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 October 2, 2002 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 AQRadfnoqrv 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 63The 64.Nm 65utility uses the 66.Tn ICMP 67.No protocol Ap s mandatory 68.Tn ECHO_REQUEST 69datagram to elicit an 70.Tn ICMP ECHO_RESPONSE 71from a host or gateway. 72.Tn ECHO_REQUEST 73datagrams 74.Pq Dq pings 75have an IP and 76.Tn ICMP 77header, followed by a 78.Dq struct timeval 79and then an arbitrary number of 80.Dq pad 81bytes used to fill out the packet. The options are as follows: 82.Bl -tag -width indent 83.It Fl A 84Audible. 85Output a bell 86.Tn ( ASCII 870x07) 88character when no packet is received before the next packet 89is transmitted. 90To cater for round-trip times that are longer than the interval 91between transmissions, further missing packets cause a bell only 92if the maximum number of unreceived packets has increased. 93.It Fl a 94Audible. 95Include a bell 96.Tn ( ASCII 970x07) 98character in the output when any packet is received. 99This option is ignored 100if other format options are present. 101.It Fl c Ar count 102Stop after sending 103(and receiving) 104.Ar count 105.Tn ECHO_RESPONSE 106packets. 107If this option is not specified, 108.Nm 109will operate until interrupted. 110.It Fl d 111Set the 112.Dv SO_DEBUG 113option on the socket being used. 114.It Fl f 115Flood ping. 116Outputs packets as fast as they come back or one hundred times per second, 117whichever is more. 118For every 119.Tn ECHO_REQUEST 120sent a period 121.Dq .\& 122is printed, while for every 123.Tn ECHO_REPLY 124received a backspace is printed. 125This provides a rapid display of how many packets are being dropped. 126Only the super-user may use this option. 127.Bf -emphasis 128This can be very hard on a network and should be used with caution. 129.Ef 130.It Fl i Ar wait 131Wait 132.Ar wait 133seconds 134.Em between sending each packet . 135The default is to wait for one second between each packet. 136The wait time may be fractional, but only the super-user may specify 137values less then 1 second. 138This option is incompatible with the 139.Fl f 140option. 141.It Fl I Ar interface 142Source multicast packets with the given interface address. 143This flag only applies if the ping destination is a multicast address. 144.It Fl l Ar preload 145If 146.Ar preload 147is specified, 148.Nm 149sends that many packets as fast as possible before falling into its normal 150mode of behavior. 151Only the super-user may use this option. 152.It Fl m Ar ttl 153Set the IP Time To Live for outgoing packets. 154If not specified, the kernel uses the value of the 155.Va net.inet.ip.ttl 156MIB variable. 157.It Fl L 158Suppress loopback of multicast packets. 159This flag only applies if the ping destination is a multicast address. 160.It Fl n 161Numeric output only. 162No attempt will be made to lookup symbolic names for host addresses. 163.It Fl o 164Exit successfully after receiving one reply packet. 165.It Fl p Ar pattern 166You may specify up to 16 167.Dq pad 168bytes to fill out the packet you send. 169This is useful for diagnosing data-dependent problems in a network. 170For example, 171.Dq Li \-p ff 172will cause the sent packet to be filled with all 173ones. 174.It Fl P Ar policy 175.Ar policy 176specifies IPsec policy for the ping session. 177For details please refer to 178.Xr ipsec 4 179and 180.Xr ipsec_set_policy 3 . 181.It Fl Q 182Somewhat quiet output. 183.No Don Ap t 184display ICMP error messages that are in response to our query messages. 185Originally, the 186.Fl v 187flag was required to display such errors, but 188.Fl v 189displays all ICMP error messages. On a busy machine, this output can 190be overbearing. Without the 191.Fl Q 192flag, 193.Nm 194prints out any ICMP error messages caused by its own ECHO_REQUEST 195messages. 196.It Fl q 197Quiet output. 198Nothing is displayed except the summary lines at startup time and 199when finished. 200.It Fl R 201Record route. 202Includes the 203.Tn RECORD_ROUTE 204option in the 205.Tn ECHO_REQUEST 206packet and displays 207the route buffer on returned packets. 208Note that the IP header is only large enough for nine such routes; 209the 210.Xr traceroute 8 211command is usually better at determining the route packets take to a 212particular destination. 213If more routes come back than should, such as due to an illegal spoofed 214packet, ping will print the route list and then truncate it at the correct 215spot. 216Many hosts ignore or discard the 217.Tn RECORD_ROUTE 218option. 219.It Fl r 220Bypass the normal routing tables and send directly to a host on an attached 221network. 222If the host is not on a directly-attached network, an error is returned. 223This option can be used to ping a local host through an interface 224that has no route through it 225(e.g., after the interface was dropped by 226.Xr routed 8 ) . 227.It Fl s Ar packetsize 228Specify the number of data bytes to be sent. 229The default is 56, which translates into 64 230.Tn ICMP 231data bytes when combined 232with the 8 bytes of 233.Tn ICMP 234header data. 235Only the super-user may use this option. 236.It Fl S Ar src_addr 237Use the following IP address as the source address in outgoing packets. 238On hosts with more than one IP address, this option can be used to 239force the source address to be something other than the IP address 240of the interface the probe packet is sent on. If the IP address 241is not one of this machine's interface addresses, an error is 242returned and nothing is sent. 243.It Fl t Ar timeout 244Specify a timeout, in seconds, before ping exits regardless of how 245many packets have been recieved. 246.It Fl T Ar ttl 247Set the IP Time To Live for multicasted packets. 248This flag only applies if the ping destination is a multicast address. 249.It Fl v 250Verbose output. 251.Tn ICMP 252packets other than 253.Tn ECHO_RESPONSE 254that are received are listed. 255.El 256.Pp 257When using 258.Nm 259for fault isolation, it should first be run on the local host, to verify 260that the local network interface is up and running. 261Then, hosts and gateways further and further away should be 262.Dq pinged . 263Round-trip times and packet loss statistics are computed. 264If duplicate packets are received, they are not included in the packet 265loss calculation, although the round trip time of these packets is used 266in calculating the round-trip time statistics. 267When the specified number of packets have been sent 268(and received) 269or if the program is terminated with a 270.Dv SIGINT , 271a brief summary is displayed, showing the number of packets sent and 272received, and the minimum, mean, maximum, and standard deviation of 273the round-trip times. 274.Pp 275If 276.Nm 277receives a 278.Dv SIGINFO 279(see the 280.Cm status 281argument for 282.Xr stty 1 ) 283signal, the current number of packets sent and received, and the 284minimum, mean, and maximum of the round-trip times will be written to 285the standard error output. 286.Pp 287This program is intended for use in network testing, measurement and 288management. 289Because of the load it can impose on the network, it is unwise to use 290.Nm 291during normal operations or from automated scripts. 292.Sh ICMP PACKET DETAILS 293An IP header without options is 20 bytes. 294An 295.Tn ICMP 296.Tn ECHO_REQUEST 297packet contains an additional 8 bytes worth of 298.Tn ICMP 299header followed by an arbitrary amount of data. 300When a 301.Ar packetsize 302is given, this indicated the size of this extra piece of data 303(the default is 56). 304Thus the amount of data received inside of an IP packet of type 305.Tn ICMP 306.Tn ECHO_REPLY 307will always be 8 bytes more than the requested data space 308(the 309.Tn ICMP 310header). 311.Pp 312If the data space is at least eight bytes large, 313.Nm 314uses the first eight bytes of this space to include a timestamp which 315it uses in the computation of round trip times. 316If less than eight bytes of pad are specified, no round trip times are 317given. 318.Sh DUPLICATE AND DAMAGED PACKETS 319The 320.Nm 321utility will report duplicate and damaged packets. 322Duplicate packets should never occur when pinging a unicast address, 323and seem to be caused by 324inappropriate link-level retransmissions. 325Duplicates may occur in many situations and are rarely 326(if ever) 327a good sign, although the presence of low levels of duplicates may not 328always be cause for alarm. 329Duplicates are expected when pinging a broadcast or multicast address, 330since they are not really duplicates but replies from different hosts 331to the same request. 332.Pp 333Damaged packets are obviously serious cause for alarm and often 334indicate broken hardware somewhere in the 335.Nm 336packet's path (in the network or in the hosts). 337.Sh TRYING DIFFERENT DATA PATTERNS 338The 339(inter)network 340layer should never treat packets differently depending on the data 341contained in the data portion. 342Unfortunately, data-dependent problems have been known to sneak into 343networks and remain undetected for long periods of time. 344In many cases the particular pattern that will have problems is something 345that does not have sufficient 346.Dq transitions , 347such as all ones or all zeros, or a pattern right at the edge, such as 348almost all zeros. 349It is not 350necessarily enough to specify a data pattern of all zeros (for example) 351on the command line because the pattern that is of interest is 352at the data link level, and the relationship between what you type and 353what the controllers transmit can be complicated. 354.Pp 355This means that if you have a data-dependent problem you will probably 356have to do a lot of testing to find it. 357If you are lucky, you may manage to find a file that either 358cannot 359be sent across your network or that takes much longer to transfer than 360other similar length files. 361You can then examine this file for repeated patterns that you can test 362using the 363.Fl p 364option of 365.Nm . 366.Sh TTL DETAILS 367The 368.Tn TTL 369value of an IP packet represents the maximum number of IP routers 370that the packet can go through before being thrown away. 371In current practice you can expect each router in the Internet to decrement 372the 373.Tn TTL 374field by exactly one. 375.Pp 376The 377.Tn TCP/IP 378specification states that the 379.Tn TTL 380field for 381.Tn TCP 382packets should be set to 60, but many systems use smaller values 383.No ( Bx 4.3 384uses 30, 385.Bx 4.2 386used 15). 387.Pp 388The maximum possible value of this field is 255, and most 389.Ux 390systems set 391the 392.Tn TTL 393field of 394.Tn ICMP ECHO_REQUEST 395packets to 255. 396This is why you will find you can 397.Dq ping 398some hosts, but not reach them with 399.Xr telnet 1 400or 401.Xr ftp 1 . 402.Pp 403In normal operation 404.Nm 405prints the ttl value from the packet it receives. 406When a remote system receives a ping packet, it can do one of three things 407with the 408.Tn TTL 409field in its response: 410.Bl -bullet 411.It 412Not change it; this is what 413.Bx 414systems did before the 415.Bx 4.3 tahoe 416release. 417In this case the 418.Tn TTL 419value in the received packet will be 255 minus the 420number of routers in the round-trip path. 421.It 422Set it to 255; this is what current 423.Bx 424systems do. 425In this case the 426.Tn TTL 427value in the received packet will be 255 minus the 428number of routers in the path 429.Em from 430the remote system 431.Em to 432the 433.Nm Ns Em ing 434host. 435.It 436Set it to some other value. 437Some machines use the same value for 438.Tn ICMP 439packets that they use for 440.Tn TCP 441packets, for example either 30 or 60. 442Others may use completely wild values. 443.El 444.Sh RETURN VALUES 445The 446.Nm 447utility returns an exit status of zero if at least one response was 448heard from the specified 449.Ar host ; 450a status of two if the transmission was successful but no responses 451were received; or another value 452(from 453.Aq Pa sysexits.h ) 454if an error occurred. 455.Sh SEE ALSO 456.Xr netstat 1 , 457.Xr ifconfig 8 , 458.Xr routed 8 , 459.Xr traceroute 8 460.Sh HISTORY 461The 462.Nm 463utility appeared in 464.Bx 4.3 . 465.Sh AUTHORS 466The original 467.Nm 468utility was written by 469.An Mike Muuss 470while at the US Army Ballistics 471Research Laboratory. 472.Sh BUGS 473Many Hosts and Gateways ignore the 474.Tn RECORD_ROUTE 475option. 476.Pp 477The maximum IP header length is too small for options like 478.Tn RECORD_ROUTE 479to be completely useful. 480.No There Ap s 481not much that can be done about this, however. 482.Pp 483Flood pinging is not recommended in general, and flood pinging the 484broadcast address should only be done under very controlled conditions. 485.Pp 486The 487.Fl v 488option is not worth much on busy hosts. 489