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.\" 4. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)ping.8 8.2 (Berkeley) 12/11/93 29.\" $FreeBSD$ 30.\" 31.Dd October 2, 2002 32.Dt PING 8 33.Os 34.Sh NAME 35.Nm ping 36.Nd send 37.Tn ICMP ECHO_REQUEST 38packets to network hosts 39.Sh SYNOPSIS 40.Nm 41.Op Fl AaDdfnoQqRrv 42.Op Fl c Ar count 43.Op Fl i Ar wait 44.Op Fl l Ar preload 45.Op Fl M Cm mask | time 46.Op Fl m Ar ttl 47.Op Fl P Ar policy 48.Op Fl p Ar pattern 49.Op Fl S Ar src_addr 50.Op Fl s Ar packetsize 51.Op Fl t Ar timeout 52.Op Fl z Ar tos 53.Ar host 54.Nm 55.Op Fl AaDdfLnoQqRrv 56.Op Fl c Ar count 57.Op Fl I Ar iface 58.Op Fl i Ar wait 59.Op Fl l Ar preload 60.Op Fl M Cm mask | time 61.Op Fl m Ar ttl 62.Op Fl P Ar policy 63.Op Fl p Ar pattern 64.Op Fl S Ar src_addr 65.Op Fl s Ar packetsize 66.Op Fl T Ar ttl 67.Op Fl t Ar timeout 68.Op Fl z Ar tos 69.Ar mcast-group 70.Sh DESCRIPTION 71The 72.Nm 73utility uses the 74.Tn ICMP 75.No protocol Ap s mandatory 76.Tn ECHO_REQUEST 77datagram to elicit an 78.Tn ICMP ECHO_RESPONSE 79from a host or gateway. 80.Tn ECHO_REQUEST 81datagrams 82.Pq Dq pings 83have an IP and 84.Tn ICMP 85header, followed by a 86.Dq struct timeval 87and then an arbitrary number of 88.Dq pad 89bytes used to fill out the packet. 90The options are as follows: 91.Bl -tag -width indent 92.It Fl A 93Audible. 94Output a bell 95.Tn ( ASCII 960x07) 97character when no packet is received before the next packet 98is transmitted. 99To cater for round-trip times that are longer than the interval 100between transmissions, further missing packets cause a bell only 101if the maximum number of unreceived packets has increased. 102.It Fl a 103Audible. 104Include a bell 105.Tn ( ASCII 1060x07) 107character in the output when any packet is received. 108This option is ignored 109if other format options are present. 110.It Fl c Ar count 111Stop after sending 112(and receiving) 113.Ar count 114.Tn ECHO_RESPONSE 115packets. 116If this option is not specified, 117.Nm 118will operate until interrupted. 119.It Fl D 120Set the Don't Fragment bit. 121.It Fl d 122Set the 123.Dv SO_DEBUG 124option on the socket being used. 125.It Fl f 126Flood ping. 127Outputs packets as fast as they come back or one hundred times per second, 128whichever is more. 129For every 130.Tn ECHO_REQUEST 131sent a period 132.Dq .\& 133is printed, while for every 134.Tn ECHO_REPLY 135received a backspace is printed. 136This provides a rapid display of how many packets are being dropped. 137Only the super-user may use this option. 138.Bf -emphasis 139This can be very hard on a network and should be used with caution. 140.Ef 141.It Fl I Ar iface 142Source multicast packets with the given interface address. 143This flag only applies if the ping destination is a multicast address. 144.It Fl i Ar wait 145Wait 146.Ar wait 147seconds 148.Em between sending each packet . 149The default is to wait for one second between each packet. 150The wait time may be fractional, but only the super-user may specify 151values less than 1 second. 152This option is incompatible with the 153.Fl f 154option. 155.It Fl L 156Suppress loopback of multicast packets. 157This flag only applies if the ping destination is a multicast address. 158.It Fl l Ar preload 159If 160.Ar preload 161is specified, 162.Nm 163sends that many packets as fast as possible before falling into its normal 164mode of behavior. 165Only the super-user may use this option. 166.It Fl M Cm mask | time 167Use 168.Dv ICMP_MASKREQ 169or 170.Dv ICMP_TSTAMP 171instead of 172.Dv ICMP_ECHO . 173For 174.Cm mask , 175print the netmask of the remote machine. 176Set the 177.Va net.inet.icmp.maskrepl 178MIB variable to enable 179.Dv ICMP_MASKREPLY . 180For 181.Cm time , 182print the origination, reception and transmission timestamps. 183.It Fl m Ar ttl 184Set the IP Time To Live for outgoing packets. 185If not specified, the kernel uses the value of the 186.Va net.inet.ip.ttl 187MIB variable. 188.It Fl n 189Numeric output only. 190No attempt will be made to lookup symbolic names for host addresses. 191.It Fl o 192Exit successfully after receiving one reply packet. 193.It Fl P Ar policy 194.Ar policy 195specifies IPsec policy for the ping session. 196For details please refer to 197.Xr ipsec 4 198and 199.Xr ipsec_set_policy 3 . 200.It Fl p Ar pattern 201You may specify up to 16 202.Dq pad 203bytes to fill out the packet you send. 204This is useful for diagnosing data-dependent problems in a network. 205For example, 206.Dq Li \-p ff 207will cause the sent packet to be filled with all 208ones. 209.It Fl Q 210Somewhat quiet output. 211.No Don Ap t 212display ICMP error messages that are in response to our query messages. 213Originally, the 214.Fl v 215flag was required to display such errors, but 216.Fl v 217displays all ICMP error messages. 218On a busy machine, this output can be overbearing. 219Without the 220.Fl Q 221flag, 222.Nm 223prints out any ICMP error messages caused by its own ECHO_REQUEST 224messages. 225.It Fl q 226Quiet output. 227Nothing is displayed except the summary lines at startup time and 228when finished. 229.It Fl R 230Record route. 231Includes the 232.Tn RECORD_ROUTE 233option in the 234.Tn ECHO_REQUEST 235packet and displays 236the route buffer on returned packets. 237Note that the IP header is only large enough for nine such routes; 238the 239.Xr traceroute 8 240command is usually better at determining the route packets take to a 241particular destination. 242If more routes come back than should, such as due to an illegal spoofed 243packet, ping will print the route list and then truncate it at the correct 244spot. 245Many hosts ignore or discard the 246.Tn RECORD_ROUTE 247option. 248.It Fl r 249Bypass the normal routing tables and send directly to a host on an attached 250network. 251If the host is not on a directly-attached network, an error is returned. 252This option can be used to ping a local host through an interface 253that has no route through it 254(e.g., after the interface was dropped by 255.Xr routed 8 ) . 256.It Fl S Ar src_addr 257Use the following IP address as the source address in outgoing packets. 258On hosts with more than one IP address, this option can be used to 259force the source address to be something other than the IP address 260of the interface the probe packet is sent on. 261If the IP address 262is not one of this machine's interface addresses, an error is 263returned and nothing is sent. 264.It Fl s Ar packetsize 265Specify the number of data bytes to be sent. 266The default is 56, which translates into 64 267.Tn ICMP 268data bytes when combined 269with the 8 bytes of 270.Tn ICMP 271header data. 272Only the super-user may specify values more than default. 273.It Fl T Ar ttl 274Set the IP Time To Live for multicasted packets. 275This flag only applies if the ping destination is a multicast address. 276.It Fl t Ar timeout 277Specify a timeout, in seconds, before ping exits regardless of how 278many packets have been received. 279.It Fl v 280Verbose output. 281.Tn ICMP 282packets other than 283.Tn ECHO_RESPONSE 284that are received are listed. 285.It Fl z Ar tos 286Use the specified type of service. 287.El 288.Pp 289When using 290.Nm 291for fault isolation, it should first be run on the local host, to verify 292that the local network interface is up and running. 293Then, hosts and gateways further and further away should be 294.Dq pinged . 295Round-trip times and packet loss statistics are computed. 296If duplicate packets are received, they are not included in the packet 297loss calculation, although the round trip time of these packets is used 298in calculating the round-trip time statistics. 299When the specified number of packets have been sent 300(and received) 301or if the program is terminated with a 302.Dv SIGINT , 303a brief summary is displayed, showing the number of packets sent and 304received, and the minimum, mean, maximum, and standard deviation of 305the round-trip times. 306.Pp 307If 308.Nm 309receives a 310.Dv SIGINFO 311(see the 312.Cm status 313argument for 314.Xr stty 1 ) 315signal, the current number of packets sent and received, and the 316minimum, mean, and maximum of the round-trip times will be written to 317the standard error output. 318.Pp 319This program is intended for use in network testing, measurement and 320management. 321Because of the load it can impose on the network, it is unwise to use 322.Nm 323during normal operations or from automated scripts. 324.Sh ICMP PACKET DETAILS 325An IP header without options is 20 bytes. 326An 327.Tn ICMP 328.Tn ECHO_REQUEST 329packet contains an additional 8 bytes worth of 330.Tn ICMP 331header followed by an arbitrary amount of data. 332When a 333.Ar packetsize 334is given, this indicated the size of this extra piece of data 335(the default is 56). 336Thus the amount of data received inside of an IP packet of type 337.Tn ICMP 338.Tn ECHO_REPLY 339will always be 8 bytes more than the requested data space 340(the 341.Tn ICMP 342header). 343.Pp 344If the data space is at least eight bytes large, 345.Nm 346uses the first eight bytes of this space to include a timestamp which 347it uses in the computation of round trip times. 348If less than eight bytes of pad are specified, no round trip times are 349given. 350.Sh DUPLICATE AND DAMAGED PACKETS 351The 352.Nm 353utility will report duplicate and damaged packets. 354Duplicate packets should never occur when pinging a unicast address, 355and seem to be caused by 356inappropriate link-level retransmissions. 357Duplicates may occur in many situations and are rarely 358(if ever) 359a good sign, although the presence of low levels of duplicates may not 360always be cause for alarm. 361Duplicates are expected when pinging a broadcast or multicast address, 362since they are not really duplicates but replies from different hosts 363to the same request. 364.Pp 365Damaged packets are obviously serious cause for alarm and often 366indicate broken hardware somewhere in the 367.Nm 368packet's path (in the network or in the hosts). 369.Sh TRYING DIFFERENT DATA PATTERNS 370The 371(inter)network 372layer should never treat packets differently depending on the data 373contained in the data portion. 374Unfortunately, data-dependent problems have been known to sneak into 375networks and remain undetected for long periods of time. 376In many cases the particular pattern that will have problems is something 377that does not have sufficient 378.Dq transitions , 379such as all ones or all zeros, or a pattern right at the edge, such as 380almost all zeros. 381It is not 382necessarily enough to specify a data pattern of all zeros (for example) 383on the command line because the pattern that is of interest is 384at the data link level, and the relationship between what you type and 385what the controllers transmit can be complicated. 386.Pp 387This means that if you have a data-dependent problem you will probably 388have to do a lot of testing to find it. 389If you are lucky, you may manage to find a file that either 390cannot 391be sent across your network or that takes much longer to transfer than 392other similar length files. 393You can then examine this file for repeated patterns that you can test 394using the 395.Fl p 396option of 397.Nm . 398.Sh TTL DETAILS 399The 400.Tn TTL 401value of an IP packet represents the maximum number of IP routers 402that the packet can go through before being thrown away. 403In current practice you can expect each router in the Internet to decrement 404the 405.Tn TTL 406field by exactly one. 407.Pp 408The 409.Tn TCP/IP 410specification recommends setting the 411.Tn TTL 412field for 413.Tn IP 414packets to 64, but many systems use smaller values 415.No ( Bx 4.3 416uses 30, 417.Bx 4.2 418used 15). 419.Pp 420The maximum possible value of this field is 255, and most 421.Ux 422systems set 423the 424.Tn TTL 425field of 426.Tn ICMP ECHO_REQUEST 427packets to 255. 428This is why you will find you can 429.Dq ping 430some hosts, but not reach them with 431.Xr telnet 1 432or 433.Xr ftp 1 . 434.Pp 435In normal operation 436.Nm 437prints the ttl value from the packet it receives. 438When a remote system receives a ping packet, it can do one of three things 439with the 440.Tn TTL 441field in its response: 442.Bl -bullet 443.It 444Not change it; this is what 445.Bx 446systems did before the 447.Bx 4.3 tahoe 448release. 449In this case the 450.Tn TTL 451value in the received packet will be 255 minus the 452number of routers in the round-trip path. 453.It 454Set it to 255; this is what current 455.Bx 456systems do. 457In this case the 458.Tn TTL 459value in the received packet will be 255 minus the 460number of routers in the path 461.Em from 462the remote system 463.Em to 464the 465.Nm Ns Em ing 466host. 467.It 468Set it to some other value. 469Some machines use the same value for 470.Tn ICMP 471packets that they use for 472.Tn TCP 473packets, for example either 30 or 60. 474Others may use completely wild values. 475.El 476.Sh RETURN VALUES 477The 478.Nm 479utility returns an exit status of zero if at least one response was 480heard from the specified 481.Ar host ; 482a status of two if the transmission was successful but no responses 483were received; or another value 484(from 485.In sysexits.h ) 486if an error occurred. 487.Sh SEE ALSO 488.Xr netstat 1 , 489.Xr ifconfig 8 , 490.Xr routed 8 , 491.Xr traceroute 8 492.Sh HISTORY 493The 494.Nm 495utility appeared in 496.Bx 4.3 . 497.Sh AUTHORS 498The original 499.Nm 500utility was written by 501.An Mike Muuss 502while at the US Army Ballistics 503Research Laboratory. 504.Sh BUGS 505Many Hosts and Gateways ignore the 506.Tn RECORD_ROUTE 507option. 508.Pp 509The maximum IP header length is too small for options like 510.Tn RECORD_ROUTE 511to be completely useful. 512.No There Ap s 513not much that can be done about this, however. 514.Pp 515Flood pinging is not recommended in general, and flood pinging the 516broadcast address should only be done under very controlled conditions. 517.Pp 518The 519.Fl v 520option is not worth much on busy hosts. 521