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PING(8) BSD System Manager's Manual PING(8)
NAME
ping -- send ICMP ECHO_REQUEST packets to network hosts
SYNOPSIS
ping [-AaDdfnoQqRrv] [-c count] [-G sweepmaxsize] [-g sweepminsize] [-h sweepincrsize]
[-i wait] [-l preload] [-M mask | time] [-m ttl] [-P policy] [-p pattern] [-S src_addr]
[-s packetsize] [-t timeout] [-W waittime] [-z tos] host
ping [-AaDdfLnoQqRrv] [-c count] [-I iface] [-i wait] [-l preload] [-M mask | time] [-m ttl]
[-P policy] [-p pattern] [-S src_addr] [-s packetsize] [-T ttl] [-t timeout]
[-W waittime] [-z tos] mcast-group
DESCRIPTION
The ping utility uses the ICMP protocol's mandatory ECHO_REQUEST datagram to elicit an ICMP
ECHO_RESPONSE 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:
-A Audible. Output a bell (ASCII 0x07) character when no packet is received before the
next packet is transmitted. To cater for round-trip times that are longer than the
interval between transmissions, further missing packets cause a bell only if the
maximum number of unreceived packets has increased.
-a Audible. Include a bell (ASCII 0x07) character in the output when any packet is
received. This option is ignored if other format options are present.
-c count
Stop after sending (and receiving) count ECHO_RESPONSE packets. If this option is
not specified, ping will operate until interrupted. If this option is specified in
conjunction with ping sweeps, each sweep will consist of count 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 sec-
ond, 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 super-user may use this
option. This can be very hard on a network and should be used with caution.
-G sweepmaxsize
Specify the maximum size of ICMP payload when sending sweeping pings. This option
is required for ping sweeps.
-g sweepminsize
Specify the size of ICMP payload to start with when sending sweeping pings. The
default value is 0.
-h sweepincrsize
Specify the number of bytes to increment the size of ICMP payload after each sweep
when sending sweeping pings. The default value is 1.
-I iface
Source multicast packets with the given interface address. This flag only applies
if the ping destination is a multicast address.
-i wait
Wait wait seconds between sending each packet. The default is to wait for one sec-
ond between each packet. The wait time may be fractional, but only the super-user
may specify values less than 1 second. This option is incompatible with the -f
option.
-L Suppress loopback of multicast packets. This flag only applies if the ping destina-
tion is a multicast address.
-l preload
If preload is specified, ping sends that many packets as fast as possible before
falling into its normal mode of behavior. Only the super-user may use this option.
-M mask | time
Use ICMP_MASKREQ or ICMP_TSTAMP instead of ICMP_ECHO. For mask, print the netmask
of the remote machine. Set the net.inet.icmp.maskrepl MIB variable to enable
ICMP_MASKREPLY. For time, print the origination, reception and transmission time-
stamps.
-m ttl Set the IP Time To Live for outgoing packets. If not specified, the kernel uses the
value of the net.inet.ip.ttl MIB variable.
-n Numeric output only. No attempt will be made to lookup symbolic names for host
addresses.
-o Exit successfully after receiving one reply packet.
-P policy
policy specifies IPsec policy for the ping session. For details please refer to
ipsec(4) and ipsec_set_policy(3).
-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 Somewhat quiet output. Don't display ICMP error messages that are in response to
our query messages. Originally, the -v flag was required to display such errors,
but -v displays all ICMP error messages. On a busy machine, this output can be
overbearing. Without the -Q flag, ping prints out any ICMP error messages caused by
its own ECHO_REQUEST messages.
-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 dis-
plays the route buffer on returned packets. Note that the IP header is only large
enough for nine such routes; the traceroute(8) command is usually better at deter-
mining the route packets take to a particular destination. 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 the
RECORD_ROUTE 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 src_addr
Use the following IP address as the source address in outgoing packets. On hosts
with more than one IP address, this option can be used to force the source address
to be something other than the IP address of the interface the probe packet is sent
on. If the IP address is not one of this machine's interface addresses, an error is
returned and nothing is sent.
-s packetsize
Specify 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. Only
the super-user may specify values more than default. This option cannot be used
with ping sweeps.
-T ttl Set the IP Time To Live for multicasted packets. This flag only applies if the ping
destination is a multicast address.
-t timeout
Specify a timeout, in seconds, before ping exits regardless of how many packets have
been received.
-v Verbose output. ICMP packets other than ECHO_RESPONSE that are received are listed.
-W waittime
Time in milliseconds to wait for a reply for each packet sent. If a reply arrives
later, the packet is not printed as replied, but considered as replied when calcu-
lating statistics.
-z tos Use the specified type of service.
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 com-
puted. If duplicate packets are received, they are not included in the packet loss calcula-
tion, although the round trip time of these packets is used in calculating the round-trip
time statistics. 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, showing the number of
packets sent and received, and the minimum, mean, maximum, and standard deviation of the
round-trip times.
If ping receives a SIGINFO (see the status argument for stty(1)) signal, the current number
of packets sent and received, and the minimum, mean, and maximum of the round-trip times
will be written to the standard error output.
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.
ICMP PACKET DETAILS
An IP header without options is 20 bytes. An ICMP ECHO_REQUEST packet contains an addi-
tional 8 bytes worth of ICMP header followed by an arbitrary amount of data. When a
packetsize is given, this indicated 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
The ping utility will report duplicate and damaged packets. Duplicate packets should never
occur when pinging a unicast address, and seem to be caused by inappropriate link-level
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.
Duplicates are expected when pinging a broadcast or multicast address, since they are not
really duplicates but replies from different hosts to the same request.
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
The (inter)network layer should never treat packets differently depending on the data con-
tained 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 does not have sufficient ``transitions'',
such as all ones or all zeros, or a pattern right at the edge, such as almost all zeros. It
is not necessarily enough to specify a data pattern of all zeros (for example) on the com-
mand line because the pattern that is of interest is at the data link level, and the rela-
tionship 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 cannot 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.
TTL DETAILS
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 recommends setting the TTL field for IP packets to 64, but many
systems use smaller values (4.3BSD uses 30, 4.2BSD 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 BSD 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 BSD 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 sys-
tem 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 val-
ues.
EXIT STATUS
The ping utility exits with one of the following values:
0 At least one response was heard from the specified host.
2 The transmission was successful but no responses were received.
any other value
An error occurred. These values are defined in <sysexits.h>.
SEE ALSO
netstat(1), ifconfig(8), routed(8), traceroute(8)
HISTORY
The ping utility appeared in 4.3BSD.
AUTHORS
The original ping utility was written by Mike Muuss while at the US Army Ballistics Research
Laboratory.
BUGS
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.
The -v option is not worth much on busy hosts.
BSD April 4, 2006 BSD |
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