xref: /freebsd/sbin/ping/ping.8 (revision 380a989b3223d455375b4fae70fd0b9bdd43bafb)
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32.\"     @(#)ping.8	8.2 (Berkeley) 12/11/93
33.\"	$Id: ping.8,v 1.18 1998/11/29 13:20:04 bde Exp $
34.\"
35.Dd March 1, 1997
36.Dt PING 8
37.Os BSD 4.3
38.Sh NAME
39.Nm ping
40.Nd send
41.Tn ICMP ECHO_REQUEST
42packets to network hosts
43.Sh SYNOPSIS
44.Nm ping
45.Op Fl QRadfnqrv
46.Op Fl c Ar count
47.Op Fl i Ar wait
48.Op Fl l Ar preload
49.Op Fl p Ar pattern
50.Op Fl s Ar packetsize
51.Op Fl S Ar src_addr
52.Bo
53.Ar host |
54.Op Fl L
55.Op Fl I Ar interface
56.Op Fl T Ar ttl
57.Ar mcast-group
58.Bc
59.Sh DESCRIPTION
60.Nm Ping
61uses the
62.Tn ICMP
63.No protocol Ap s mandatory
64.Tn ECHO_REQUEST
65datagram to elicit an
66.Tn ICMP ECHO_RESPONSE
67from a host or gateway.
68.Tn ECHO_REQUEST
69datagrams
70.Pq Dq pings
71have an IP and
72.Tn ICMP
73header, followed by a
74.Dq struct timeval
75and then an arbitrary number of
76.Dq pad
77bytes used to fill out the packet.  The options are as follows:
78.Bl -tag -width indent
79.It Fl a
80Audible. Include a bell
81.Pq ASCII 0x07
82character in the output when any packet is received. This option is ignored
83if other format options are present.
84.It Fl c Ar count
85Stop after sending
86.Pq and receiving
87.Ar count
88.Tn ECHO_RESPONSE
89packets.
90If this option is not specified,
91.Nm
92will operate until interrupted.
93.It Fl d
94Set the
95.Dv SO_DEBUG
96option on the socket being used.
97.It Fl f
98Flood ping.
99Outputs packets as fast as they come back or one hundred times per second,
100whichever is more.
101For every
102.Tn ECHO_REQUEST
103sent a period
104.Dq \&.
105is printed, while for every
106.Tn ECHO_REPLY
107received a backspace is printed.
108This provides a rapid display of how many packets are being dropped.
109Only the super-user may use this option.
110.Bf -emphasis
111This can be very hard on a network and should be used with caution.
112.Ef
113.It Fl i Ar wait
114Wait
115.Ar wait
116seconds
117.Em between sending each packet .
118The default is to wait for one second between each packet.
119The wait time may be fractional, but only the super-user may specify
120values less then 1 second.
121This option is incompatible with the
122.Fl f
123option.
124.It Fl I Ar interface
125Source multicast packets with the given interface address.
126This flag only applies if the ping destination is a multicast address.
127.It Fl l Ar preload
128If
129.Ar preload
130is specified,
131.Nm
132sends that many packets as fast as possible before falling into its normal
133mode of behavior.
134Only the super-user may use this option.
135.It Fl L
136Suppress loopback of multicast packets.
137This flag only applies if the ping destination is a multicast address.
138.It Fl n
139Numeric output only.
140No attempt will be made to lookup symbolic names for host addresses.
141.It Fl p Ar pattern
142You may specify up to 16
143.Dq pad
144bytes to fill out the packet you send.
145This is useful for diagnosing data-dependent problems in a network.
146For example,
147.Dq Li \-p ff
148will cause the sent packet to be filled with all
149ones.
150.It Fl Q
151Somewhat quiet output.
152.No Don Ap t
153display ICMP error messages that are in response to our query messages.
154Originally, the
155.Fl v
156flag was required to display such errors, but
157.Fl v
158displays all ICMP error messages.  On a busy machine, this output can
159be overbearing.  Without the
160.Fl Q
161flag,
162.Nm
163prints out any ICMP error messages caused by its own ECHO_REQUEST
164messages.
165.It Fl q
166Quiet output.
167Nothing is displayed except the summary lines at startup time and
168when finished.
169.It Fl R
170Record route.
171Includes the
172.Tn RECORD_ROUTE
173option in the
174.Tn ECHO_REQUEST
175packet and displays
176the route buffer on returned packets.
177Note that the IP header is only large enough for nine such routes;
178the
179.Xr traceroute 8
180command is usually better at determining the route packets take to a
181particular destination.
182If more routes come back than should, such as due to an illegal spoofed
183packet, ping will print the route list and then truncate it at the correct
184spot.
185Many hosts ignore or discard the
186.Tn RECORD_ROUTE
187option.
188.It Fl r
189Bypass the normal routing tables and send directly to a host on an attached
190network.
191If the host is not on a directly-attached network, an error is returned.
192This option can be used to ping a local host through an interface
193that has no route through it
194.Po
195e.g., after the interface was dropped by
196.Xr routed 8
197.Pc .
198.It Fl s Ar packetsize
199Specify the number of data bytes to be sent.
200The default is 56, which translates into 64
201.Tn ICMP
202data bytes when combined
203with the 8 bytes of
204.Tn ICMP
205header data.
206Only the super-user may use this option.
207.It Fl T Ar ttl
208Set the IP Time To Live for multicasted packets.
209This flag only applies if the ping destination is a multicast address.
210.It Fl v
211Verbose output.
212.Tn ICMP
213packets other than
214.Tn ECHO_RESPONSE
215that are received are listed.
216.El
217.Pp
218When using
219.Nm
220for fault isolation, it should first be run on the local host, to verify
221that the local network interface is up and running.
222Then, hosts and gateways further and further away should be
223.Dq pinged .
224Round-trip times and packet loss statistics are computed.
225If duplicate packets are received, they are not included in the packet
226loss calculation, although the round trip time of these packets is used
227in calculating the round-trip time statistics.
228When the specified number of packets have been sent
229.Pq and received
230or if the program is terminated with a
231.Dv SIGINT ,
232a brief summary is displayed, showing the number of packets sent and
233received, and the minimum, maximum, mean, and standard deviation of
234the round-trip times.
235.Pp
236This program is intended for use in network testing, measurement and
237management.
238Because of the load it can impose on the network, it is unwise to use
239.Nm
240during normal operations or from automated scripts.
241.Sh ICMP PACKET DETAILS
242An IP header without options is 20 bytes.
243An
244.Tn ICMP
245.Tn ECHO_REQUEST
246packet contains an additional 8 bytes worth of
247.Tn ICMP
248header followed by an arbitrary amount of data.
249When a
250.Ar packetsize
251is given, this indicated the size of this extra piece of data
252.Pq the default is 56 .
253Thus the amount of data received inside of an IP packet of type
254.Tn ICMP
255.Tn ECHO_REPLY
256will always be 8 bytes more than the requested data space
257.Pq the Tn ICMP header .
258.Pp
259If the data space is at least eight bytes large,
260.Nm
261uses the first eight bytes of this space to include a timestamp which
262it uses in the computation of round trip times.
263If less than eight bytes of pad are specified, no round trip times are
264given.
265.Sh DUPLICATE AND DAMAGED PACKETS
266.Nm Ping
267will report duplicate and damaged packets.
268Duplicate packets should never occur when pinging a unicast address,
269and seem to be caused by
270inappropriate link-level retransmissions.
271Duplicates may occur in many situations and are rarely
272.Pq if ever
273a good sign, although the presence of low levels of duplicates may not
274always be cause for alarm.
275Duplicates are expected when pinging a broadcast or multicast address,
276since they are not really duplicates but replies from different hosts
277to the same request.
278.Pp
279Damaged packets are obviously serious cause for alarm and often
280indicate broken hardware somewhere in the
281.Nm
282packet's path (in the network or in the hosts).
283.Sh TRYING DIFFERENT DATA PATTERNS
284The
285(inter)network
286layer should never treat packets differently depending on the data
287contained in the data portion.
288Unfortunately, data-dependent problems have been known to sneak into
289networks and remain undetected for long periods of time.
290In many cases the particular pattern that will have problems is something
291that does not have sufficient
292.Dq transitions ,
293such as all ones or all zeros, or a pattern right at the edge, such as
294almost all zeros.
295It is not
296necessarily enough to specify a data pattern of all zeros (for example)
297on the command line because the pattern that is of interest is
298at the data link level, and the relationship between what you type and
299what the controllers transmit can be complicated.
300.Pp
301This means that if you have a data-dependent problem you will probably
302have to do a lot of testing to find it.
303If you are lucky, you may manage to find a file that either
304cannot
305be sent across your network or that takes much longer to transfer than
306other similar length files.
307You can then examine this file for repeated patterns that you can test
308using the
309.Fl p
310option of
311.Nm Ns .
312.Sh TTL DETAILS
313The
314.Tn TTL
315value of an IP packet represents the maximum number of IP routers
316that the packet can go through before being thrown away.
317In current practice you can expect each router in the Internet to decrement
318the
319.Tn TTL
320field by exactly one.
321.Pp
322The
323.Tn TCP/IP
324specification states that the
325.Tn TTL
326field for
327.Tn TCP
328packets should be set to 60, but many systems use smaller values
329.Po
330.Bx 4.3
331uses 30,
332.Bx 4.2
333used 15
334.Pc .
335.Pp
336The maximum possible value of this field is 255, and most
337.Ux
338systems set
339the
340.Tn TTL
341field of
342.Tn ICMP ECHO_REQUEST
343packets to 255.
344This is why you will find you can
345.Dq ping
346some hosts, but not reach them with
347.Xr telnet 1
348or
349.Xr ftp 1 .
350.Pp
351In normal operation
352.Nm
353prints the ttl value from the packet it receives.
354When a remote system receives a ping packet, it can do one of three things
355with the
356.Tn TTL
357field in its response:
358.Bl -bullet
359.It
360Not change it; this is what
361.Bx
362systems did before the
363.Bx 4.3 tahoe
364release.
365In this case the
366.Tn TTL
367value in the received packet will be 255 minus the
368number of routers in the round-trip path.
369.It
370Set it to 255; this is what current
371.Bx
372systems do.
373In this case the
374.Tn TTL
375value in the received packet will be 255 minus the
376number of routers in the path
377.Em from
378the remote system
379.Em to
380the
381.Nm Ns Em ing
382host.
383.It
384Set it to some other value.
385Some machines use the same value for
386.Tn ICMP
387packets that they use for
388.Tn TCP
389packets, for example either 30 or 60.
390Others may use completely wild values.
391.El
392.Sh RETURN VALUES
393The
394.Nm
395command returns an exit status of zero if at least one response was
396heard from the specified
397.Ar host ;
398a status of two if the transmission was successful but no responses
399were received; or another value
400.Pq from Aq Pa sysexits.h
401if an error occurred.
402.Sh SEE ALSO
403.Xr netstat 1 ,
404.Xr ifconfig 8 ,
405.Xr routed 8 ,
406.Xr traceroute 8
407.Sh HISTORY
408The
409.Nm
410command appeared in
411.Bx 4.3 .
412.Sh AUTHORS
413The original
414.Nm
415command was written by
416.An Mike Muuss
417while at the US Army Ballistics
418Research Laboratory.
419.Sh BUGS
420Many Hosts and Gateways ignore the
421.Tn RECORD_ROUTE
422option.
423.Pp
424The maximum IP header length is too small for options like
425.Tn RECORD_ROUTE
426to be completely useful.
427.No There Ap s
428not much that can be done about this, however.
429.Pp
430Flood pinging is not recommended in general, and flood pinging the
431broadcast address should only be done under very controlled conditions.
432.Pp
433The
434.Fl v
435option is not worth much on busy hosts.
436