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ping


SYNOPSIS

       ping  [ -LRUbdfnqrvVaAB]  [ -c count]  [ -i interval]  [ -l preload]  [
       -p pattern]  [ -s packetsize]  [ -t ttl]  [ -w deadline]  [ -F  flowla-
       bel]  [ -I interface]  [ -M hint]  [ -Q tos]  [ -S sndbuf]  [ -T times-
       tamp 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.


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.

       -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
              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.

       -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
              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


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.



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   for   anonymous  ftp  ftp://ftp.inr.ac.ru/ip-rout-
       ing/iputils-current.tar.gz.

iputils-020927                 27 September 2002                       PING(8)

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