1PING(8)                System Manager's Manual: iputils                PING(8)
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NAME

6       ping, ping6 - send ICMP ECHO_REQUEST to network hosts
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SYNOPSIS

9       ping  [ -LRUbdfnqrvVaAB]  [ -c count]  [ -i interval]  [ -l preload]  [
10       -p pattern]  [ -s packetsize]  [ -t ttl]  [ -w deadline]  [ -F  flowla‐
11       bel]   [ -I interface]  [ -M hint]  [ -Q tos]  [ -S sndbuf]  [ -T time‐
12       stamp option]  [ -W timeout]  [ hop ...]  destination
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14

DESCRIPTION

16       ping uses the ICMP protocol's mandatory ECHO_REQUEST datagram to elicit
17       an  ICMP  ECHO_RESPONSE from a host or gateway.  ECHO_REQUEST datagrams
18       (``pings'') have an IP and ICMP header, followed by  a  struct  timeval
19       and  then  an  arbitrary  number  of ``pad'' bytes used to fill out the
20       packet.
21

OPTIONS

23       -a     Audible ping.
24
25       -A     Adaptive ping. Interpacket interval adapts to  round-trip  time,
26              so  that  effectively  not more than one (or more, if preload is
27              set) unanswered probes present in the network. Minimal  interval
28              is  200msec  for  not super-user.  On networks with low rtt this
29              mode is essentially equivalent to flood mode.
30
31       -b     Allow pinging a broadcast address.
32
33       -B     Do not allow ping to  change  source  address  of  probes.   The
34              address is bound to one selected when ping starts.
35
36       -c count
37              Stop  after  sending  count  ECHO_REQUEST packets. With deadline
38              option, ping waits for count ECHO_REPLY packets, until the time‐
39              out expires.
40
41       -d     Set  the SO_DEBUG option on the socket being used.  Essentially,
42              this socket option is not used by Linux kernel.
43
44       -F flow label
45              Allocate and set 20 bit flow  label  on  echo  request  packets.
46              (Only  ping6).  If  value  is zero, kernel allocates random flow
47              label.
48
49       -f     Flood ping. For  every  ECHO_REQUEST  sent  a  period  ``.''  is
50              printed,  while  for  ever  ECHO_REPLY  received  a backspace is
51              printed.  This provides a rapid display of how many packets  are
52              being  dropped.   If  interval is not given, it sets interval to
53              zero and outputs packets as fast as they come back or  one  hun‐
54              dred  times  per second, whichever is more.  Only the super-user
55              may use this option with zero interval.
56
57       -i interval
58              Wait interval seconds between sending each packet.  The  default
59              is  to  wait for one second between each packet normally, or not
60              to wait in flood mode. Only super-user may set interval to  val‐
61              ues less 0.2 seconds.
62
63       -I interface address
64              Set  source address to specified interface address. Argument may
65              be numeric IP address or name of device. When pinging IPv6 link-
66              local address this option is required.
67
68       -l preload
69              If  preload is specified, ping sends that many packets not wait‐
70              ing for reply.  Only the super-user may select preload more than
71              3.
72
73       -L     Suppress  loopback of multicast packets.  This flag only applies
74              if the ping destination is a multicast address.
75
76       -n     Numeric output only.  No attempt will be made to lookup symbolic
77              names for host addresses.
78
79       -p pattern
80              You  may  specify  up to 16 ``pad'' bytes to fill out the packet
81              you send.  This is useful for diagnosing data-dependent problems
82              in  a network.  For example, -p ff will cause the sent packet to
83              be filled with all ones.
84
85       -Q tos Set Quality of Service -related bits in ICMP datagrams.  tos can
86              be either decimal or hex number.  Traditionally (RFC1349), these
87              have been interpreted as: 0 for reserved (currently being  rede‐
88              fined  as  congestion  control), 1-4 for Type of Service and 5-7
89              for Precedence.  Possible settings for Type of Service are: min‐
90              imal cost: 0x02, reliability: 0x04, throughput: 0x08, low delay:
91              0x10.  Multiple TOS bits should not be set simultaneously.  Pos‐
92              sible settings for special Precedence range from priority (0x20)
93              to net control (0xe0).  You must be root (CAP_NET_ADMIN capabil‐
94              ity) to use Critical or higher precedence value.  You cannot set
95              bit 0x01 (reserved) unless ECN has been enabled in  the  kernel.
96              In RFC2474, these fields has been redefined as 8-bit Differenti‐
97              ated Services (DS), consisting of: bits  0-1  of  separate  data
98              (ECN  will  be  used, here), and bits 2-7 of Differentiated Ser‐
99              vices Codepoint (DSCP).
100
101       -q     Quiet output.  Nothing is displayed except the summary lines  at
102              startup time and when finished.
103
104       -R     Record   route.    Includes   the  RECORD_ROUTE  option  in  the
105              ECHO_REQUEST packet and displays the route  buffer  on  returned
106              packets.   Note that the IP header is only large enough for nine
107              such routes.  Many hosts ignore or discard this option.
108
109       -r     Bypass the normal routing tables and send directly to a host  on
110              an  attached  interface.   If  the  host  is  not on a directly-
111              attached network, an error is returned.  This option can be used
112              to  ping  a  local  host  through an interface that has no route
113              through it provided the option -I is also used.
114
115       -s packetsize
116              Specifies the number of data bytes to be sent.  The  default  is
117              56,  which translates into 64 ICMP data bytes when combined with
118              the 8 bytes of ICMP header data.
119
120       -S sndbuf
121              Set socket sndbuf. If not specified, it is  selected  to  buffer
122              not more than one packet.
123
124       -t ttl Set the IP Time to Live.
125
126       -T timestamp option
127              Set  special  IP  timestamp  options.   timestamp  option may be
128              either  tsonly  (only  timestamps),  tsandaddr  (timestamps  and
129              addresses) or tsprespec host1 [host2 [host3 [host4]]] (timestamp
130              prespecified hops).
131
132       -M hint
133              Select Path MTU Discovery strategy.  hint may be either do (pro‐
134              hibit  fragmentation,  even local one), want (do PMTU discovery,
135              fragment locally when packet size is large), or dont (do not set
136              DF flag).
137
138       -U     Print  full  user-to-user  latency (the old behaviour). Normally
139              ping prints network round trip time, which can be different f.e.
140              due to DNS failures.
141
142       -v     Verbose output.
143
144       -V     Show version and exit.
145
146       -w deadline
147              Specify  a  timeout, in seconds, before ping exits regardless of
148              how many packets have been sent or received. In this  case  ping
149              does  not  stop after count packet are sent, it waits either for
150              deadline expire or until count probes are answered or  for  some
151              error notification from network.
152
153       -W timeout
154              Time to wait for a response, in seconds. The option affects only
155              timeout in absense of any responses, otherwise  ping  waits  for
156              two RTTs.
157
158       When  using  ping  for  fault  isolation, it should first be run on the
159       local host, to verify that the local network interface is up  and  run‐
160       ning.  Then,  hosts  and  gateways  further  and further away should be
161       ``pinged''. Round-trip times and packet loss statistics  are  computed.
162       If  duplicate packets are received, they are not included in the packet
163       loss calculation, although the round trip time of these packets is used
164       in  calculating  the  minimum/average/maximum  round-trip time numbers.
165       When the specified number of packets have been sent (and  received)  or
166       if  the  program  is  terminated with a SIGINT, a brief summary is dis‐
167       played. Shorter current statistics can be obtained without  termination
168       of process with signal SIGQUIT.
169
170       If  ping  does  not  receive any reply packets at all it will exit with
171       code 1. If a packet count and deadline are both  specified,  and  fewer
172       than  count  packets are received by the time the deadline has arrived,
173       it will also exit with code 1.  On other error it exits  with  code  2.
174       Otherwise  it exits with code 0. This makes it possible to use the exit
175       code to see if a host is alive or not.
176
177       This program is intended for use in network  testing,  measurement  and
178       management.   Because  of  the load it can impose on the network, it is
179       unwise to use ping during normal operations or from automated scripts.
180

ICMP PACKET DETAILS

182       An IP header without options is 20 bytes.  An ICMP ECHO_REQUEST  packet
183       contains  an  additional  8  bytes  worth of ICMP header followed by an
184       arbitrary amount of data.  When a packetsize is given,  this  indicated
185       the  size  of  this  extra  piece of data (the default is 56). Thus the
186       amount of data received inside of an IP packet of type ICMP  ECHO_REPLY
187       will  always  be  8  bytes more than the requested data space (the ICMP
188       header).
189
190       If the data space is at least of size of struct timeval ping  uses  the
191       beginning  bytes  of this space to include a timestamp which it uses in
192       the computation of round trip times.  If the data space is shorter,  no
193       round trip times are given.
194

DUPLICATE AND DAMAGED PACKETS

196       ping  will  report  duplicate  and  damaged packets.  Duplicate packets
197       should never occur, and seem to be caused by  inappropriate  link-level
198       retransmissions.   Duplicates  may  occur  in  many  situations and are
199       rarely (if ever) a good sign, although the presence of  low  levels  of
200       duplicates may not always be cause for alarm.
201
202       Damaged  packets  are obviously serious cause for alarm and often indi‐
203       cate broken hardware somewhere in the ping packet's path (in  the  net‐
204       work or in the hosts).
205

TRYING DIFFERENT DATA PATTERNS

207       The (inter)network layer should never treat packets differently depend‐
208       ing on the data contained in the data  portion.   Unfortunately,  data-
209       dependent  problems  have  been known to sneak into networks and remain
210       undetected for long periods of time.  In many cases the particular pat‐
211       tern  that will have problems is something that doesn't have sufficient
212       ``transitions'', such as all ones or all zeros, or a pattern  right  at
213       the  edge,  such  as  almost all zeros.  It isn't necessarily enough to
214       specify a data pattern of all zeros (for example) on the  command  line
215       because  the pattern that is of interest is at the data link level, and
216       the relationship between what you type and what the controllers  trans‐
217       mit can be complicated.
218
219       This  means that if you have a data-dependent problem you will probably
220       have to do a lot of testing to find it.  If you are lucky, you may man‐
221       age  to  find  a  file that either can't be sent across your network or
222       that takes much longer to transfer than  other  similar  length  files.
223       You  can then examine this file for repeated patterns that you can test
224       using the -p option of ping.
225

TTL DETAILS

227       The TTL value of an IP packet  represents  the  maximum  number  of  IP
228       routers  that  the  packet can go through before being thrown away.  In
229       current practice you can expect each router in the Internet  to  decre‐
230       ment the TTL field by exactly one.
231
232       The  TCP/IP  specification  states  that  the TTL field for TCP packets
233       should be set to 60, but many systems use smaller values (4.3 BSD  uses
234       30, 4.2 used 15).
235
236       The  maximum possible value of this field is 255, and most Unix systems
237       set the TTL field of ICMP ECHO_REQUEST packets to 255.  This is why you
238       will  find  you  can  ``ping'' some hosts, but not reach them with tel‐
239       net(1) or ftp(1).
240
241       In normal operation ping prints  the  ttl  value  from  the  packet  it
242       receives.   When  a remote system receives a ping packet, it can do one
243       of three things with the TTL field in its response:
244
245       · Not change it; this is what Berkeley  Unix  systems  did  before  the
246         4.3BSD  Tahoe  release.  In  this  case the TTL value in the received
247         packet will be 255 minus the number  of  routers  in  the  round-trip
248         path.
249
250       · Set  it  to  255;  this is what current Berkeley Unix systems do.  In
251         this case the TTL value in the received packet will be 255 minus  the
252         number  of  routers in the path from the remote system to the pinging
253         host.
254
255       · Set it to some other value. Some machines use the same value for ICMP
256         packets  that  they use for TCP packets, for example either 30 or 60.
257         Others may use completely wild values.
258

BUGS

260       · Many Hosts and Gateways ignore the RECORD_ROUTE option.
261
262       · The  maximum  IP  header  length  is  too  small  for  options   like
263         RECORD_ROUTE to be completely useful.  There's not much that that can
264         be done about this, however.
265
266       · Flood pinging is not recommended in general, and  flood  pinging  the
267         broadcast  address  should  only be done under very controlled condi‐
268         tions.
269

SEE ALSO

271       netstat(1), ifconfig(8).
272

HISTORY

274       The ping command appeared in 4.3BSD.
275
276       The version described here is its descendant specific to Linux.
277

SECURITY

279       ping requires CAP_NET_RAWIO capability to be executed. It may  be  used
280       as set-uid root.
281

AVAILABILITY

283       ping  is part of iputils package and the latest versions are  available
284       in   source    form    at    http://www.skbuff.net/iputils/iputils-cur
285       rent.tar.bz2.
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289iputils-071127                   22 March 2017                         PING(8)
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