Ping

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ping .. pong

ping [from the submariners' term for a sonar pulse]

1. n. Slang term for a small network message (ICMP ECHO) sent by a computer to check for the presence and alertness of another. The Unix command ping(8) can be used to do this manually (note that ping(8)'s author denies the widespread folk etymology that the name was ever intended as acronym for `Packet INternet Groper'). Occasionally used as a phone greeting. See ACK, also ENQ.

2. vt. To verify the presence of.

3. vt. To get the attention of.

4. vt. To send a message to all members of a mailing list requesting an ACK (in order to verify that everybody's addresses are reachable). "We haven't heard much of anything from Geoff, but he did respond with an ACK both times I pinged jargon-friends."

5. n. A quantum packet of happiness. People who are very happy tend to exude pings; furthermore, one can intentionally create pings and aim them at a needy party (e.g., a depressed person). This sense of ping may appear as an exclamation; "Ping!" (I'm happy; I am emitting a quantum of happiness; I have been struck by a quantum of happiness). The form "pingfulness", which is used to describe people who exude pings, also occurs. (In the standard abuse of language, "pingfulness" can also be used as an exclamation, in which case it's a much stronger exclamation than just "ping"!). Oppose blargh.


PingStorm


man ping

SYNOPSIS

      ping  [ -LRUbdfnqrvVaA]  [ -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]  [ hop  ...]
      destination



DESCRIPTION

      ping uses the ICMP protocol's mandatory ECHO_REQUEST data-
      gram to elicit an ICMP ECHO_RESPONSE from a host or  gate-
      way.   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.
      -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  display  of  how  many  packets  are   being
             dropped.   If interval is not given, it sets inter-
             val 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.
             If preload is specified, ping sends that many pack-
             ets 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 data-
             grams.  tos can be either decimal  or  hex  number.
             Traditionally  (RFC1349),  these  have  been inter-
             preted as: 0 for reserved  (currently  being  rede-
             fined  as congestion control), 1-4 for Type of Ser-
             vice and 5-7 for Precedence.  Possible settings for
             Type  of Service are: minimal cost: 0x02, reliabil-
             ity: 0x04, throughput: 0x08, low delay: 0x10.  Mul-
             tiple  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  ker-
             nel.   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 sum-
             mary 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
      -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 fragmentation, 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 fail-
             ures.
      -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.
      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 fur-
      ther and further away  should  be  ``pinged.  Round-trip
      times  and packet loss statistics are computed.  If dupli-
      cate 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/aver-
      age/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. 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.
      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 inap-
      propriate   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  dif-
      ferently  depending on the data contained in the data por-
      tion.  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 pat-
      tern  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  num-
      ber  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
        value in the received packet will be 255 minus the  num-
        ber of routers in the round-trip path.
      o Set  it  to 255; this is what current Berkeley Unix sys-
        tems 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.
      o 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

      o Many  Hosts and Gateways ignore the RECORD_ROUTE option.
      o 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.
      o 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  for  anonymous  ftp
      ftp://ftp.inr.ac.ru/ip-routing/iputils-current.tar.gz.


External Links

The Story of the PING Program

Source code of PING: