ping.tproj/ping.8

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  32 .\"     @(#)ping.8      8.3 (Berkeley) 4/28/95
  33 .\"
  34 .Dd April 28, 1995
  35 .Dt PING 8
  36 .Os BSD 4.3
  37 .Sh NAME
  38 .Nm ping
  39 .Nd send
  40 .Tn ICMP ECHO_REQUEST
  41 packets to network hosts
  42 .Sh SYNOPSIS
  43 .Nm ping
  44 .Op Fl Rdfnqrv
  45 .Op Fl c Ar count
  46 .Op Fl i Ar wait
  47 .Op Fl l Ar preload
  48 .Op Fl p Ar pattern
  49 .Op Fl s Ar packetsize
  50 .Ar host
  51 .Sh DESCRIPTION
  52 .Nm Ping
  53 uses the
  54 .Tn ICMP
  55 protocol's mandatory
  56 .Tn ECHO_REQUEST
  57 datagram to elicit an
  58 .Tn ICMP ECHO_RESPONSE
  59 from a host or gateway.
  60 .Tn ECHO_REQUEST
  61 datagrams (``pings'') have an IP and
  62 .Tn ICMP
  63 header,
  64 followed by a
  65 .Dq struct timeval
  66 and then an arbitrary number of ``pad'' bytes used to fill out the
  67 packet.
  68 The options are as follows:
  69 .Bl -tag -width Ds
  70 .It Fl c Ar count
  71 Stop after sending (and receiving)
  72 .Ar count
  73 .Tn ECHO_RESPONSE
  74 packets.
  75 .It Fl d
  76 Set the
  77 .Dv SO_DEBUG
  78 option on the socket being used.
  79 .It Fl f
  80 Flood ping.
  81 Outputs packets as fast as they come back or one hundred times per second,
  82 whichever is more.
  83 For every
  84 .Tn ECHO_REQUEST
  85 sent a period ``.'' is printed, while for every
  86 .Tn ECHO_REPLY
  87 received a backspace is printed.
  88 This provides a rapid display of how many packets are being dropped.
  89 Only the super-user may use this option.
  90 .Bf -emphasis
  91 This can be very hard on a network and should be used with caution.
  92 .Ef
  93 .It Fl i Ar wait
  94 Wait
  95 .Ar wait
  96 seconds
  97 .Em between sending each packet .
  98 The default is to wait for one second between each packet.
  99 This option is incompatible with the
 100 .Fl f
 101 option.
 102 .It Fl l Ar preload
 103 If
 104 .Ar preload
 105 is specified,
 106 .Nm ping
 107 sends that many packets as fast as possible before falling into its normal
 108 mode of behavior.
 109 .It Fl n
 110 Numeric output only.
 111 No attempt will be made to lookup symbolic names for host addresses.
 112 .It Fl p Ar pattern
 113 You may specify up to 16 ``pad'' bytes to fill out the packet you send.
 114 This is useful for diagnosing data-dependent problems in a network.
 115 For example,
 116 .Dq Li \-p ff
 117 will cause the sent packet to be filled with all
 118 ones.
 119 .It Fl q
 120 Quiet output.
 121 Nothing is displayed except the summary lines at startup time and
 122 when finished.
 123 .It Fl R
 124 Record route.
 125 Includes the
 126 .Tn RECORD_ROUTE
 127 option in the
 128 .Tn ECHO_REQUEST
 129 packet and displays
 130 the route buffer on returned packets.
 131 Note that the IP header is only large enough for nine such routes.
 132 Many hosts ignore or discard this option.
 133 .It Fl r
 134 Bypass the normal routing tables and send directly to a host on an attached
 135 network.
 136 If the host is not on a directly-attached network, an error is returned.
 137 This option can be used to ping a local host through an interface
 138 that has no route through it (e.g., after the interface was dropped by
 139 .Xr routed 8 ) .
 140 .It Fl s Ar packetsize
 141 Specifies the number of data bytes to be sent.
 142 The default is 56, which translates into 64
 143 .Tn ICMP
 144 data bytes when combined
 145 with the 8 bytes of
 146 .Tn ICMP
 147 header data.
 148 .It Fl v
 149 Verbose output.
 150 .Tn ICMP
 151 packets other than
 152 .Tn ECHO_RESPONSE
 153 that are received are listed.
 154 .El
 155 .Pp
 156 When using
 157 .Nm ping
 158 for fault isolation, it should first be run on the local host, to verify
 159 that the local network interface is up and running.
 160 Then, hosts and gateways further and further away should be ``pinged''.
 161 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
 167 .Dv SIGINT ,
 168 a brief summary is displayed.
 169 .Pp
 170 This program is intended for use in network testing, measurement and
 171 management.
 172 Because of the load it can impose on the network, it is unwise to use
 173 .Nm ping
 174 during normal operations or from automated scripts.
 175 .Sh ICMP PACKET DETAILS
 176 An IP header without options is 20 bytes.
 177 An
 178 .Tn ICMP
 179 .Tn ECHO_REQUEST
 180 packet contains an additional 8 bytes worth
 181 of
 182 .Tn ICMP
 183 header followed by an arbitrary amount of data.
 184 When a
 185 .Ar packetsize
 186 is given, this indicated the size of this extra piece of data (the
 187 default is 56).
 188 Thus the amount of data received inside of an IP packet of type
 189 .Tn ICMP
 190 .Tn ECHO_REPLY
 191 will always be 8 bytes more than the requested data space
 192 (the
 193 .Tn ICMP
 194 header).
 195 .Pp
 196 If the data space is at least eight bytes large,
 197 .Nm ping
 198 uses the first eight bytes of this space to include a timestamp which
 199 it uses in the computation of round trip times.
 200 If less than eight bytes of pad are specified, no round trip times are
 201 given.
 202 .Sh DUPLICATE AND DAMAGED PACKETS
 203 .Nm Ping
 204 will report duplicate and damaged packets.
 205 Duplicate packets should never occur, and seem to be caused by
 206 inappropriate link-level retransmissions.
 207 Duplicates may occur in many situations and are rarely (if ever) a
 208 good sign, although the presence of low levels of duplicates may not
 209 always be cause for alarm.
 210 .Pp
 211 Damaged packets are obviously serious cause for alarm and often
 212 indicate broken hardware somewhere in the
 213 .Nm ping
 214 packet's path (in the network or in the hosts).
 215 .Sh TRYING DIFFERENT DATA PATTERNS
 216 The (inter)network layer should never treat packets differently depending
 217 on the data contained in the data portion.
 218 Unfortunately, data-dependent problems have been known to sneak into
 219 networks and remain undetected for long periods of time.
 220 In many cases the particular pattern that will have problems is something
 221 that doesn't have sufficient ``transitions'', such as all ones or all
 222 zeros, or a pattern right at the edge, such as almost all zeros.
 223 It isn't necessarily enough to specify a data pattern of all zeros (for
 224 example) on the command line because the pattern that is of interest is
 225 at the data link level, and the relationship between what you type and
 226 what the controllers transmit can be complicated.
 227 .Pp
 228 This means that if you have a data-dependent problem you will probably
 229 have to do a lot of testing to find it.
 230 If you are lucky, you may manage to find a file that either can't be sent
 231 across your network or that takes much longer to transfer than other
 232 similar length files.
 233 You can then examine this file for repeated patterns that you can test
 234 using the
 235 .Fl p
 236 option of
 237 .Nm ping .
 238 .Sh TTL DETAILS
 239 The
 240 .Tn TTL
 241 value of an IP packet represents the maximum number of IP routers
 242 that the packet can go through before being thrown away.
 243 In current practice you can expect each router in the Internet to decrement
 244 the
 245 .Tn TTL
 246 field by exactly one.
 247 .Pp
 248 The
 249 .Tn TCP/IP
 250 specification states that the
 251 .Tn TTL
 252 field for
 253 .Tn TCP
 254 packets should
 255 be set to 60, but many systems use smaller values (4.3
 256 .Tn BSD
 257 uses 30, 4.2 used
 258 15).
 259 .Pp
 260 The maximum possible value of this field is 255, and most Unix systems set
 261 the
 262 .Tn TTL
 263 field of
 264 .Tn ICMP ECHO_REQUEST
 265 packets to 255.
 266 This is why you will find you can ``ping'' some hosts, but not reach them
 267 with
 268 .Xr telnet 1
 269 or
 270 .Xr ftp 1 .
 271 .Pp
 272 In normal operation ping prints the ttl value from the packet it receives.
 273 When a remote system receives a ping packet, it can do one of three things
 274 with the
 275 .Tn TTL
 276 field in its response:
 277 .Bl -bullet
 278 .It
 279 Not change it; this is what Berkeley Unix systems did before the
 280 .Bx 4.3 tahoe
 281 release.
 282 In this case the
 283 .Tn TTL
 284 value in the received packet will be 255 minus the
 285 number of routers in the round-trip path.
 286 .It
 287 Set it to 255; this is what current Berkeley Unix systems do.
 288 In this case the
 289 .Tn TTL
 290 value in the received packet will be 255 minus the
 291 number of routers in the path
 292 .Xr from
 293 the remote system
 294 .Em to
 295 the
 296 .Nm ping Ns Em ing
 297 host.
 298 .It
 299 Set it to some other value.
 300 Some machines use the same value for
 301 .Tn ICMP
 302 packets that they use for
 303 .Tn TCP
 304 packets, for example either 30 or 60.
 305 Others may use completely wild values.
 306 .El
 307 .Sh BUGS
 308 Many Hosts and Gateways ignore the
 309 .Tn RECORD_ROUTE
 310 option.
 311 .Pp
 312 The maximum IP header length is too small for options like
 313 .Tn RECORD_ROUTE
 314 to
 315 be completely useful.
 316 There's not much that that can be done about this, however.
 317 .Pp
 318 Flood pinging is not recommended in general, and flood pinging the
 319 broadcast address should only be done under very controlled conditions.
 320 .Sh SEE ALSO
 321 .Xr netstat 1 ,
 322 .Xr ifconfig 8 ,
 323 .Xr routed 8
 324 .Sh HISTORY
 325 The
 326 .Nm
 327 command appeared in
 328 .Bx 4.3 .