PING(1) BSD Reference Manual PING(1)NAMEping - send query packets to network hosts
SYNOPSISping [-dfnqRrv] [-a address_family] [-c count] [-i wait] [-l preload] [-p
pattern] [-s packetsize] host
DESCRIPTION
The ping utility sends a packet to the specified host and waits for a re-
ply. The host address and round-trip times for each pair of packets are
displayed. In addition, the total number of packets sent, received, per-
cent packet loss and minimum, average and maximum round-trip times are
displayed when the program exits or when a SIGINFO signal (see the
``status'' argument for stty(1)) is received.
The options are as follows:
-A ah_level
Set the IPSEC authentication level to ah_level. Valid values are:
``1'' (IPSEC_LEVEL_USE), ``2'' (IPSEC_LEVEL_REQUIRE) and ``3''
(IPSEC_LEVEL_UNIQUE). See ipsec(4).
-a address_family
Select the address family to use. ( ``inet'' or ``inet6'' ).
This is very important because ping uses a raw socket to send
ICMP (or ICMPv6) echo replies to the requested destination.
-c count
Stop after sending (and receiving) count packets. After count
packets have been sent, ping will wait no more than twice the
round-trip time of the last received packet (or 10 seconds if no
packets have been received) before exiting.
-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 query
packet sent a period ``.'' is printed, and for every response
packet 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.
-i wait
Pause wait seconds between sending each query packet. By de-
fault, ping waits one second between each packet.
-l preload
If preload is specified, ping sends that many packets as fast as
possible before continuing in its normal mode.
-N esptun_level
Set the IPSEC ESP tunnel mode encryption level to esptun_level.
Currently, the only valid value is: ``1'' (IPSEC_LEVEL_USE). See
ipsec(4).
-n Numeric output only. No attempt will be made to lookup 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 mode. Nothing is displayed except the summary lines at
startup time and when ping exits.
-R Record route. Includes the RECORD_ROUTE option in the query
packet and displays the route buffer on returned packets. Note
that the IP header is only large enough for nine such routes, and
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.
-T esptrans_level
Set the IPSEC ESP transport mode encryption level to
esptrans_level. Valid values are: ``1'' (IPSEC_LEVEL_USE), ``2''
(IPSEC_LEVEL_REQUIRE) and ``3'' (IPSEC_LEVEL_UNIQUE). See
ipsec(4).
-v Verbose output. This option causes ping to list ICMP packets
other than ECHO_RESPONSE that are received.
The ping utility exits 0 on success, and >0 if an error occurs or if no
response was received from the target system.
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.
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 calcula-
tion, although the round trip time of these packets is used in calculat-
ing the minimum/average/maximum round-trip time numbers. When the speci-
fied number of packets have been sent (and received) or if the program is
terminated with a SIGINT signal, or the program receives a SIGINFO sig-
nal, a brief summary is displayed.
This program is intended for use in network testing, measurement and man-
agement. Because of the load it can impose on the network, it is unwise
to use ping during normal operations or from automated scripts without
specifying the -c option.
ICMP PACKET DETAILS
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 arbi-
trary 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.
ICMPv6 PACKET DETAILS
ICMPv6 headers are the same size as ICMP headers. IPv6 headers are dou-
ble the size of IP headers. Other than that difference, the details are
the same as ICMP, mentioned above.
DUPLICATE AND DAMAGED PACKETS
Ping will report duplicate and damaged packets. Duplicate packets should
normally never occur, and seem to be caused by inappropriate link-level
retransmissions. In the situations where they do occur, they 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
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.
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 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 re-
ceives. 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.
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 that can be done about
this, however.
Flood pinging is not recommended in general, and flood pinging the broad-
cast address should only be done under very controlled conditions.
If the system security level is set high, ping may send encrypted and/or
authenticated packets unbeknownst to the caller, and may pass up addi-
tional options unexpected.
IPv4-mapped IPv6 address (::FFFF:<v4 address>) will not work with ping.
Unlike IPv4, IPv6 pings have their headers and ICMP checksums determined
in kernel space. This is not so much a bug with ping, as it is an as-
sumption about the underlying kernel on which ping runs.
SEE ALSOnetstat(1), ifconfig(8), routed(8), traceroute(8)HISTORY
The ping command appeared in 4.3BSD.
4.3 Berkeley Distribution April 28, 1995 4