PING(8)                                                System Manager's Manual: iputils                                                PING(8)

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.
 

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