Provided by: iputils-ping_20101006-1ubuntu1_amd64 bug

NAME

       ping, ping6 - send ICMP ECHO_REQUEST to network hosts

SYNOPSIS

       ping  [-LRUbdfnqrvVaAB]  [-c  count] [-m mark] [-i interval] [-l preload] [-p pattern] [-s
       packetsize] [-t ttl] [-w deadline] [-F flowlabel] [-I interface] [-M hint]  [-N  nioption]
       [-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.

       ping6 can also send Node Information Queries (RFC4620).

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.

       -m mark
              use mark to tag the packets going out. This is useful for variety of reasons within
              the kernel such as using policy routing to select specific outbound processing.

       -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 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 nioption
              Send ICMPv6 Node Information Queries (RFC4620), instead of Echo Request.

              name   Queries for Node Names.

              ipv6   Queries for IPv6 Addresses. There are several IPv6 specific flags.

                     ipv6-global
                            Request IPv6 global-scope addresses.

                     ipv6-sitelocal
                            Request IPv6 site-local addresses.

                     ipv6-linklocal
                            Request IPv6 link-local addresses.

                     ipv6-all
                            Request IPv6 addresses on other interfaces.

              ipv4   Queries for IPv4 Addresses.  There is one IPv4 specific flag.

                     ipv4-all
                            Request IPv4 addresses on other interfaces.

              subject-ipv6=ipv6addr
                     IPv6 subject address.

              subject-ipv4=ipv4addr
                     IPv4 subject address.

              subject-name=nodename
                     Subject name.  If it contains more than one dot, fully-qualified domain name
                     is assumed.

              subject-fqdn=nodename
                     Subject name.  Fully-qualified domain name is always assumed.

       -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.

       -D     Print timestamp (unix time + microseconds as in gettimeofday) before each line.

       -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 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 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  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.

       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.  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(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.