.\" Copyright (c) 1985, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\" %sccs.include.redist.man%
.\" @(#)ping.8 8.2 (Berkeley) %G%
datagrams (``pings'') have an IP and
and then an arbitrary number of ``pad'' bytes used to fill out the
The options are as follows:
Stop after sending (and receiving)
option on the socket being used.
Outputs packets as fast as they come back or one hundred times per second,
sent a period ``.'' is printed, while for every
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.
.Em between sending each packet .
The default is to wait for one second between each packet.
This option is incompatible with the
sends that many packets as fast as possible before falling into its normal
No attempt will be made to lookup symbolic names for host addresses.
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.
will cause the sent packet to be filled with all
Nothing is displayed except the summary lines at startup time and
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.
Bypass the normal routing tables and send directly to a host on an attached
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
Specifies the number of data bytes to be sent.
The default is 56, which translates into 64
that are received are listed.
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.
When the specified number of packets have been sent (and received) or
if the program is terminated with a
a brief summary is displayed.
This program is intended for use in network testing, measurement and
Because of the load it can impose on the network, it is unwise to use
during normal operations or from automated scripts.
An IP header without options is 20 bytes.
packet contains an additional 8 bytes worth
header followed by an arbitrary amount of data.
is given, this indicated the size of this extra piece of data (the
Thus the amount of data received inside of an IP packet of type
will always be 8 bytes more than the requested data space
If the data space is at least eight bytes large,
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
.Sh DUPLICATE AND DAMAGED PACKETS
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
packet's path (in the network or in the hosts).
.Sh 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
You can then examine this file for repeated patterns that you can test
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
specification states that the
be set to 60, but many systems use smaller values (4.3
The maximum possible value of this field is 255, and most Unix systems set
This is why you will find you can ``ping'' 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
Not change it; this is what Berkeley Unix systems did before the
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.
value in the received packet will be 255 minus the
number of routers in the path
Set it to some other value.
Some machines use the same value for
packets that they use for
packets, for example either 30 or 60.
Others may use completely wild values.
Many Hosts and Gateways ignore the
The maximum IP header length is too small for options like
There's not much that 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.