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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]  [ -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


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 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 dis-
              play 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 required.

       -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
              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 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 capability) 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 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  (prohibit  frag-
              mentation,  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 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 ter-
       minated 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 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.  Dupli-
       cates 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).

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
       doesn't have sufficient ''transitions'', such as all ones or all zeros, or  a  pat-
       tern  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
       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 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  com-
         pletely 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 conditions.

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-current.tar.bz2.



iputils-071127                   22 March 2017                         PING(8)

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