ping

PING(1)                      User's Reference Manual                     PING(1)

NAME
     ping — send ICMP ECHO_REQUEST packets to network hosts

SYNOPSIS
     ping [option ...] 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.

OPTIONS
     --address
             Send ICMP_ADDRESS packets (root only).

     --mask  Same as --address.

     --echo  Send ICMP_ECHO packets (default).

     --timestamp
             Send ICMP_TIMESTAMP packets.

     -t, --type type
             Send type packets.

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

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

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

     -n, --numeric
             Numeric output only.  No attempt will be made to lookup symbolic
             names for host addresses.

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

     -R, --route
             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, --ignore-routing
             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, --size 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
             Verbose output.  ICMP packets other than ECHO_RESPONSE that are
             received are listed.

     --ttl N
             Set N as the packet time-to-live.

     -T, --tos num
             Set num as the packet type of service (TOS).

     -w, --timeout N
             Stop after N seconds of sending packets.

     -W, --linger N
             Number of seconds to wait for response.

     --ip-timestamp flag
             IP timestamp of type flag, which is one of "tsonly" and "tsaddr".

     -?, --help
             Display a help list.

     --usage
             Display a short usage message.

     -V, --version
             Print the program version.

     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 Network Utilities           February 9, 2019           GNU Network Utilities