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

NAME
     ping -- send ICMP ECHO_REQUEST packets to network hosts

SYNOPSIS
     ping [-AQRadfnqrv]	[-c count] [-i wait] [-l preload] [-m ttl]
	  [-p pattern] [-P policy] [-s packetsize] [-S src_addr] [-t timeout]
	  [host	| [-L] [-I interface] [-T ttl] mcast-group]

DESCRIPTION
     Ping 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	trans-
	     missions, further missing packets cause a bell only if the	maxi-
	     mum 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 inter-
	     rupted.

     -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	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.

     -I	interface
	     Source multicast packets with the given interface address.	 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	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.

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

     -n	     Numeric output only.  No attempt will be made to lookup 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.

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

     -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 overbear-
	     ing.  Without the -Q flag,	ping prints out	any ICMP error mes-
	     sages 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	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 use this
	     option.

     -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.

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

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

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

     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 calcula-
     tion, although the	round trip time	of these packets is used in calculat-
     ing 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
     output.

     This program is intended for use in network testing, measurement and man-
     agement.  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	arbi-
     trary 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.

DUPLICATE AND DAMAGED PACKETS
     Ping 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).

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 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
     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 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
     The ping command 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
     netstat(1), ifconfig(8), routed(8), traceroute(8)

HISTORY
     The ping command appeared in 4.3BSD.

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

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	broad-
     cast address should only be done under very controlled conditions.

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

FreeBSD	9.3		      September	25, 2001		   FreeBSD 9.3

NAME | SYNOPSIS | DESCRIPTION | ICMP PACKET DETAILS | DUPLICATE AND DAMAGED PACKETS | TRYING DIFFERENT DATA PATTERNS | TTL DETAILS | RETURN VALUES | SEE ALSO | HISTORY | AUTHORS | BUGS

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