ping, ping6
— send ICMP ECHO_REQUEST packets
to network hosts
ping |
[-DdEefgHLnqRv] [-c
count] [-I
sourceaddr] [-i
interval] [-l
preload] [-p
pattern] [-s
packetsize] [-T
toskeyword] [-t
ttl] [-V
rtable] [-w
maxwait] host |
ping6 |
[-DdEefgHLmnqv] [-c
count] [-h
hoplimit] [-I
sourceaddr] [-i
interval] [-l
preload] [-p
pattern] [-s
packetsize] [-T
toskeyword] [-V
rtable] [-w
maxwait] host |
ping uses the ICMP protocol's mandatory
ECHO_REQUEST datagram to elicit an ICMP
ECHO_REPLY from a host or gateway. These 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 sending after count
ECHO_REQUEST packets have been sent. If
count is 0, send an unlimited number of
packets.
-D- Don't fragment IP packets.
-d- Set the
SO_DEBUG option on the socket being used.
This option has no effect on OpenBSD.
-E- Emit an audible beep (by sending an ASCII BEL character to the standard
error output) 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. This option is
disabled for flood pings.
-e- Emit an audible beep (by sending an ASCII BEL character to the standard
error output) after each non-duplicate response is received. This option
is disabled for flood pings.
-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 network and should be used
with caution.
-g- Provides a visual display of packets received and lost. For every
ECHO_REPLY received, an exclamation mark
‘!’ is printed, while for every missed packet a period
‘.’ is printed. Duplicate and truncated replies are
indicated with ‘D’ and ‘T’ respectively.
-H- Try reverse lookups for addresses.
-h
hoplimit- (IPv6 only) Set the hoplimit.
-I
sourceaddr- Set the source address to transmit from, which is useful on machines with
multiple interfaces. For unicast and multicast pings.
-i
interval- Send one packet every interval seconds. The default
is one second. The interval may contain a fractional
portion. Only the superuser may specify a value less than one second. This
option is incompatible with the
-f option.
-L- Disable the loopback, so the transmitting host doesn't see the ICMP
requests. For multicast pings.
-l
preload- Send preload packets as fast as possible before
reverting to normal behavior. Only root may set a preload value.
-m- (IPv6 only) Do not fragment unicast packets to fit the minimum IPv6 MTU.
If specified twice, do this for multicast packets as well.
-n- Numeric output only. No attempt will be made to look up symbolic names
from addresses in the reply.
-p
pattern- Specify up to 16 pad bytes to fill out the packet sent. This is useful for
diagnosing data-dependent problems in a network. For example, "-p
ff" causes 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- (IPv4 only) 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.
-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. The maximum packet size is 65467 for IPv4 and 65527 for
IPv6.
-T
toskeyword- Change the IPv4 TOS or IPv6 Traffic Class value.
toskeyword may be one of
critical, inetcontrol,
lowdelay, netcontrol,
throughput, reliability,
or one of the DiffServ Code Points: ef,
af11 ... af43, cs0 ...
cs7; or a number in either hex or decimal.
-t
ttl- (IPv4 only) Use the specified time-to-live.
-V
rtable- Set the routing table to be used for outgoing packets.
-v- Verbose output. ICMP packets other than
ECHO_REPLY
that are received are listed.
-w
maxwait- Specify the maximum number of seconds to wait for responses after the last
request has been sent. The default is 10.
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 24 bytes,
ping uses the first sixteen bytes of this space to
include a timestamp which it uses in the computation of round trip times.
The following 8 bytes store a message authentication code. If less than 24
bytes of pad are specified, no round trip times are given.
ping will report duplicate and damaged
packets. Duplicate packets should never occur, 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.
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).
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
(4.3BSD 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:
- 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.
- 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.
- 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.
ping exits 0 if at least one reply is
received, and >0 if no reply is received or an error occurred.
The ping command appeared in
4.3BSD. The ping6 command
was originally a separate program and first appeared in the WIDE Hydrangea
IPv6 protocol stack kit.
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.