Man page of ping
Section: Maintenance Commands (8)
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ping - Sends ICMP ECHO_REQUEST packets to network hosts
/usr/sbin/ping [-dfnqruvR] [-c count] [-i wait] [-l preload] [-p pattern] [-s packetsize] host
Stops after sending (and receiving) count ECHO_RESPONSE packets.
Set the SO_DEBUG option on the socket being used.
Floods ping. Outputs packets as fast as they come back or
100 times per second, whichever is more.
For every ECHO_REQUEST sent, a . (dot) is printed, while for every
ECHO_REPLY received a backspace is used.
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 (see Cautions).
Waits wait seconds between sending each packet.
The default is to wait for 1 second between each packet.
This option is incompatible with the -f option.
If preload is specified, ping
sends that many packets as fast as possible before falling into its normal
mode of behavior. Only the superuser may use this option. This can be very
hard on a network and should be used with caution (see Cautions).
Numeric output only. No attempt will be made to look up symbolic names for
host addresses. This occurs only when displaying ICMP packets other than
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
Quiets output. Nothing is displayed except the summary lines at
start-up time and when finished.
Records 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.
Many hosts ignore or discard this option.
Bypasses the normal routing tables and directly sends 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 send ping to a local
through an interface that has no route
through it (for example, after the interface was dropped by routed).
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.
Displays the time in microseconds (three decimal places).
In order to ensure this microsecond precision, the NTP_TIME
and MICRO_TIME kernel options must be on. By default NTP_TIME and
MICRO_TIME kernel options are off. If these kernel options are off and
this flag is used, the time is displayed to three decimal places, but
Specifies verbose output. ICMP packets other than ECHO_RESPONSE that
are received are listed.
The ping command uses the ICMP (Internet Control
Message Protocol) protocol's mandatory ECHO_REQUEST
datagram to elicit an ICMP ECHO_RESPONSE from the specified
host or gateway host, where host is a network
name or IP address. ECHO_REQUEST datagrams (pings) have an IP
(Internet Protocol) and ICMP header, followed by a
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 sent
the ping command. Round-trip times and packet loss
statistics are computed. If duplicate packets
are received, they are not included in the packet
loss calculations, although the round-trip time
of these packets is used in calculating the minimum,
average, and maximum round-trip time numbers. When the specified
number of packets have been sent (and received) or if the program
is terminated with a SIGINT, a brief summary
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 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 8 bytes large, ping
uses the first 8 bytes of this space to include a timestamp, which
it uses in the computation of round-trip times.
If less than 8 bytes of pad are specified, no round-trip times are
Duplicate and Damaged Packets
command 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 does not have sufficient transitions, such as all 1s (ones) or
all 0s (zeros), or a pattern right at the edge, such as almost all 0s
(zeros). It is not necessarily enough to specify
a data pattern of all 0s (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 enter 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.
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 1 (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
compatible systems set
the TTL field of ICMP ECHO_REQUEST packets to 255.
This is why you will find you can use the ping
command on some hosts, but not reach them
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 compatible systems
did before the 4.3BSD 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 compatible
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 host that received the ping command.
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.
Many hosts and gateways ignore the RECORD_ROUTE option.
Flooding and preloading the ping command is not recommended in general,
and flooding ping on the broadcast address should only be done under
very controlled conditions.
Specifies the command path
Commands: netstat(1), ifconfig(8)
Daemons: gated(8), routed(8)
- ICMP Packet Details
- Duplicate and Damaged Packets
- Trying Different Data Patterns
- TTL Details
- RELATED INFORMATION
This document was created by
using the manual pages.
Time: 02:40:31 GMT, October 02, 2010