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ping - send ICMP ECHO_REQUEST packets to network hosts

 

NAME

      ping - send ICMP ECHO_REQUEST packets to network hosts
 

SYNOPSIS

      ping [-AaDdfnoQqRrv] [-c count] [-G sweepmaxsize] [-g sweepminsize]
           [-h sweepincrsize] [-i wait] [-l preload] [-M mask | time] [-m ttl]
           [-P policy] [-p pattern] [-S src_addr] [-s packetsize] [-t timeout]
           [-W waittime] [-z tos] host
      ping [-AaDdfLnoQqRrv] [-c count] [-I iface] [-i wait] [-l preload]
           [-M mask | time] [-m ttl] [-P policy] [-p pattern] [-S src_addr]
           [-s packetsize] [-T ttl] [-t timeout] [-W waittime] [-z tos]
           mcast-group
 

DESCRIPTION

      The ping utility 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.  If this option is specified in conjunction with ping
              sweeps, each sweep will consist of count packets.
 
      -D      Set the Don’t Fragment bit.
 
      -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.
 
      -G sweepmaxsize
              Specify the maximum size of ICMP payload when sending sweeping
              pings.  This option is required for ping sweeps.
 
      -g sweepminsize
              Specify the size of ICMP payload to start with when sending
              sweeping pings.  The default value is 0.
 
      -h sweepincrsize
              Specify the number of bytes to increment the size of ICMP payload
              after each sweep when sending sweeping pings.  The default value
              is 1.
 
      -I iface
              Source multicast packets with the given interface address.  This
              flag only applies if the ping destination is a multicast address.
 
      -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.
 
      -L      Suppress loopback of multicast packets.  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 mask | time
              Use ICMP_MASKREQ or ICMP_TSTAMP instead of ICMP_ECHO.  For mask,
              print the netmask of the remote machine.  Set the
              net.inet.icmp.maskrepl MIB variable to enable ICMP_MASKREPLY.
              For time, print the origination, reception and transmission
              timestamps.
 
      -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.
 
      -n      Numeric output only.  No attempt will be made to lookup symbolic
              names for host addresses.
 
      -o      Exit successfully after receiving one reply packet.
 
      -P policy
              policy specifies IPsec policy for the ping session.  For details
              please refer to ipsec(4) and ipsec_set_policy(3).
 
      -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      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 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.
 
      -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 specify val‐
              ues more than default.  This option cannot be used with ping
              sweeps.
 
      -T ttl  Set the IP Time To Live for multicasted packets.  This flag only
              applies if the ping destination is a multicast address.
 
      -t timeout
              Specify a timeout, in seconds, before ping exits regardless of
              how many packets have been received.
 
      -v      Verbose output.  ICMP packets other than ECHO_RESPONSE that are
              received are listed.
 
      -W waittime
              Time in milliseconds to wait for a reply for each packet sent.
              If a reply arrives later, the packet is not printed as replied,
              but considered as replied when calculating statistics.
 
      -z tos  Use the specified type of service.
 
      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.
      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.
      The ping utility 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).
      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.
      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 recommends setting the TTL field for IP packets
      to 64, 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:
 
            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.
 
            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.
 
            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.
      The ping utility 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 if
      an error occurred.
      netstat(1), ifconfig(8), routed(8), traceroute(8)
 

HISTORY

      The ping utility appeared in 4.3BSD.
 

AUTHORS

      The original ping utility 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.
 

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