ping(8) 						      System Manager's Manual							   ping(8)

NAME

       ping - Sends ICMP ECHO_REQUEST packets to network hosts

SYNOPSIS

       /usr/sbin/ping  [-dfnqruvLR]  [-b  num]	[-c  count]  [-i  wait]  [-l  preload]	[-p  pattern]  [-s  packetsize] [-t number] [-I interface]
       [-G[!]@addr1@addr2...] [-V version] host

FLAGS

       Specifies the size of the receive buffer.  You can use this when specifying very large packet sizes with the -s flag.  By default, the size
       of  the	receive  buffer  is set to 48K or to the size specified by the -s flag, whichever is greater.  The -b  flag overrides the default.
       Stops after sending (and receiving) count ECHO_RESPONSE packets.  Set the SO_DEBUG option on the socket being used.  Floods ping.   Outputs
       packets as fast as they come back or 100 times per second, whichever is more.  For every ECHO_REQUEST sent, a . (dot) is printed, while for
       every ECHO_REPLY received a backspace is used.  This provides a rapid display of how many packets are being dropped.   Only  the  superuser
       may  use  this  option.	This can be very hard on a network and should be used with caution (see Cautions).  Specifies the source route for
       packets to travel to the destination host.  The route consists of one or more node names or addresses.  Use the ampersand character (@)	to
       separate multiple addresses.  You can specify up to 10 addresses.

	      The exclamation mark (!) indicates that this is a strict source route; ping uses only the specified hosts for intermediate hops.

	      If  any  of the specified addresses is a hostname, a lookup is performed and the protocol common to all addresses is used.  If there
	      is no common protocol (for example, one host has only IPv4 address and one host has only IPv6 address), an error is printed.  If all
	      hosts have both IPv4 and IPv6 addresses, IPv6 is used.  You can override this option with the -V option.	Waits wait seconds between
	      sending each packet.  The default is to wait for 1 second between each packet.  This option is  incompatible  with  the  -f  option.
	      Sends  packets  through interface instead of using the interface specified in the routing tables for the host.  Displays every 100th
	      reply only and displays a message indicating lost packets.

	      A packet loss rate of just 1% is enough to seriously impact UDP-based protocols like NFS.  This option enables you to  measure  loss
	      rates and to determine how bursty they are.  All lost messages are reported with the following message: Lost sequence number(s) num-
	      ber The number value is a single number or a range or numbers.  If preload is specified, ping sends that many  packets  as  fast	as
	      possible	before	falling into its normal mode of behavior. Only the superuser may use this option.  This can be very hard on a net-
	      work and should be used with caution (see Cautions).  Numeric output only.  No attempt will be made to look up  symbolic	names  for
	      host  addresses. This occurs only when displaying ICMP packets other than ECHO_RESPONSE.	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 1s (ones).	Quiets output.	Nothing is displayed except the summary lines at start-up time and
	      when finished.  [ICMP over IPv4 only]  Records 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.  Bypasses the normal routing tables and directly sends 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  send  ping	to  a  local  host
	      through an interface that has no route through it (for example, after the interface was dropped by routed).  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.  Sets the timeout period (in seconds) for ping to wait before terminating.	The default timeout period is  10  seconds.   This
	      option  is  only	useful	with  -c  1  option.   Displays  the time in microseconds (three decimal places).  In order to ensure this
	      microsecond precision, the NTP_TIME and MICRO_TIME kernel options must be on.  By default NTP_TIME and MICRO_TIME kernel options are
	      off.   If  these	kernel	options are off and this flag is used, the time is displayed to three decimal places, but in milliseconds.
	      Specifies verbose output.  ICMP packets other than ECHO_RESPONSE that are received are listed.  Specifies the Internet Protocol (IP)
	      version  number  to  enable  the	resolver  to return the correct address.  If you are issuing a ping command to a host name (not IP
	      address) that has both IPv4 and IPv6 addresses, by default the command is issued using the IPv6 address.	Use the -V4 option if  you
	      want to use the IPv4 address.

DESCRIPTION

       The  ping  command  uses  the  ICMP  (Internet  Control	Message  Protocol)  protocol's	mandatory  ECHO_REQUEST datagram to elicit an ICMP
       ECHO_RESPONSE from the specified host or gateway host, where host is a network name or IP address.  ECHO_REQUEST datagrams (pings) have	an
       IP (Internet Protocol) and ICMP header, followed by a struct timeval and then an arbitrary number of pad bytes used to fill out the packet.
       The operating system supports both ICMPv4 and ICMPv6.

       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 sent the ping command.  Round-trip times and packet loss statistics are com-
       puted.  If duplicate packets are received, they are not included in the packet loss calculations, although the  round-trip  time  of  these
       packets	is  used in calculating the minimum, average, and 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.

       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.

   ICMPv4 Packet Details
       An  IPv4  header without options is 20 bytes.  An ICMPv4 ECHO_REQUEST packet contains an additional 8 bytes worth of ICMPv4 header followed
       by an arbitrary amount of data.	When a packetsize is given, this indicates the size of this extra piece  of  data  (the  default  is  56).
       Thus,  the  amount  of  data  received inside of an IPv4 packet of type ICMP ECHO_REPLY will always be 8 bytes more than the requested data
       space (the ICMPv4 header).

       If the data space is at least 8 bytes large, ping uses the first 8 bytes of this space to include a timestamp, which it uses in the  compu-
       tation of round-trip times.  If less than 8 bytes of pad are specified, no round-trip times are given.

   Duplicate and Damaged Packets
       The  ping  command 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 net-
       work 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 does not have sufficient transitions, such as all 1s (ones) or all 0s (zeros), or a  pat-
       tern right at the edge, such as almost all 0s (zeros).  It is not necessarily enough to specify a data pattern of all 0s (zeros) (for exam-
       ple) on the command line because the pattern that is of interest is at the data-link level, and the relationship between what you enter 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.

   IPv4 TTL Details
       The  TTL value of an IPv4 packet represents the maximum number of IPv4 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 1 (one).

       The TCP/IP specification states that the TTL field for TCP packets should be set to 60, but many systems use smaller  values  (4.3BSD  uses
       30, 4.2BSD used 15).

       The  maximum  possible  value of this field is 255, and most UNIX compatible systems set the TTL field of ICMP ECHO_REQUEST packets to 255.
       This is why you will find you can use the ping command on some hosts, but not reach them with telnet or ftp.

       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 compatible systems did before the 4.3BSD
       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 compatible 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 host that received the ping	command.   Set	it  to	some  other  value.   Some
       machines use the same value for ICMPv4 packets that they use for TCP packets; for example, either 30 or 60.  Others may use completely wild
       values.

CAUTIONS

       Many hosts and gateways ignore the RECORD_ROUTE option.

       Flooding and preloading the ping command is not recommended in general, and flooding ping on the broadcast  address  should  only  be  done
       under very controlled conditions.

FILES

       Specifies the command path

RELATED INFORMATION

       Commands: netstat(1), ifconfig(8)

       Daemons: gated(8), routed(8)

       RFC 792, Internet Control Message Protocol, Postel, J.

       RFC  2463,  Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification, Conta, A., and Deering, S.
       delim off

																	   ping(8)