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 contact the nttcp started on the
partner machine and initiate the transfer. On default the
program transfers 2048 buffers of 4KByte length (a total
of 8 MByte) to the partner host. On both sides the perfor
mance will be measured and the findings (both, remote and
local) are reported on the local side. You may change
nearly every parameter of the transmission 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 implemented 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 purposes.
-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 transfered. 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 transmission is via TCP, a
uniq pattern for the whole transmission is gener
ated. 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 num
bered, 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 performance, 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 genera
tor. 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 connec
tions 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 number 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 speci
fied multicast address and port. This option
enforces the -u and-t
switch.AlsoseeMULTICASTlaterinthisdocument.
OUTPUT
The output of the program consists of two lines of num
bers; or more lines if used in transmitting to more than
one machine (multicasting). The first line for the mea
sures 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 similiar 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' respec
tive '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 traffic. 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 compiled with option MROUTING works. But be
aware what this means to your networking environment. Most
ethernet switches for example handle multicast 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 suggested. 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 net
work 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 mea
sures. 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)
