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32 .\" @(#)ping.8 8.2 (Berkeley) 12/11/93
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. The options are as follows:
81 .Bl -tag -width indent
87 character when no packet is received before the next packet
89 To cater for round-trip times that are longer than the interval
90 between transmissions, further missing packets cause a bell only
91 if the maximum number of unreceived packets has increased.
97 character in the output when any packet is received.
98 This option is ignored
99 if other format options are present.
106 If this option is not specified,
108 will operate until interrupted.
112 option on the socket being used.
115 Outputs packets as fast as they come back or one hundred times per second,
121 is printed, while for every
123 received a backspace is printed.
124 This provides a rapid display of how many packets are being dropped.
125 Only the super-user may use this option.
127 This can be very hard on a network and should be used with caution.
133 .Em between sending each packet .
134 The default is to wait for one second between each packet.
135 The wait time may be fractional, but only the super-user may specify
136 values less then 1 second.
137 This option is incompatible with the
140 .It Fl I Ar interface
141 Source multicast packets with the given interface address.
142 This flag only applies if the ping destination is a multicast address.
148 sends that many packets as fast as possible before falling into its normal
150 Only the super-user may use this option.
152 Set the IP Time To Live for outgoing packets.
153 If not specified, the kernel uses the value of the
157 Suppress loopback of multicast packets.
158 This flag only applies if the ping destination is a multicast address.
161 No attempt will be made to lookup symbolic names for host addresses.
163 You may specify up to 16
165 bytes to fill out the packet you send.
166 This is useful for diagnosing data-dependent problems in a network.
169 will cause the sent packet to be filled with all
173 specifies IPsec policy for the ping session.
174 For details please refer to
177 .Xr ipsec_set_policy 3 .
179 Somewhat quiet output.
181 display ICMP error messages that are in response to our query messages.
184 flag was required to display such errors, but
186 displays all ICMP error messages. On a busy machine, this output can
187 be overbearing. Without the
191 prints out any ICMP error messages caused by its own ECHO_REQUEST
195 Nothing is displayed except the summary lines at startup time and
204 the route buffer on returned packets.
205 Note that the IP header is only large enough for nine such routes;
208 command is usually better at determining the route packets take to a
209 particular destination.
210 If more routes come back than should, such as due to an illegal spoofed
211 packet, ping will print the route list and then truncate it at the correct
213 Many hosts ignore or discard the
217 Bypass the normal routing tables and send directly to a host on an attached
219 If the host is not on a directly-attached network, an error is returned.
220 This option can be used to ping a local host through an interface
221 that has no route through it
222 (e.g., after the interface was dropped by
224 .It Fl s Ar packetsize
225 Specify the number of data bytes to be sent.
226 The default is 56, which translates into 64
228 data bytes when combined
232 Only the super-user may use this option.
234 Use the following IP address as the source address in outgoing packets.
235 On hosts with more than one IP address, this option can be used to
236 force the source address to be something other than the IP address
237 of the interface the probe packet is sent on. If the IP address
238 is not one of this machine's interface addresses, an error is
239 returned and nothing is sent.
241 Specify a timeout, in seconds, before ping exits regardless of how
242 many packets have been recieved.
244 Set the IP Time To Live for multicasted packets.
245 This flag only applies if the ping destination is a multicast address.
251 that are received are listed.
256 for fault isolation, it should first be run on the local host, to verify
257 that the local network interface is up and running.
258 Then, hosts and gateways further and further away should be
260 Round-trip times and packet loss statistics are computed.
261 If duplicate packets are received, they are not included in the packet
262 loss calculation, although the round trip time of these packets is used
263 in calculating the round-trip time statistics.
264 When the specified number of packets have been sent
266 or if the program is terminated with a
268 a brief summary is displayed, showing the number of packets sent and
269 received, and the minimum, maximum, mean, and standard deviation of
270 the round-trip times.
272 This program is intended for use in network testing, measurement and
274 Because of the load it can impose on the network, it is unwise to use
276 during normal operations or from automated scripts.
277 .Sh ICMP PACKET DETAILS
278 An IP header without options is 20 bytes.
282 packet contains an additional 8 bytes worth of
284 header followed by an arbitrary amount of data.
287 is given, this indicated the size of this extra piece of data
289 Thus the amount of data received inside of an IP packet of type
292 will always be 8 bytes more than the requested data space
297 If the data space is at least eight bytes large,
299 uses the first eight bytes of this space to include a timestamp which
300 it uses in the computation of round trip times.
301 If less than eight bytes of pad are specified, no round trip times are
303 .Sh DUPLICATE AND DAMAGED PACKETS
305 will report duplicate and damaged packets.
306 Duplicate packets should never occur when pinging a unicast address,
307 and seem to be caused by
308 inappropriate link-level retransmissions.
309 Duplicates may occur in many situations and are rarely
311 a good sign, although the presence of low levels of duplicates may not
312 always be cause for alarm.
313 Duplicates are expected when pinging a broadcast or multicast address,
314 since they are not really duplicates but replies from different hosts
317 Damaged packets are obviously serious cause for alarm and often
318 indicate broken hardware somewhere in the
320 packet's path (in the network or in the hosts).
321 .Sh TRYING DIFFERENT DATA PATTERNS
324 layer should never treat packets differently depending on the data
325 contained in the data portion.
326 Unfortunately, data-dependent problems have been known to sneak into
327 networks and remain undetected for long periods of time.
328 In many cases the particular pattern that will have problems is something
329 that does not have sufficient
331 such as all ones or all zeros, or a pattern right at the edge, such as
334 necessarily enough to specify a data pattern of all zeros (for example)
335 on the command line because the pattern that is of interest is
336 at the data link level, and the relationship between what you type and
337 what the controllers transmit can be complicated.
339 This means that if you have a data-dependent problem you will probably
340 have to do a lot of testing to find it.
341 If you are lucky, you may manage to find a file that either
343 be sent across your network or that takes much longer to transfer than
344 other similar length files.
345 You can then examine this file for repeated patterns that you can test
353 value of an IP packet represents the maximum number of IP routers
354 that the packet can go through before being thrown away.
355 In current practice you can expect each router in the Internet to decrement
358 field by exactly one.
362 specification states that the
366 packets should be set to 60, but many systems use smaller values
372 The maximum possible value of this field is 255, and most
378 .Tn ICMP ECHO_REQUEST
380 This is why you will find you can
382 some hosts, but not reach them with
389 prints the ttl value from the packet it receives.
390 When a remote system receives a ping packet, it can do one of three things
393 field in its response:
396 Not change it; this is what
398 systems did before the
403 value in the received packet will be 255 minus the
404 number of routers in the round-trip path.
406 Set it to 255; this is what current
411 value in the received packet will be 255 minus the
412 number of routers in the path
420 Set it to some other value.
421 Some machines use the same value for
423 packets that they use for
425 packets, for example either 30 or 60.
426 Others may use completely wild values.
431 command returns an exit status of zero if at least one response was
432 heard from the specified
434 a status of two if the transmission was successful but no responses
435 were received; or another value
438 if an error occurred.
452 command was written by
454 while at the US Army Ballistics
457 Many Hosts and Gateways ignore the
461 The maximum IP header length is too small for options like
463 to be completely useful.
465 not much that can be done about this, however.
467 Flood pinging is not recommended in general, and flood pinging the
468 broadcast address should only be done under very controlled conditions.
472 option is not worth much on busy hosts.
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