ping - send ICMP ECHO_REQUEST packets to network hosts
ping [-DdfLnqRrv] [-c count] [-I ifaddr] [-i wait] [-l
preload]
[-p pattern] [-s packetsize] [-T tos] [-t ttl] [-w
maxwait] host
ping uses the ICMP protocol's mandatory ECHO_REQUEST datagram to elicit
an ICMP ECHO_REPLY from a host or gateway. ECHO_REQUEST
datagrams
(``pings'') have an IP and ICMP header, followed by a
``struct timeval''
and then an arbitrary number of ``pad'' bytes used to fill
out the packet.
The options are as follows:
-c count
Stop after sending count ECHO_REQUEST packets.
-D Set the Don't Fragment bit.
-d Set the SO_DEBUG option on the socket being used.
-f Flood ping. Outputs packets as fast as they come
back or one
hundred times per second, whichever is more. For
every
ECHO_REQUEST sent a period ``.'' is printed, while
for every
ECHO_REPLY received a backspace is printed. This
provides a
rapid display of how many packets are being dropped.
Only the
superuser may use this option. This can be very
hard on a net-
work and should be used with caution.
-I ifaddr
Specify the interface to transmit from on machines
with multiple
interfaces. For unicast and multicast pings.
-i wait
Wait wait seconds between sending each packet. The
default is to
wait for one second between each packet. The wait
time may be
fractional, but only the superuser may specify a
value less than
one second. This option is incompatible with the -f
option.
-l preload
If preload is specified, ping sends that many packets as fast as
possible before falling into its normal mode of behavior. Only
root may set a preload value.
-n Numeric output only. No attempt will be made to
look up symbolic
names for host addresses.
-p pattern
You may specify up to 16 ``pad'' bytes to fill out
the packet you
send. This is useful for diagnosing data-dependent
problems in a
network. For example, ``-p ff'' will cause the sent
packet to be
filled with all ones.
-q Quiet output. Nothing is displayed except the summary lines at
startup time and when finished.
-R Record route. Includes the RECORD_ROUTE option in
the
ECHO_REQUEST packet and displays the route buffer on
returned
packets. Note that the IP header is only large
enough for nine
such routes. If more routes come back than should,
such as due
to an illegal spoofed packet, ping will print the
route list and
then truncate it at the correct spot. Many hosts
ignore or discard
this option.
-r Bypass the normal routing tables and send directly
to a host on
an attached network. If the host is not on a directly attached
network, an error is returned. This option can be
used to ping a
local host through an interface that has no route
through it
(e.g., after the interface was dropped by routed(8)).
-s packetsize
Specifies the number of data bytes to be sent. The
default is
56, which translates into 64 ICMP data bytes when
combined with
the 8 bytes of ICMP header data. If the -D or -T
options are
specified, or the -t option to a unicast destination, a raw socket
will be used and the 8 bytes of header data are
included in
packetsize.
-T tos Use the specified type of service.
-t ttl Use the specified time-to-live.
-v Verbose output. ICMP packets other than ECHO_REPLY
that are received
are listed.
-w maxwait
Specifies the maximum number of seconds to wait for
a response to
a packet before transmitting the next one. The default is 10.
In addition, the following option may be used for multicast
pings:
-L Disable the loopback, so the transmitting host
doesn't see the
ICMP requests.
When using ping for fault isolation, it should first be run
on the local
host to verify that the local network interface is up and
running. Then,
hosts and gateways further and further away should be
``pinged''.
Round trip times and packet loss statistics are computed.
If duplicate
packets are received, they are not included in the packet
loss calculation,
although the round trip time of these packets is used
in calculating
the minimum/average/maximum round trip time numbers and
the standard
deviation.
When the specified number of packets have been sent (and received), or if
the program is terminated with a SIGINT, a brief summary is
displayed.
The summary information can also be displayed while ping is
running by
sending it a SIGINFO signal (see the status argument of
stty(1) for more
information).
This program is intended for use in network testing, measurement and management.
Because of the load it can impose on the network,
it is unwise
to use ping during normal operations or from automated
scripts.
An IP header without options is 20 bytes. An ICMP ECHO_REQUEST packet
contains an additional 8 bytes worth of ICMP header followed
by an arbitrary
amount of data. When a packetsize is given, this indicates the
size of this extra piece of data (the default is 56). Thus
the amount of
data received inside of an IP packet of type ICMP ECHO_REPLY
will always
be 8 bytes more than the requested data space (the ICMP
header).
If the data space is at least eight bytes large, ping uses
the first
eight bytes of this space to include a timestamp which it
uses in the
computation of round trip times. If less than eight bytes
of pad are
specified, no round trip times are given.
DUPLICATE AND DAMAGED PACKETS [Toc] [Back] ping will report duplicate and damaged packets. Duplicate
packets should
never occur, and seem to be caused by inappropriate linklevel retransmissions.
Duplicates may occur in many situations and are
rarely (if ever)
a good sign, although the presence of low levels of duplicates may
not always be cause for alarm.
Damaged packets are obviously serious cause for alarm and
often indicate
broken hardware somewhere in the ping packet's path (in the
network or in
the hosts).
TRYING DIFFERENT DATA PATTERNS [Toc] [Back] The (inter)network layer should never treat packets differently depending
on the data contained in the data portion. Unfortunately,
data-dependent
problems have been known to sneak into networks and remain
undetected for
long periods of time. In many cases the particular pattern
that will
have problems is something that doesn't have sufficient
``transitions'',
such as all ones or all zeros, or a pattern right at the
edge, such as
almost all zeros. It isn't necessarily enough to specify a
data pattern
of all zeros (for example) on the command line because the
pattern that
is of interest is at the data link level, and the relationship between
what you type and what the controllers transmit can be complicated.
This means that if you have a data-dependent problem you
will probably
have to do a lot of testing to find it. If you are lucky,
you may manage
to find a file that either can't be sent across your network
or that
takes much longer to transfer than other similar length
files. You can
then examine this file for repeated patterns that you can
test using the
-p option of ping.
The TTL value of an IP packet represents the maximum number
of IP routers
that the packet can go through before being thrown away. In
current
practice you can expect each router in the Internet to
decrement the TTL
field by exactly one.
The TCP/IP specification states that the TTL field for TCP
packets should
be set to 60, but many systems use smaller values (4.3 BSD
uses 30, 4.2
used 15).
The maximum possible value of this field is 255, and most
Unix systems
set the TTL field of ICMP ECHO_REQUEST packets to 255. This
is why you
will find you can ``ping'' some hosts, but not reach them
with telnet(1)
or ftp(1).
In normal operation, ping prints the TTL value from the
packet it receives.
When a remote system receives a ping packet, it can
do one of
three things with the TTL field in its response:
+o Not change it; this is what Berkeley Unix systems did
before the
4.3BSD-Tahoe release. In this case the TTL value in the
received
packet will be 255 minus the number of routers in the
round trip
path.
+o Set it to 255; this is what current Berkeley Unix systems do. In
this case the TTL value in the received packet will be
255 minus the
number of routers in the path from the remote system to
the pinging
host.
+o Set it to some other value. Some machines use the same
value for
ICMP packets that they use for TCP packets, for example
either 30 or
60. Others may use completely wild values.
netstat(1), ifconfig(8), routed(8), spray(8)
The ping command appeared in 4.3BSD.
Many hosts and gateways ignore the RECORD_ROUTE option.
The maximum IP header length is too small for options like
RECORD_ROUTE
to be completely useful. There's not much that can be done
about this,
however.
Flood pinging is not recommended in general, and flood pinging the broadcast
address should only be done under very controlled conditions.
OpenBSD 3.6 December 11, 1993
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