1.\" Copyright (c) 1985, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)ping.8 8.2 (Berkeley) 12/11/93 33.\" $FreeBSD$ 34.\" 35.Dd September 25, 2001 36.Dt PING 8 37.Os 38.Sh NAME 39.Nm ping 40.Nd send 41.Tn ICMP ECHO_REQUEST 42packets to network hosts 43.Sh SYNOPSIS 44.Nm 45.Op Fl AQRadfnqrv 46.Op Fl c Ar count 47.Op Fl i Ar wait 48.Op Fl l Ar preload 49.Op Fl m Ar ttl 50.Op Fl p Ar pattern 51.Op Fl P Ar policy 52.Op Fl s Ar packetsize 53.Op Fl S Ar src_addr 54.Op Fl t Ar timeout 55.Bo 56.Ar host | 57.Op Fl L 58.Op Fl I Ar interface 59.Op Fl T Ar ttl 60.Ar mcast-group 61.Bc 62.Sh DESCRIPTION 63.Nm Ping 64uses the 65.Tn ICMP 66.No protocol Ap s mandatory 67.Tn ECHO_REQUEST 68datagram to elicit an 69.Tn ICMP ECHO_RESPONSE 70from a host or gateway. 71.Tn ECHO_REQUEST 72datagrams 73.Pq Dq pings 74have an IP and 75.Tn ICMP 76header, followed by a 77.Dq struct timeval 78and then an arbitrary number of 79.Dq pad 80bytes used to fill out the packet. The options are as follows: 81.Bl -tag -width indent 82.It Fl A 83Audible. 84Output a bell 85.Tn ( ASCII 860x07) 87character when no packet is received before the next packet 88is transmitted. 89To cater for round-trip times that are longer than the interval 90between transmissions, further missing packets cause a bell only 91if the maximum number of unreceived packets has increased. 92.It Fl a 93Audible. 94Include a bell 95.Tn ( ASCII 960x07) 97character in the output when any packet is received. 98This option is ignored 99if other format options are present. 100.It Fl c Ar count 101Stop after sending 102(and receiving) 103.Ar count 104.Tn ECHO_RESPONSE 105packets. 106If this option is not specified, 107.Nm 108will operate until interrupted. 109.It Fl d 110Set the 111.Dv SO_DEBUG 112option on the socket being used. 113.It Fl f 114Flood ping. 115Outputs packets as fast as they come back or one hundred times per second, 116whichever is more. 117For every 118.Tn ECHO_REQUEST 119sent a period 120.Dq .\& 121is printed, while for every 122.Tn ECHO_REPLY 123received a backspace is printed. 124This provides a rapid display of how many packets are being dropped. 125Only the super-user may use this option. 126.Bf -emphasis 127This can be very hard on a network and should be used with caution. 128.Ef 129.It Fl i Ar wait 130Wait 131.Ar wait 132seconds 133.Em between sending each packet . 134The default is to wait for one second between each packet. 135The wait time may be fractional, but only the super-user may specify 136values less then 1 second. 137This option is incompatible with the 138.Fl f 139option. 140.It Fl I Ar interface 141Source multicast packets with the given interface address. 142This flag only applies if the ping destination is a multicast address. 143.It Fl l Ar preload 144If 145.Ar preload 146is specified, 147.Nm 148sends that many packets as fast as possible before falling into its normal 149mode of behavior. 150Only the super-user may use this option. 151.It Fl m Ar ttl 152Set the IP Time To Live for outgoing packets. 153If not specified, the kernel uses the value of the 154.Va net.inet.ip.ttl 155MIB variable. 156.It Fl L 157Suppress loopback of multicast packets. 158This flag only applies if the ping destination is a multicast address. 159.It Fl n 160Numeric output only. 161No attempt will be made to lookup symbolic names for host addresses. 162.It Fl p Ar pattern 163You may specify up to 16 164.Dq pad 165bytes to fill out the packet you send. 166This is useful for diagnosing data-dependent problems in a network. 167For example, 168.Dq Li \-p ff 169will cause the sent packet to be filled with all 170ones. 171.It Fl P Ar policy 172.Ar policy 173specifies IPsec policy for the ping session. 174For details please refer to 175.Xr ipsec 4 176and 177.Xr ipsec_set_policy 3 . 178.It Fl Q 179Somewhat quiet output. 180.No Don Ap t 181display ICMP error messages that are in response to our query messages. 182Originally, the 183.Fl v 184flag was required to display such errors, but 185.Fl v 186displays all ICMP error messages. On a busy machine, this output can 187be overbearing. Without the 188.Fl Q 189flag, 190.Nm 191prints out any ICMP error messages caused by its own ECHO_REQUEST 192messages. 193.It Fl q 194Quiet output. 195Nothing is displayed except the summary lines at startup time and 196when finished. 197.It Fl R 198Record route. 199Includes the 200.Tn RECORD_ROUTE 201option in the 202.Tn ECHO_REQUEST 203packet and displays 204the route buffer on returned packets. 205Note that the IP header is only large enough for nine such routes; 206the 207.Xr traceroute 8 208command is usually better at determining the route packets take to a 209particular destination. 210If more routes come back than should, such as due to an illegal spoofed 211packet, ping will print the route list and then truncate it at the correct 212spot. 213Many hosts ignore or discard the 214.Tn RECORD_ROUTE 215option. 216.It Fl r 217Bypass the normal routing tables and send directly to a host on an attached 218network. 219If the host is not on a directly-attached network, an error is returned. 220This option can be used to ping a local host through an interface 221that has no route through it 222(e.g., after the interface was dropped by 223.Xr routed 8 ) . 224.It Fl s Ar packetsize 225Specify the number of data bytes to be sent. 226The default is 56, which translates into 64 227.Tn ICMP 228data bytes when combined 229with the 8 bytes of 230.Tn ICMP 231header data. 232Only the super-user may use this option. 233.It Fl S Ar src_addr 234Use the following IP address as the source address in outgoing packets. 235On hosts with more than one IP address, this option can be used to 236force the source address to be something other than the IP address 237of the interface the probe packet is sent on. If the IP address 238is not one of this machine's interface addresses, an error is 239returned and nothing is sent. 240.It Fl t Ar timeout 241Specify a timeout, in seconds, before ping exits regardless of how 242many packets have been recieved. 243.It Fl T Ar ttl 244Set the IP Time To Live for multicasted packets. 245This flag only applies if the ping destination is a multicast address. 246.It Fl v 247Verbose output. 248.Tn ICMP 249packets other than 250.Tn ECHO_RESPONSE 251that are received are listed. 252.El 253.Pp 254When using 255.Nm 256for fault isolation, it should first be run on the local host, to verify 257that the local network interface is up and running. 258Then, hosts and gateways further and further away should be 259.Dq pinged . 260Round-trip times and packet loss statistics are computed. 261If duplicate packets are received, they are not included in the packet 262loss calculation, although the round trip time of these packets is used 263in calculating the round-trip time statistics. 264When the specified number of packets have been sent 265(and received) 266or if the program is terminated with a 267.Dv SIGINT , 268a brief summary is displayed, showing the number of packets sent and 269received, and the minimum, maximum, mean, and standard deviation of 270the round-trip times. 271.Pp 272This program is intended for use in network testing, measurement and 273management. 274Because of the load it can impose on the network, it is unwise to use 275.Nm 276during normal operations or from automated scripts. 277.Sh ICMP PACKET DETAILS 278An IP header without options is 20 bytes. 279An 280.Tn ICMP 281.Tn ECHO_REQUEST 282packet contains an additional 8 bytes worth of 283.Tn ICMP 284header followed by an arbitrary amount of data. 285When a 286.Ar packetsize 287is given, this indicated the size of this extra piece of data 288(the default is 56). 289Thus the amount of data received inside of an IP packet of type 290.Tn ICMP 291.Tn ECHO_REPLY 292will always be 8 bytes more than the requested data space 293(the 294.Tn ICMP 295header). 296.Pp 297If the data space is at least eight bytes large, 298.Nm 299uses the first eight bytes of this space to include a timestamp which 300it uses in the computation of round trip times. 301If less than eight bytes of pad are specified, no round trip times are 302given. 303.Sh DUPLICATE AND DAMAGED PACKETS 304.Nm Ping 305will report duplicate and damaged packets. 306Duplicate packets should never occur when pinging a unicast address, 307and seem to be caused by 308inappropriate link-level retransmissions. 309Duplicates may occur in many situations and are rarely 310(if ever) 311a good sign, although the presence of low levels of duplicates may not 312always be cause for alarm. 313Duplicates are expected when pinging a broadcast or multicast address, 314since they are not really duplicates but replies from different hosts 315to the same request. 316.Pp 317Damaged packets are obviously serious cause for alarm and often 318indicate broken hardware somewhere in the 319.Nm 320packet's path (in the network or in the hosts). 321.Sh TRYING DIFFERENT DATA PATTERNS 322The 323(inter)network 324layer should never treat packets differently depending on the data 325contained in the data portion. 326Unfortunately, data-dependent problems have been known to sneak into 327networks and remain undetected for long periods of time. 328In many cases the particular pattern that will have problems is something 329that does not have sufficient 330.Dq transitions , 331such as all ones or all zeros, or a pattern right at the edge, such as 332almost all zeros. 333It is not 334necessarily enough to specify a data pattern of all zeros (for example) 335on the command line because the pattern that is of interest is 336at the data link level, and the relationship between what you type and 337what the controllers transmit can be complicated. 338.Pp 339This means that if you have a data-dependent problem you will probably 340have to do a lot of testing to find it. 341If you are lucky, you may manage to find a file that either 342cannot 343be sent across your network or that takes much longer to transfer than 344other similar length files. 345You can then examine this file for repeated patterns that you can test 346using the 347.Fl p 348option of 349.Nm . 350.Sh TTL DETAILS 351The 352.Tn TTL 353value of an IP packet represents the maximum number of IP routers 354that the packet can go through before being thrown away. 355In current practice you can expect each router in the Internet to decrement 356the 357.Tn TTL 358field by exactly one. 359.Pp 360The 361.Tn TCP/IP 362specification states that the 363.Tn TTL 364field for 365.Tn TCP 366packets should be set to 60, but many systems use smaller values 367.No ( Bx 4.3 368uses 30, 369.Bx 4.2 370used 15). 371.Pp 372The maximum possible value of this field is 255, and most 373.Ux 374systems set 375the 376.Tn TTL 377field of 378.Tn ICMP ECHO_REQUEST 379packets to 255. 380This is why you will find you can 381.Dq ping 382some hosts, but not reach them with 383.Xr telnet 1 384or 385.Xr ftp 1 . 386.Pp 387In normal operation 388.Nm 389prints the ttl value from the packet it receives. 390When a remote system receives a ping packet, it can do one of three things 391with the 392.Tn TTL 393field in its response: 394.Bl -bullet 395.It 396Not change it; this is what 397.Bx 398systems did before the 399.Bx 4.3 tahoe 400release. 401In this case the 402.Tn TTL 403value in the received packet will be 255 minus the 404number of routers in the round-trip path. 405.It 406Set it to 255; this is what current 407.Bx 408systems do. 409In this case the 410.Tn TTL 411value in the received packet will be 255 minus the 412number of routers in the path 413.Em from 414the remote system 415.Em to 416the 417.Nm Ns Em ing 418host. 419.It 420Set it to some other value. 421Some machines use the same value for 422.Tn ICMP 423packets that they use for 424.Tn TCP 425packets, for example either 30 or 60. 426Others may use completely wild values. 427.El 428.Sh RETURN VALUES 429The 430.Nm 431command returns an exit status of zero if at least one response was 432heard from the specified 433.Ar host ; 434a status of two if the transmission was successful but no responses 435were received; or another value 436(from 437.Aq Pa sysexits.h ) 438if an error occurred. 439.Sh SEE ALSO 440.Xr netstat 1 , 441.Xr ifconfig 8 , 442.Xr routed 8 , 443.Xr traceroute 8 444.Sh HISTORY 445The 446.Nm 447command appeared in 448.Bx 4.3 . 449.Sh AUTHORS 450The original 451.Nm 452command was written by 453.An Mike Muuss 454while at the US Army Ballistics 455Research Laboratory. 456.Sh BUGS 457Many Hosts and Gateways ignore the 458.Tn RECORD_ROUTE 459option. 460.Pp 461The maximum IP header length is too small for options like 462.Tn RECORD_ROUTE 463to be completely useful. 464.No There Ap s 465not much that can be done about this, however. 466.Pp 467Flood pinging is not recommended in general, and flood pinging the 468broadcast address should only be done under very controlled conditions. 469.Pp 470The 471.Fl v 472option is not worth much on busy hosts. 473