PING(1M) PING(1M)
NAME
ping - send ICMP ECHO_REQUEST packets to network hosts
SYNOPSIS
/usr/etc/ping [-dDfLnoPqQrRv] [-c count] [-s size]
[-i interval] [-l preload] [-p pattern] [-T ttl]
[-t tos] [-w maxwait]
[-I ifaddr] [-g gateway] [-h host] host
DESCRIPTION
Ping is a tool for network testing, measurement and management. It
utilizes the ICMP protocol's 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 an 8-byte timestamp, and then an
arbitrary number of ``pad'' bytes used to fill out the packet.
The host can be the name of a host or its Internet address. The options
are:
-c count
Stop after sending (and waiting the specified delay to receive)
count ECHO_RESPONSE packets.
-d Set the SO_DEBUG option on the socket being used.
-D Set the Don't Fragment bit in the IP header. This can be used to
determine the path MTU.
-f Flood ping. Send ECHO_REQUEST packets as fast as they are answered
with ECHO_RESPONSE packets or one hundred times per second,
whichever is more. (The repetition rate can be adjusted with the -i
option.) 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. This can be
extremely stressful on a network and should be used with caution.
-g gateway
Use Loose Source Routing to send the ECHO_REQUEST packets via
gateway.
-h host
is an alternate way of specifying the target host instead of as the
last argument.
-i interval
Wait interval seconds between sending each packet. The default is
to wait for one second between each packet, except when the -f
option is used when the default is "0.01" second or 10 milliseconds.
-I interface
Send multicast datagrams via the network interface specified by the
interface's hostname or IP address. Send non-multicast datagrams
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with the specified source address.
-l count
Preload the network by sending count packets as fast as possible
before falling into the normal mode of behavior.
-L When sending to a multicast destination address, don't loop the
datagram back to ourselves.
-n Numeric output only. No attempt will be made to look up symbolic
names for host addresses. This is useful to avoid waiting to
convert the addresses of distant hosts to names.
-o Exit successfully after receiving one reply packet.
-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.
-P Use a psuedo-random sequence for the data instead of the default,
fixed sequence of incrementing 8-bit integers. This is useful to
foil compression on PPP and other links.
-q Quiet output. Nothing is displayed except the summary line on
termination.
-Q Do not display responses such as Network Unreachable ICMP messages
concerning the ECHO_REQUESTs sent.
-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(1M)).
-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 eight such routes, and only
six when using the -g option. Many hosts ignore or discard this
option.
-s size
Send datagrams containing size bytes of data. The default is 56,
which translates into 64 ICMP data bytes when combined with the 8
bytes of ICMP header data. The maximum allowed value is 61396.
-t tos
Use the specified hexadecimal type of service.
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-T ttl
Changes the default time-to-live.
-v Verbosely list ICMP packets other than ECHO_RESPONSE that are
received by the system. By default, only ICMP packets (including
ECHO_RESPONSEs) concerning the ECHO_REQUEST packets sent by ping are
listed. When verbosity is turned on, almost all ICMP packets are
listed, including error messages concerning other network traffic.
-w maxwait
Specifies the number of seconds to wait for a response to a packet
before transmitting the next one. The default is 10.0.
Ping should be used primarily for manual fault isolation. Because of the
load it can impose on the network, it is unwise to use ping during normal
operations or from automated scripts. 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''.
Ping repeated sends individual datagrams (by default one per second), and
prints one line of output for every ECHO_RESPONSE returned.
On a trusted system with IP Security Options enabled, if the network
idiom is not MONO, ping also prints a second line containing the
hexadecimal representation of the IP security option in the
ECHO_RESPONSE.
If the -c count option is given, only that number of requests is sent.
If there is no response, then no output other than the final summary is
produced 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. When
the specified number of packets have been sent (and received) or if the
program is terminated with an interrupt (SIGINT), a brief summary is
displayed. When not using the -f (flood) option, the first interrupt,
usually generated by control-C or DEL, causes ping to wait for its
outstanding requests to return. It will wait no longer than the longest
round trip time encountered by previous, successful pings. The second
interrupt stops ping immediately.
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
arbitrary amount of data. When a packetsize is given, it 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).
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If the data space is at least eight bytes large, ping uses the first
eight bytes of this space to include a timestamp to compute round trip
times. If less than eight bytes of pad are specified, no round trip
times are given.
DUPLICATE AND DAMAGED PACKETS
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).
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 maximum possible value of this field is 255, and most Unix systems
set the TTL field of ICMP ECHO_REQUEST packets to 255.
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.
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⊕ Set it to 255; this is what IRIX and 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.
EXIT STATUS
Ping returns 0 on success (the host is alive), and non-zero if the
arguments are incorrect or the host is not responding.
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 record-route option does not work with many hosts and routers.
SEE ALSO
netstat(1), ifconfig(1M), routed(1M)
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