1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
|
.\" Copyright (c) 1985, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)ping.8 8.2 (Berkeley) 12/11/93
.\" $FreeBSD$
.\"
.Dd October 2, 2002
.Dt PING 8
.Os
.Sh NAME
.Nm ping
.Nd send
.Tn ICMP ECHO_REQUEST
packets to network hosts
.Sh SYNOPSIS
.Nm
.Op Fl AaDdfMnoQqRrv
.Op Fl c Ar count
.Op Fl i Ar wait
.Op Fl l Ar preload
.Op Fl m Ar ttl
.Op Fl P Ar policy
.Op Fl p Ar pattern
.Op Fl S Ar src_addr
.Op Fl s Ar packetsize
.Op Fl t Ar timeout
.Op Fl z Ar tos
.Ar host |
.Op Fl L
.Op Fl I Ar interface
.Op Fl T Ar ttl
.Ar mcast-group
.Sh DESCRIPTION
The
.Nm
utility uses the
.Tn ICMP
.No protocol Ap s mandatory
.Tn ECHO_REQUEST
datagram to elicit an
.Tn ICMP ECHO_RESPONSE
from a host or gateway.
.Tn ECHO_REQUEST
datagrams
.Pq Dq pings
have an IP and
.Tn ICMP
header, followed by a
.Dq struct timeval
and then an arbitrary number of
.Dq pad
bytes used to fill out the packet.
The options are as follows:
.Bl -tag -width indent
.It Fl A
Audible.
Output a bell
.Tn ( ASCII
0x07)
character when no packet is received before the next packet
is transmitted.
To cater for round-trip times that are longer than the interval
between transmissions, further missing packets cause a bell only
if the maximum number of unreceived packets has increased.
.It Fl a
Audible.
Include a bell
.Tn ( ASCII
0x07)
character in the output when any packet is received.
This option is ignored
if other format options are present.
.It Fl c Ar count
Stop after sending
(and receiving)
.Ar count
.Tn ECHO_RESPONSE
packets.
If this option is not specified,
.Nm
will operate until interrupted.
.It Fl D
Set the Don't Fragment bit.
.It Fl d
Set the
.Dv SO_DEBUG
option on the socket being used.
.It Fl f
Flood ping.
Outputs packets as fast as they come back or one hundred times per second,
whichever is more.
For every
.Tn ECHO_REQUEST
sent a period
.Dq .\&
is printed, while for every
.Tn 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.
.Bf -emphasis
This can be very hard on a network and should be used with caution.
.Ef
.It Fl I Ar interface
Source multicast packets with the given interface address.
This flag only applies if the ping destination is a multicast address.
.It Fl i Ar wait
Wait
.Ar wait
seconds
.Em between sending each packet .
The default is to wait for one second between each packet.
The wait time may be fractional, but only the super-user may specify
values less than 1 second.
This option is incompatible with the
.Fl f
option.
.It Fl L
Suppress loopback of multicast packets.
This flag only applies if the ping destination is a multicast address.
.It Fl l Ar preload
If
.Ar preload
is specified,
.Nm
sends that many packets as fast as possible before falling into its normal
mode of behavior.
Only the super-user may use this option.
.It Fl M
Use
.Dv ICMP_MASKREQ
instead of
.Dv ICMP_ECHO .
Print the netmask of the remote machine.
Set the
.Va net.inet.icmp.maskrepl
MIB variable to enable
.Dv ICMP_MASKREPLY .
.It Fl m Ar ttl
Set the IP Time To Live for outgoing packets.
If not specified, the kernel uses the value of the
.Va net.inet.ip.ttl
MIB variable.
.It Fl n
Numeric output only.
No attempt will be made to lookup symbolic names for host addresses.
.It Fl o
Exit successfully after receiving one reply packet.
.It Fl P Ar policy
.Ar policy
specifies IPsec policy for the ping session.
For details please refer to
.Xr ipsec 4
and
.Xr ipsec_set_policy 3 .
.It Fl p Ar pattern
You may specify up to 16
.Dq pad
bytes to fill out the packet you send.
This is useful for diagnosing data-dependent problems in a network.
For example,
.Dq Li \-p ff
will cause the sent packet to be filled with all
ones.
.It Fl Q
Somewhat quiet output.
.No Don Ap t
display ICMP error messages that are in response to our query messages.
Originally, the
.Fl v
flag was required to display such errors, but
.Fl v
displays all ICMP error messages.
On a busy machine, this output can be overbearing.
Without the
.Fl Q
flag,
.Nm
prints out any ICMP error messages caused by its own ECHO_REQUEST
messages.
.It Fl q
Quiet output.
Nothing is displayed except the summary lines at startup time and
when finished.
.It Fl R
Record route.
Includes the
.Tn RECORD_ROUTE
option in the
.Tn ECHO_REQUEST
packet and displays
the route buffer on returned packets.
Note that the IP header is only large enough for nine such routes;
the
.Xr traceroute 8
command is usually better at determining the route packets take to a
particular destination.
If more routes come back than should, such as due to an illegal spoofed
packet, ping will print the route list and then truncate it at the correct
spot.
Many hosts ignore or discard the
.Tn RECORD_ROUTE
option.
.It Fl 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
.Xr routed 8 ) .
.It Fl S Ar src_addr
Use the following IP address as the source address in outgoing packets.
On hosts with more than one IP address, this option can be used to
force the source address to be something other than the IP address
of the interface the probe packet is sent on.
If the IP address
is not one of this machine's interface addresses, an error is
returned and nothing is sent.
.It Fl s Ar packetsize
Specify the number of data bytes to be sent.
The default is 56, which translates into 64
.Tn ICMP
data bytes when combined
with the 8 bytes of
.Tn ICMP
header data.
Only the super-user may specify values more than default.
.It Fl T Ar ttl
Set the IP Time To Live for multicasted packets.
This flag only applies if the ping destination is a multicast address.
.It Fl t Ar timeout
Specify a timeout, in seconds, before ping exits regardless of how
many packets have been received.
.It Fl v
Verbose output.
.Tn ICMP
packets other than
.Tn ECHO_RESPONSE
that are received are listed.
.It Fl z Ar tos
Use the specified type of service.
.El
.Pp
When using
.Nm
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
.Dq 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 round-trip time statistics.
When the specified number of packets have been sent
(and received)
or if the program is terminated with a
.Dv SIGINT ,
a brief summary is displayed, showing the number of packets sent and
received, and the minimum, mean, maximum, and standard deviation of
the round-trip times.
.Pp
If
.Nm
receives a
.Dv SIGINFO
(see the
.Cm status
argument for
.Xr stty 1 )
signal, the current number of packets sent and received, and the
minimum, mean, and maximum of the round-trip times will be written to
the standard error output.
.Pp
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
.Nm
during normal operations or from automated scripts.
.Sh ICMP PACKET DETAILS
An IP header without options is 20 bytes.
An
.Tn ICMP
.Tn ECHO_REQUEST
packet contains an additional 8 bytes worth of
.Tn ICMP
header followed by an arbitrary amount of data.
When a
.Ar 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
.Tn ICMP
.Tn ECHO_REPLY
will always be 8 bytes more than the requested data space
(the
.Tn ICMP
header).
.Pp
If the data space is at least eight bytes large,
.Nm
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.
.Sh DUPLICATE AND DAMAGED PACKETS
The
.Nm
utility will report duplicate and damaged packets.
Duplicate packets should never occur when pinging a unicast address,
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.
Duplicates are expected when pinging a broadcast or multicast address,
since they are not really duplicates but replies from different hosts
to the same request.
.Pp
Damaged packets are obviously serious cause for alarm and often
indicate broken hardware somewhere in the
.Nm
packet's path (in the network or in the hosts).
.Sh 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 does not have sufficient
.Dq transitions ,
such as all ones or all zeros, or a pattern right at the edge, such as
almost all zeros.
It is not
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.
.Pp
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
cannot
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
.Fl p
option of
.Nm .
.Sh TTL DETAILS
The
.Tn 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
.Tn TTL
field by exactly one.
.Pp
The
.Tn TCP/IP
specification states that the
.Tn TTL
field for
.Tn TCP
packets should be set to 60, but many systems use smaller values
.No ( Bx 4.3
uses 30,
.Bx 4.2
used 15).
.Pp
The maximum possible value of this field is 255, and most
.Ux
systems set
the
.Tn TTL
field of
.Tn ICMP ECHO_REQUEST
packets to 255.
This is why you will find you can
.Dq ping
some hosts, but not reach them with
.Xr telnet 1
or
.Xr ftp 1 .
.Pp
In normal operation
.Nm
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
.Tn TTL
field in its response:
.Bl -bullet
.It
Not change it; this is what
.Bx
systems did before the
.Bx 4.3 tahoe
release.
In this case the
.Tn TTL
value in the received packet will be 255 minus the
number of routers in the round-trip path.
.It
Set it to 255; this is what current
.Bx
systems do.
In this case the
.Tn TTL
value in the received packet will be 255 minus the
number of routers in the path
.Em from
the remote system
.Em to
the
.Nm Ns Em ing
host.
.It
Set it to some other value.
Some machines use the same value for
.Tn ICMP
packets that they use for
.Tn TCP
packets, for example either 30 or 60.
Others may use completely wild values.
.El
.Sh RETURN VALUES
The
.Nm
utility returns an exit status of zero if at least one response was
heard from the specified
.Ar host ;
a status of two if the transmission was successful but no responses
were received; or another value
(from
.Aq Pa sysexits.h )
if an error occurred.
.Sh SEE ALSO
.Xr netstat 1 ,
.Xr ifconfig 8 ,
.Xr routed 8 ,
.Xr traceroute 8
.Sh HISTORY
The
.Nm
utility appeared in
.Bx 4.3 .
.Sh AUTHORS
The original
.Nm
utility was written by
.An Mike Muuss
while at the US Army Ballistics
Research Laboratory.
.Sh BUGS
Many Hosts and Gateways ignore the
.Tn RECORD_ROUTE
option.
.Pp
The maximum IP header length is too small for options like
.Tn RECORD_ROUTE
to be completely useful.
.No There Ap s
not much that can be done about this, however.
.Pp
Flood pinging is not recommended in general, and flood pinging the
broadcast address should only be done under very controlled conditions.
.Pp
The
.Fl v
option is not worth much on busy hosts.
|