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RedHat 9 (Linux i386) - man page for ping (redhat section 8)

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

       ping, ping6 - send ICMP ECHO_REQUEST to network hosts

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

       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.

       -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.

       -c count
	      Stop after sending count ECHO_REQUEST packets. With deadline option, ping waits for
	      count ECHO_REPLY packets, until the timeout 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  hundred  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 values 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

       -l preload
	      If  preload is specified, ping sends that many packets not waiting 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  desti-
	      nation is a multicast address.

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

       -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 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 redefined as congestion control), 1-4 for Type of Service
	      and  5-7	for Precedence.  Possible settings for Type of Service are: minimal cost:
	      0x02, reliability: 0x04, throughput: 0x08, low  delay:  0x10.   Multiple	TOS  bits
	      should  not  be set simultaneously.  Possible settings for special Precedence range
	      from priority (0x20) to net control (0xe0).  You must be root (CAP_NET_ADMIN  capa-
	      bility)  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 Differentiated Services (DS), consisting of: bits 0-1 of
	      separate data (ECN will be used, here), and bits	2-7  of  Differentiated  Services
	      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 dis-
	      plays  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  inter-
	      face.   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

       -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 (prohibit 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 running. Then, hosts and gateways further and
       further away should be ``pinged''. Round-trip times and packet loss  statistics	are  com-
       puted.  If duplicate packets are received, they are not included in the packet loss calcu-
       lation, although the round trip time of these packets is used  in  calculating  the  mini-
       mum/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
       displayed.  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 opera-
       tions or from automated scripts.

       An IP header without options is 20 bytes.  An ICMP ECHO_REQUEST packet contains	an  addi-
       tional 8 bytes worth of ICMP header followed by an arbitrary amount of data.  When a pack-
       etsize 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.

       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 con-
       tained  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

       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.

       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 (4.3 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 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

       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  val-

       o Many Hosts and Gateways ignore the RECORD_ROUTE option.

       o 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.

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

       netstat(1), ifconfig(8).

       The ping command appeared in 4.3BSD.

       The version described here is its descendant specific to Linux.

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

       ping  is part of iputils package and the latest versions are  available in source form for
       anonymous ftp ftp://ftp.inr.ac.ru/ip-routing/iputils-current.tar.gz.

iputils-020927				27 September 2002				  PING(8)

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