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32 .\" @(#)ping.8 8.2 (Berkeley) 12/11/93
33 .\" $FreeBSD: src/sbin/ping/ping.8,v 1.25.2.11 2003/02/23 21:03:24 trhodes Exp $
35 .Dd September 25, 2001
42 packets to network hosts
52 .Op Fl s Ar packetsize
66 .No protocol Ap s mandatory
69 .Tn ICMP ECHO_RESPONSE
70 from a host or gateway.
78 and then an arbitrary number of
80 bytes used to fill out the packet.
81 The options are as follows:
82 .Bl -tag -width indent
88 character when no packet is received before the next packet
90 To cater for round-trip times that are longer than the interval
91 between transmissions, further missing packets cause a bell only
92 if the maximum number of unreceived packets has increased.
98 character in the output when any packet is received.
99 This option is ignored
100 if other format options are present.
107 If this option is not specified,
109 will operate until interrupted.
113 option on the socket being used.
116 Outputs packets as fast as they come back or one hundred times per second,
122 is printed, while for every
124 received a backspace is printed.
125 This provides a rapid display of how many packets are being dropped.
126 Only the super-user may use this option.
128 This can be very hard on a network and should be used with caution.
134 .Em between sending each packet .
135 The default is to wait for one second between each packet.
136 The wait time may be fractional, but only the super-user may specify
137 values less than 1 second.
138 This option is incompatible with the
141 .It Fl I Ar interface
142 Source multicast packets with the given interface address.
143 This flag only applies if the ping destination is a multicast address.
149 sends that many packets as fast as possible before falling into its normal
151 Only the super-user may use this option.
153 Set the IP Time To Live for outgoing packets.
154 If not specified, the kernel uses the value of the
158 Suppress loopback of multicast packets.
159 This flag only applies if the ping destination is a multicast address.
162 No attempt will be made to lookup symbolic names for host addresses.
164 You may specify up to 16
166 bytes to fill out the packet you send.
167 This is useful for diagnosing data-dependent problems in a network.
170 will cause the sent packet to be filled with all
174 specifies IPsec policy for the ping session.
175 For details please refer to
178 .Xr ipsec_set_policy 3 .
180 Somewhat quiet output.
182 display ICMP error messages that are in response to our query messages.
185 flag was required to display such errors, but
187 displays all ICMP error messages.
188 On a busy machine, this output can
194 prints out any ICMP error messages caused by its own ECHO_REQUEST
198 Nothing is displayed except the summary lines at startup time and
207 the route buffer on returned packets.
208 Note that the IP header is only large enough for nine such routes;
211 command is usually better at determining the route packets take to a
212 particular destination.
213 If more routes come back than should, such as due to an illegal spoofed
214 packet, ping will print the route list and then truncate it at the correct
216 Many hosts ignore or discard the
220 Bypass the normal routing tables and send directly to a host on an attached
222 If the host is not on a directly-attached network, an error is returned.
223 This option can be used to ping a local host through an interface
224 that has no route through it
225 (e.g., after the interface was dropped by
227 .It Fl s Ar packetsize
228 Specify the number of data bytes to be sent.
229 The default is 56, which translates into 64
231 data bytes when combined
235 Only the super-user may use this option.
237 Use the following IP address as the source address in outgoing packets.
238 On hosts with more than one IP address, this option can be used to
239 force the source address to be something other than the IP address
240 of the interface the probe packet is sent on.
241 If the IP address is not one of this machine's interface addresses,
242 an error is returned and nothing is sent.
244 Specify a timeout, in seconds, before ping exits regardless of how
245 many packets have been received.
247 Set the IP Time To Live for multicasted packets.
248 This flag only applies if the ping destination is a multicast address.
254 that are received are listed.
259 for fault isolation, it should first be run on the local host, to verify
260 that the local network interface is up and running.
261 Then, hosts and gateways further and further away should be
263 Round-trip times and packet loss statistics are computed.
264 If duplicate packets are received, they are not included in the packet
265 loss calculation, although the round trip time of these packets is used
266 in calculating the round-trip time statistics.
267 When the specified number of packets have been sent
269 or if the program is terminated with a
271 a brief summary is displayed, showing the number of packets sent and
272 received, and the minimum, mean, maximum, and standard deviation of
273 the round-trip times.
283 signal, the current number of packets sent and received, and the
284 minimum, mean, and maximum of the round-trip times will be written to
285 the standard error output.
287 This program is intended for use in network testing, measurement and
289 Because of the load it can impose on the network, it is unwise to use
291 during normal operations or from automated scripts.
292 .Sh ICMP PACKET DETAILS
293 An IP header without options is 20 bytes.
297 packet contains an additional 8 bytes worth of
299 header followed by an arbitrary amount of data.
302 is given, this indicated the size of this extra piece of data
304 Thus the amount of data received inside of an IP packet of type
307 will always be 8 bytes more than the requested data space
312 If the data space is at least eight bytes large,
314 uses the first eight bytes of this space to include a timestamp which
315 it uses in the computation of round trip times.
316 If less than eight bytes of pad are specified, no round trip times are
318 .Sh DUPLICATE AND DAMAGED PACKETS
320 will report duplicate and damaged packets.
321 Duplicate packets should never occur when pinging a unicast address,
322 and seem to be caused by
323 inappropriate link-level retransmissions.
324 Duplicates may occur in many situations and are rarely
326 a good sign, although the presence of low levels of duplicates may not
327 always be cause for alarm.
328 Duplicates are expected when pinging a broadcast or multicast address,
329 since they are not really duplicates but replies from different hosts
332 Damaged packets are obviously serious cause for alarm and often
333 indicate broken hardware somewhere in the
335 packet's path (in the network or in the hosts).
336 .Sh TRYING DIFFERENT DATA PATTERNS
339 layer should never treat packets differently depending on the data
340 contained in the data portion.
341 Unfortunately, data-dependent problems have been known to sneak into
342 networks and remain undetected for long periods of time.
343 In many cases the particular pattern that will have problems is something
344 that does not have sufficient
346 such as all ones or all zeros, or a pattern right at the edge, such as
349 necessarily enough to specify a data pattern of all zeros (for example)
350 on the command line because the pattern that is of interest is
351 at the data link level, and the relationship between what you type and
352 what the controllers transmit can be complicated.
354 This means that if you have a data-dependent problem you will probably
355 have to do a lot of testing to find it.
356 If you are lucky, you may manage to find a file that either
358 be sent across your network or that takes much longer to transfer than
359 other similar length files.
360 You can then examine this file for repeated patterns that you can test
368 value of an IP packet represents the maximum number of IP routers
369 that the packet can go through before being thrown away.
370 In current practice you can expect each router in the Internet to decrement
373 field by exactly one.
377 specification states that the
381 packets should be set to 60, but many systems use smaller values
387 The maximum possible value of this field is 255, and most
393 .Tn ICMP ECHO_REQUEST
395 This is why you will find you can
397 some hosts, but not reach them with
404 prints the ttl value from the packet it receives.
405 When a remote system receives a ping packet, it can do one of three things
408 field in its response:
411 Not change it; this is what
413 systems did before the
418 value in the received packet will be 255 minus the
419 number of routers in the round-trip path.
421 Set it to 255; this is what current
426 value in the received packet will be 255 minus the
427 number of routers in the path
435 Set it to some other value.
436 Some machines use the same value for
438 packets that they use for
440 packets, for example either 30 or 60.
441 Others may use completely wild values.
446 command returns an exit status of zero if at least one response was
447 heard from the specified
449 a status of two if the transmission was successful but no responses
450 were received; or another value
453 if an error occurred.
467 command was written by
469 while at the US Army Ballistics
472 Many Hosts and Gateways ignore the
476 The maximum IP header length is too small for options like
478 to be completely useful.
480 not much that can be done about this, however.
482 Flood pinging is not recommended in general, and flood pinging the
483 broadcast address should only be done under very controlled conditions.
487 option is not worth much on busy hosts.
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