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

NAME
       ping, ping6 - send ICMP ECHO_REQUEST to network hosts

SYNOPSIS
       ping  [-LRUbdfnqrvVaAB] [-c count] [-m mark] [-i interval] [-l preload]
       [-p pattern] [-s packetsize] [-t ttl] [-w deadline] [-F flowlabel]  [-I
       interface]  [-M	hint] [-N nioption] [-Q tos] [-S sndbuf] [-T timestamp
       option] [-W timeout] [hop ...] destination

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.

       ping6 can also send Node Information Queries (RFC4620).

OPTIONS
       -a     Audible ping.

       -A     Adaptive ping. Interpacket interval adapts to  round-trip	 time,
	      so  that	effectively  not more than one (or more, if preload is
	      set) unanswered probes present in the network. Minimal  interval
	      is  200msec  for	not super-user.	 On networks with low rtt this
	      mode is essentially equivalent to flood mode.

       -b     Allow pinging a broadcast address.

       -B     Do not allow ping to  change  source  address  of	 probes.   The
	      address is bound to one selected when ping starts.

       -m mark
	      use  mark to tag the packets going out. This is useful for vari‐
	      ety of reasons within the kernel such as using policy routing to
	      select specific outbound processing.

       -c count
	      Stop  after  sending  count  ECHO_REQUEST packets. With deadline
	      option, ping waits for count ECHO_REPLY packets, until the time‐
	      out expires.

       -d     Set  the SO_DEBUG option on the socket being used.  Essentially,
	      this socket option is not used by Linux kernel.

       -F flow label
	      Allocate and set 20 bit flow  label  on  echo  request  packets.
	      (Only  ping6).  If  value	 is zero, kernel allocates random flow
	      label.

       -f     Flood ping. For  every  ECHO_REQUEST  sent  a  period  ``.''  is
	      printed,	while  for  ever  ECHO_REPLY  received	a backspace is
	      printed.	This provides a rapid display of how many packets  are
	      being  dropped.	If  interval is not given, it sets interval to
	      zero and outputs packets as fast as they come back or  one  hun‐
	      dred  times  per second, whichever is more.  Only the super-user
	      may use this option with zero interval.

       -i interval
	      Wait interval seconds between sending each packet.  The  default
	      is  to  wait for one second between each packet normally, or not
	      to wait in flood mode. Only super-user may set interval to  val‐
	      ues less 0.2 seconds.

       -I interface address
	      Set  source address to specified interface address. Argument may
	      be numeric IP address or name of device. When pinging IPv6 link-
	      local address this option is required.

       -l preload
	      If  preload is specified, ping sends that many packets not wait‐
	      ing for reply.  Only the super-user may select preload more than
	      3.

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

       -N nioption
	      Send ICMPv6 Node Information Queries (RFC4620), instead of  Echo
	      Request.

	      name   Queries for Node Names.

	      ipv6   Queries  for  IPv6 Addresses. There are several IPv6 spe‐
		     cific flags.

		     ipv6-global
			    Request IPv6 global-scope addresses.

		     ipv6-sitelocal
			    Request IPv6 site-local addresses.

		     ipv6-linklocal
			    Request IPv6 link-local addresses.

		     ipv6-all
			    Request IPv6 addresses on other interfaces.

	      ipv4   Queries for IPv4 Addresses.  There is one	IPv4  specific
		     flag.

		     ipv4-all
			    Request IPv4 addresses on other interfaces.

	      subject-ipv6=ipv6addr
		     IPv6 subject address.

	      subject-ipv4=ipv4addr
		     IPv4 subject address.

	      subject-name=nodename
		     Subject  name.   If it contains more than one dot, fully-
		     qualified domain name is assumed.

	      subject-fqdn=nodename
		     Subject name.   Fully-qualified  domain  name  is	always
		     assumed.

       -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.

       -D     Print  timestamp	(unix  time + microseconds as in gettimeofday)
	      before each line.

       -Q tos Set Quality of Service -related bits in ICMP datagrams.  tos can
	      be either decimal or hex number.	Traditionally (RFC1349), these
	      have been interpreted as: 0 for reserved (currently being	 rede‐
	      fined  as	 congestion  control), 1-4 for Type of Service and 5-7
	      for Precedence.  Possible settings for Type of Service are: min‐
	      imal cost: 0x02, reliability: 0x04, throughput: 0x08, low delay:
	      0x10.  Multiple TOS bits should not be set simultaneously.  Pos‐
	      sible settings for special Precedence range from priority (0x20)
	      to net control (0xe0).  You must be root (CAP_NET_ADMIN capabil‐
	      ity) to use Critical or higher precedence value.	You cannot set
	      bit 0x01 (reserved) unless ECN has been enabled in  the  kernel.
	      In RFC2474, these fields has been redefined as 8-bit Differenti‐
	      ated Services (DS), consisting of: bits  0-1  of	separate  data
	      (ECN  will  be  used, here), and bits 2-7 of Differentiated Ser‐
	      vices Codepoint (DSCP).

       -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.  Many hosts ignore or discard this option.

       -r     Bypass the normal routing tables and send directly to a host  on
	      an  attached  interface.	 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 provided the option -I is also used.

       -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.

       -S sndbuf
	      Set socket sndbuf. If not specified, it is  selected  to	buffer
	      not more than one packet.

       -t ttl Set the IP Time to Live.

       -T timestamp option
	      Set  special  IP	timestamp  options.   timestamp	 option may be
	      either  tsonly  (only  timestamps),  tsandaddr  (timestamps  and
	      addresses) or tsprespec host1 [host2 [host3 [host4]]] (timestamp
	      prespecified hops).

       -M hint
	      Select Path MTU Discovery strategy.  hint may be either do (pro‐
	      hibit  fragmentation,  even local one), want (do PMTU discovery,
	      fragment locally when packet size is large), or dont (do not set
	      DF flag).

       -U     Print  full  user-to-user	 latency (the old behaviour). Normally
	      ping prints network round trip time, which can be different f.e.
	      due to DNS failures.

       -v     Verbose output.

       -V     Show version and exit.

       -w deadline
	      Specify  a  timeout, in seconds, before ping exits regardless of
	      how many packets have been sent or received. In this  case  ping
	      does  not	 stop after count packet are sent, it waits either for
	      deadline expire or until count probes are answered or  for  some
	      error notification from network.

       -W timeout
	      Time to wait for a response, in seconds. The option affects only
	      timeout in absense of any responses, otherwise  ping  waits  for
	      two RTTs.

       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  run‐
       ning.  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 SIGINT, a brief summary is dis‐
       played. Shorter current statistics can be obtained without  termination
       of process with signal SIGQUIT.

       If  ping	 does  not  receive any reply packets at all it will exit with
       code 1. If a packet count and deadline are both	specified,  and	 fewer
       than  count  packets are received by the time the deadline has arrived,
       it will also exit with code 1.  On other error it exits	with  code  2.
       Otherwise  it exits with code 0. This makes it possible to use the exit
       code to see if a host is alive or not.

       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  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 of size of struct timeval ping  uses  the
       beginning  bytes	 of this space to include a timestamp which it uses in
       the computation of round trip times.  If the data space is shorter,  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 indi‐
       cate broken hardware somewhere in the ping packet's path (in  the  net‐
       work or in the hosts).

TRYING DIFFERENT DATA PATTERNS
       The (inter)network layer should never treat packets differently depend‐
       ing 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 pat‐
       tern  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	trans‐
       mit 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 man‐
       age  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	decre‐
       ment 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 (4.3 BSD  uses
       30, 4.2 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 tel‐
       net(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:

       · 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.

       · 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.

       · 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.

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 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 condi‐
	 tions.

SEE ALSO
       netstat(1), ifconfig(8).

HISTORY
       The ping command appeared in 4.3BSD.

       The version described here is its descendant specific to Linux.

SECURITY
       ping requires CAP_NET_RAWIO capability to be executed. It may  be  used
       as set-uid root.

AVAILABILITY
       ping  is part of iputils package and the latest versions are  available
       in   source    form    at    http://www.skbuff.net/iputils/iputils-cur‐
       rent.tar.bz2.

iputils-101006			 12 April 2011			       PING(8)
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