PING(8)                 NetBSD System Manager's Manual                 PING(8)

NAME
     ping -- send ICMP ECHO_REQUEST packets to network hosts

SYNOPSIS
     ping [-adDfLnoPqQrRv] [-c count] [-E policy] [-g gateway] [-h host]
          [-i interval] [-I srcaddr] [-l preload] [-p pattern] [-s packetsize]
          [-t tos] [-T ttl] [-w deadline] 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:

     -a      Emit an audible beep (by sending an ascii BEL character to the
             standard error output) after each non-duplicate response is
             received.  This is disabled for flood pings as it would probably
             cause temporary insanity.

     -c count
             Stop after sending (and waiting the specified delay to receive)
             count ECHO_RESPONSE packets.

     -d      Set the SO_DEBUG option on the socket being used.

     -D      Set the Don't Fragment bit in the IP header.  This can be used to
             determine the path MTU.

     -E policy
             Use IPsec policy specification string policy for packets.  For
             the format of specification string, please refer
             ipsec_set_policy(3).  Please note that this option is same as -P
             in KAME/FreeBSD and KAME/BSDI (as -P was already occupied in
             NetBSD).

     -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 net-
             work and should be used with caution.

     -g gateway
             Use Loose Source Routing to send the ECHO_REQUEST packets via
             gateway.

     -i interval
             Wait interval seconds between sending each packet.  The default
             is to wait for one second between each packet, except when the -f
             option is used the wait interval is 0.01 seconds.

     -I srcaddr
             Set the source IP address to srcaddr which can be a hostname or
             an IP number.  For multicast datagrams, it also specifies the
             outgoing interface.

     -h host
             is an alternate way of specifying the target host instead of as
             the last argument.

     -l preload
             If preload is specified, ping sends that many packets as fast as
             possible before falling into its normal mode of behavior.  Only
             the super-user may use this option.

     -L      Disable loopback when sending to multicast destinations, so the
             transmitting host doesn't see the ICMP requests.

     -n      Numeric output only.  No attempt will be made to look up symbolic
             names for host addresses.

     -o      Exit successfully after receiving one reply packet.

     -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.

     -P      Use a pseudo-random sequence for the data instead of the default,
             fixed sequence of incrementing 8-bit integers.  This is useful to
             foil compression on PPP and other links.

     -q      Quiet output.  Nothing is displayed except the summary lines at
             startup time and when finished.

     -Q      Do not display responses such as Network Unreachable ICMP mes-
             sages concerning the ECHO_REQUESTs sent.

     -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)).

     -R      Record Route.  Includes the RECORD_ROUTE option in the
             ECHO_REQUEST packet and displays the route buffer on returned
             packets.  This should show the path to the target host and back,
             which is especially useful in the case of asymmetric routing.
             Note that the IP header is only large enough for nine such
             addresses, and only seven when using the -g option.  This is why
             it was necessary to invent traceroute(8).  Many hosts ignore or
             discard this option.

     -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.  The maximum allowed value is
             65467 bytes.

     -T ttl  Use the specified time-to-live.

     -t tos  Use the specified hexadecimal type of service.

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

     -w deadline
             Specifies a timeout, in seconds, before ping exits regardless of
             how many packets have been sent or received.

     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 calcula-
     tion, although the round trip time of these packets is used in calculat-
     ing 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.
     The summary information can be displayed while ping is running by sending
     it a SIGINFO signal (see the ``status'' argument for stty(1) for more
     information).

     ping continually sends one datagram per second, and prints one line of
     output for every ECHO_RESPONSE returned.  On a trusted system with IP
     Security Options enabled, if the network idiom is not MONO, ping also
     prints a second line containing the hexadecimal representation of the IP
     security option in the ECHO_RESPONSE.  If the -c count option is given,
     only that number of requests is sent.  No output is produced if there is
     no response.  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 an interrupt (SIGINT), a brief summary is dis-
     played.  When not using the -f (flood) option, the first interrupt, usu-
     ally generated by control-C or DEL, causes ping to wait for its outstand-
     ing requests to return.  It will wait no longer than the longest round
     trip time encountered by previous, successful pings.  The second inter-
     rupt stops ping immediately.

     This program is intended for use in network testing, measurement and man-
     agement.  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 arbi-
     trary 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 to compute 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 retrans-
     missions.  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 (4.3BSD uses 30, 4.2BSD
     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:

     o   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.

     o   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.

     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.

EXIT STATUS
     ping returns 0 on success (the host is alive), and non-zero if the argu-
     ments are incorrect or the host is not responding.

SEE ALSO
     netstat(1), icmp(4), inet(4), ip(4), ifconfig(8), routed(8), spray(8),
     traceroute(8)

HISTORY
     The ping command appeared in 4.3BSD.  IPsec support was added by
     WIDE/KAME project.

BUGS
     Flood pinging is not recommended in general, and flood pinging a broad-
     cast or multicast address should only be done under very controlled con-
     ditions.

     The ping program has evolved differently under different operating sys-
     tems, and in some cases the same flag performs a different function under
     different operating systems.  The -t flag conflicts with FreeBSD.  The
     -a, -c, -i, -I, -l, -p, -P, -s, and -t flags conflict with Solaris.

     Some 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.

NetBSD 5.0_STABLE               March 21, 2006               NetBSD 5.0_STABLE
