
nttcp this way.
Also be sure to run nttcp as non-root when started via inetd(8). I have
taken some care to avoid buffer-overrun prone coding. But the source is
too big now to be sure in all corners of the code.
You may also consider not to provide general access to this programm.
It may easily be used to flood your network with lots of traffic. This
may be used to launch or support denial-of-service attacks.
WARNING
There are a lot of pitfalls in explaining unexpected measures. Be sure
to get a thorough understanding of your network and the devices used
and installed. Also it is extremly helpful to have a deep understanding
of the things that happen in your machine and operating system. A short
example shows what is meant here: If you see packet losses on UDP
transfers, it may be, that the packets are lost on the sending host!
For today machines it is easy to produce packets much faster than a
10MBit ethernet can swallow it, so they may be dropped on the UDP stack
of the operating system. This depends on the implementation of your IP
stack. So, to be sure, use a second machine, and snoop or tcpdump the
traffic in question, to be sure what happens on the medium.
BUGS
Any program without bugs?
SEE ALSOinetd(8).
HISTORY
This program was written to ease the measurement of TCP transfer rates
in a network of unix workstations. It is based on the ttcp.c program,
which was (I suppose) posted to comp.sources.misc. This man-page
describes version 1.4.
AUTHOR
Elmar Bartel
Fakultaet fuer Informatik,
Technische Universitaet Muenchen.
bartel@informatik.tu-muenchen.de
5 Oct 1998 nttcp(1)
