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PING(1M)							      PING(1M)

NAME    [Toc]    [Back]

     ping - send ICMP ECHO_REQUEST packets to network hosts

SYNOPSIS    [Toc]    [Back]

     /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    [Toc]    [Back]

     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

     -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

     -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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PING(1M)							      PING(1M)

	  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

     -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

     -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.

									Page 2

PING(1M)							      PING(1M)

     -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

     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    [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, 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).

									Page 3

PING(1M)							      PING(1M)

     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.


     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).


     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    [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 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:

     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.

									Page 4

PING(1M)							      PING(1M)

     o 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

     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    [Toc]    [Back]

     Ping returns 0 on success (the host is alive), and	non-zero if the
     arguments are incorrect or	the host is not	responding.

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,

     On	a trusted system with IP Security Options enabled the IP header	will
     not be able to accommodate	both the security option and the RECORD_ROUTE
     option.  Other IP options may not be supported if the security option is
     significantly large and in	these situations the use of these options will
     be	refused.

     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    [Toc]    [Back]

     netstat(1), ifconfig(1M), routed(1M)

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