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NAME    [Toc]    [Back]

     ping -- send ICMP ECHO_REQUEST packets to network hosts

SYNOPSIS    [Toc]    [Back]

     ping [-AaDdfnoQqRrv] [-c count] [-i wait] [-l preload] [-M mask | time]
	  [-m ttl] [-P policy] [-p pattern] [-S src_addr] [-s packetsize]
	  [-t timeout] [-z tos] host
     ping [-AaDdfLnoQqRrv] [-c count] [-I iface] [-i wait] [-l preload]
	  [-M mask | time] [-m ttl] [-P policy] [-p pattern] [-S src_addr]
	  [-s packetsize] [-T ttl] [-t timeout] [-z tos] mcast-group

DESCRIPTION    [Toc]    [Back]

     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.  The options are as follows:

     -A      Audible.  Output a bell (ASCII 0x07) character 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.

     -a      Audible.  Include a bell (ASCII 0x07) character in the output
	     when any packet is received.  This option is ignored if other
	     format options are present.

     -c count
	     Stop after sending (and receiving) count ECHO_RESPONSE packets.
	     If this option is not specified, ping will operate until interrupted.

     -D      Set the Don't Fragment bit.

     -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
	     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
	     super-user may use this option.  This can be very hard on a net-
	     work and should be used with caution.

     -I iface
	     Source multicast packets with the given interface address.  This
	     flag only applies if the ping destination is a multicast address.

     -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 super-user may specify values less than
	     1 second.	This option is incompatible with the -f option.

     -L      Suppress loopback of multicast packets.  This flag only applies
	     if the ping destination is a multicast address.

     -l preload
	     If preload is specified, ping sends that many packets as fast as
	     possible before falling into its normal mode of behavior.	Only
	     the super-user may use this option.

     -M mask | time
	     Use ICMP_MASKREQ or ICMP_TSTAMP instead of ICMP_ECHO.  For mask,
	     print the netmask of the remote machine.  Set the
	     net.inet.icmp.maskrepl MIB variable to enable ICMP_MASKREPLY.
	     For time, print the origination, reception and transmission timestamps.

     -m ttl  Set the IP Time To Live for outgoing packets.  If not specified,
	     the kernel uses the value of the net.inet.ip.ttl MIB variable.

     -n      Numeric output only.  No attempt will be made to lookup symbolic
	     names for host addresses.

     -o      Exit successfully after receiving one reply packet.

     -P policy
	     policy specifies IPsec policy for the ping session.  For details
	     please refer to ipsec(4) and ipsec_set_policy(3).

     -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      Somewhat quiet output.  Don't display ICMP error messages that
	     are in response to our query messages.  Originally, the -v flag
	     was required to display such errors, but -v displays all ICMP
	     error messages.  On a busy machine, this output can be overbearing.
  Without the -Q flag, ping prints out any ICMP error messages
 caused by its own ECHO_REQUEST messages.

     -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; the traceroute(8) command is usually better at
	     determining the route packets take to a particular destination.
	     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 the
	     RECORD_ROUTE 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 src_addr
	     Use the following IP address as the source address in outgoing
	     packets.  On hosts with more than one IP address, this option can
	     be used to force the source address to be something other than
	     the IP address of the interface the probe packet is sent on.  If
	     the IP address is not one of this machine's interface addresses,
	     an error is returned and nothing is sent.

     -s packetsize
	     Specify 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.  Only the super-user may specify values
 more than default.

     -T ttl  Set the IP Time To Live for multicasted packets.  This flag only
	     applies if the ping destination is a multicast address.

     -t timeout
	     Specify a timeout, in seconds, before ping exits regardless of
	     how many packets have been received.

     -v      Verbose output.  ICMP packets other than ECHO_RESPONSE that are
	     received are listed.

     -z tos  Use the specified type of service.

     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 round-trip time statistics.  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, showing the number of packets sent
     and received, and the minimum, mean, maximum, and standard deviation of
     the round-trip times.

     If ping receives a SIGINFO (see the status argument for stty(1)) signal,
     the current number of packets sent and received, and the minimum, mean,
     and maximum of the round-trip times will be written to the standard error

     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    [Toc]    [Back]

     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 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.


     The ping utility will report duplicate and damaged packets.  Duplicate
     packets should never occur when pinging a unicast address, 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.
     Duplicates are expected when pinging a broadcast or multicast address,
     since they are not really duplicates but replies from different hosts to
     the same request.

     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).


     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 ones or all zeros, or a pattern right at the edge, such as
     almost all zeros.	It is not 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 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.

TTL DETAILS    [Toc]    [Back]

     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 recommends setting the TTL field for IP packets
     to 64, but many systems use smaller values (4.3BSD uses 30, 4.2BSD used

     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 BSD 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 BSD 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.

RETURN VALUES    [Toc]    [Back]

     The ping utility returns an exit status of zero if at least one response
     was heard from the specified host; a status of two if the transmission
     was successful but no responses were received; or another value (from
     <sysexits.h>) if an error occurred.

SEE ALSO    [Toc]    [Back]

     netstat(1), ifconfig(8), routed(8), traceroute(8)

HISTORY    [Toc]    [Back]

     The ping utility appeared in 4.3BSD.

AUTHORS    [Toc]    [Back]

     The original ping utility was written by Mike Muuss while at the US Army
     Ballistics Research Laboratory.

BUGS    [Toc]    [Back]

     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,

     Flood pinging is not recommended in general, and flood pinging the broadcast
 address should only be done under very controlled conditions.

     The -v option is not worth much on busy hosts.

FreeBSD 5.2.1			October 2, 2002 		 FreeBSD 5.2.1
[ Back ]
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