ping



PING(8)                     System Manager's Manual                    PING(8)


NAME

     ping - send ICMP ECHO_REQUEST packets to network hosts


SYNOPSIS

     ping [-DdEefLnqRv] [-c count] [-I ifaddr] [-i wait] [-l preload]
          [-p pattern] [-s packetsize] [-T toskeyword] [-t ttl] [-V rtable]
          [-w maxwait] host


DESCRIPTION

     ping uses the ICMP protocol's mandatory ECHO_REQUEST datagram to elicit
     an ICMP ECHO_REPLY 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.  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      Set the Don't Fragment bit.

     -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.

     -I ifaddr
             Specify the interface address to transmit from on machines with
             multiple interfaces.  For unicast and multicast pings.

     -i wait
             Wait wait seconds between sending each packet.  The default is to
             wait for one second between each packet.  The wait time may be
             fractional, but 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
             If preload is specified, ping sends that many packets as fast as
             possible before falling into its normal mode of behavior.  Only
             root may set a preload value.

     -n      Numeric output only.  No attempt will be made to look up 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 output.  Nothing is displayed except the summary lines at
             startup time and when finished.

     -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 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
             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 toskeyword
             Change IPv4 TOS 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  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
             Specifies 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.


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 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.


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 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:

     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.


EXIT STATUS

     ping exits 0 if at least one reply is received, and >0 if no reply is
     received or an error occurred.


SEE ALSO

     netstat(1), ifconfig(8), ping6(8)


HISTORY

     The ping command appeared in 4.3BSD.


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.

OpenBSD 5.9                     March 24, 2014                     OpenBSD 5.9

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