Provided by: inetutils-ping_1.9.4-3ubuntu0.1_amd64 bug

NAME

       ping — send ICMP ECHO_REQUEST packets to network hosts

SYNOPSIS

       ping [-Rdfnqrv] [-c count] [-i wait] [-l preload] [-p pattern] [-s packetsize] host

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.  The options  are  as
       follows:

       -c count
               Stop after sending (and receiving) count ECHO_RESPONSE packets.

       -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 network and should
               be used with caution.

       -i wait
               Wait  wait  seconds  between  sending each packet.  The default is to wait for one second between
               each packet.  This option is incompatible with the -f option.

       -l preload
               If preload is specified, ping sends that many packets as fast as possible before falling into its
               normal mode of behavior.

       -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      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 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 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.

       -v      Verbose output.  ICMP packets other than ECHO_RESPONSE that are received are listed.

       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 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.

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 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.

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.   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).

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 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 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 completely 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(1), routed(8)

HISTORY

       The ping command appeared in 4.3BSD.

GNU inetutils                                    April 28, 1995                                          PING(1)