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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: src/sbin/ping/ping.8,v 1.25.2.11 2003/02/23 21:03:24 trhodes Exp $ 34.\" $DragonFly: src/sbin/ping/ping.8,v 1.4 2006/05/26 19:39:38 swildner Exp $ 35.\" 36.Dd September 25, 2001 37.Dt PING 8 38.Os 39.Sh NAME 40.Nm ping 41.Nd send 42.Tn ICMP ECHO_REQUEST 43packets to network hosts 44.Sh SYNOPSIS 45.Nm 46.Op Fl AQRadfnqrv 47.Op Fl c Ar count 48.Op Fl i Ar wait 49.Op Fl l Ar preload 50.Op Fl m Ar ttl 51.Op Fl p Ar pattern 52.Op Fl P Ar policy 53.Op Fl s Ar packetsize 54.Op Fl S Ar src_addr 55.Op Fl t Ar timeout 56.Bo 57.Ar host | 58.Op Fl L 59.Op Fl I Ar interface 60.Op Fl T Ar ttl 61.Ar mcast-group 62.Bc 63.Sh DESCRIPTION 64.Nm Ping 65uses 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. 82The options are as follows: 83.Bl -tag -width indent 84.It Fl A 85Audible. 86Output a bell 87.Tn ( ASCII 880x07) 89character when no packet is received before the next packet 90is transmitted. 91To cater for round-trip times that are longer than the interval 92between transmissions, further missing packets cause a bell only 93if the maximum number of unreceived packets has increased. 94.It Fl a 95Audible. 96Include a bell 97.Tn ( ASCII 980x07) 99character in the output when any packet is received. 100This option is ignored 101if other format options are present. 102.It Fl c Ar count 103Stop after sending 104(and receiving) 105.Ar count 106.Tn ECHO_RESPONSE 107packets. 108If this option is not specified, 109.Nm 110will operate until interrupted. 111.It Fl d 112Set the 113.Dv SO_DEBUG 114option on the socket being used. 115.It Fl f 116Flood ping. 117Outputs packets as fast as they come back or one hundred times per second, 118whichever is more. 119For every 120.Tn ECHO_REQUEST 121sent a period 122.Dq .\& 123is printed, while for every 124.Tn ECHO_REPLY 125received a backspace is printed. 126This provides a rapid display of how many packets are being dropped. 127Only the super-user may use this option. 128.Bf -emphasis 129This can be very hard on a network and should be used with caution. 130.Ef 131.It Fl i Ar wait 132Wait 133.Ar wait 134seconds 135.Em between sending each packet . 136The default is to wait for one second between each packet. 137The wait time may be fractional, but only the super-user may specify 138values less than 1 second. 139This option is incompatible with the 140.Fl f 141option. 142.It Fl I Ar interface 143Source multicast packets with the given interface address. 144This flag only applies if the ping destination is a multicast address. 145.It Fl l Ar preload 146If 147.Ar preload 148is specified, 149.Nm 150sends that many packets as fast as possible before falling into its normal 151mode of behavior. 152Only the super-user may use this option. 153.It Fl m Ar ttl 154Set the IP Time To Live for outgoing packets. 155If not specified, the kernel uses the value of the 156.Va net.inet.ip.ttl 157MIB variable. 158.It Fl L 159Suppress loopback of multicast packets. 160This flag only applies if the ping destination is a multicast address. 161.It Fl n 162Numeric output only. 163No attempt will be made to lookup symbolic names for host addresses. 164.It Fl p Ar pattern 165You may specify up to 16 166.Dq pad 167bytes to fill out the packet you send. 168This is useful for diagnosing data-dependent problems in a network. 169For example, 170.Dq Li \-p ff 171will cause the sent packet to be filled with all 172ones. 173.It Fl P Ar policy 174.Ar policy 175specifies IPsec policy for the ping session. 176For details please refer to 177.Xr ipsec 4 178and 179.Xr ipsec_set_policy 3 . 180.It Fl Q 181Somewhat quiet output. 182.No Don Ap t 183display ICMP error messages that are in response to our query messages. 184Originally, the 185.Fl v 186flag was required to display such errors, but 187.Fl v 188displays all ICMP error messages. 189On a busy machine, this output can 190be overbearing. 191Without the 192.Fl Q 193flag, 194.Nm 195prints out any ICMP error messages caused by its own ECHO_REQUEST 196messages. 197.It Fl q 198Quiet output. 199Nothing is displayed except the summary lines at startup time and 200when finished. 201.It Fl R 202Record route. 203Includes the 204.Tn RECORD_ROUTE 205option in the 206.Tn ECHO_REQUEST 207packet and displays 208the route buffer on returned packets. 209Note that the IP header is only large enough for nine such routes; 210the 211.Xr traceroute 8 212command is usually better at determining the route packets take to a 213particular destination. 214If more routes come back than should, such as due to an illegal spoofed 215packet, ping will print the route list and then truncate it at the correct 216spot. 217Many hosts ignore or discard the 218.Tn RECORD_ROUTE 219option. 220.It Fl r 221Bypass the normal routing tables and send directly to a host on an attached 222network. 223If the host is not on a directly-attached network, an error is returned. 224This option can be used to ping a local host through an interface 225that has no route through it 226(e.g., after the interface was dropped by 227.Xr routed 8 ) . 228.It Fl s Ar packetsize 229Specify the number of data bytes to be sent. 230The default is 56, which translates into 64 231.Tn ICMP 232data bytes when combined 233with the 8 bytes of 234.Tn ICMP 235header data. 236Only the super-user may use this option. 237.It Fl S Ar src_addr 238Use the following IP address as the source address in outgoing packets. 239On hosts with more than one IP address, this option can be used to 240force the source address to be something other than the IP address 241of the interface the probe packet is sent on. 242If the IP address is not one of this machine's interface addresses, 243an error is returned and nothing is sent. 244.It Fl t Ar timeout 245Specify a timeout, in seconds, before ping exits regardless of how 246many packets have been received. 247.It Fl T Ar ttl 248Set the IP Time To Live for multicasted packets. 249This flag only applies if the ping destination is a multicast address. 250.It Fl v 251Verbose output. 252.Tn ICMP 253packets other than 254.Tn ECHO_RESPONSE 255that are received are listed. 256.El 257.Pp 258When using 259.Nm 260for fault isolation, it should first be run on the local host, to verify 261that the local network interface is up and running. 262Then, hosts and gateways further and further away should be 263.Dq pinged . 264Round-trip times and packet loss statistics are computed. 265If duplicate packets are received, they are not included in the packet 266loss calculation, although the round trip time of these packets is used 267in calculating the round-trip time statistics. 268When the specified number of packets have been sent 269(and received) 270or if the program is terminated with a 271.Dv SIGINT , 272a brief summary is displayed, showing the number of packets sent and 273received, and the minimum, mean, maximum, and standard deviation of 274the round-trip times. 275.Pp 276If 277.Nm 278receives a 279.Dv SIGINFO 280(see the 281.Cm status 282argument for 283.Xr stty 1 ) 284signal, the current number of packets sent and received, and the 285minimum, mean, and maximum of the round-trip times will be written to 286the standard error output. 287.Pp 288This program is intended for use in network testing, measurement and 289management. 290Because of the load it can impose on the network, it is unwise to use 291.Nm 292during normal operations or from automated scripts. 293.Sh ICMP PACKET DETAILS 294An IP header without options is 20 bytes. 295An 296.Tn ICMP 297.Tn ECHO_REQUEST 298packet contains an additional 8 bytes worth of 299.Tn ICMP 300header followed by an arbitrary amount of data. 301When a 302.Ar packetsize 303is given, this indicated the size of this extra piece of data 304(the default is 56). 305Thus the amount of data received inside of an IP packet of type 306.Tn ICMP 307.Tn ECHO_REPLY 308will always be 8 bytes more than the requested data space 309(the 310.Tn ICMP 311header). 312.Pp 313If the data space is at least eight bytes large, 314.Nm 315uses the first eight bytes of this space to include a timestamp which 316it uses in the computation of round trip times. 317If less than eight bytes of pad are specified, no round trip times are 318given. 319.Sh DUPLICATE AND DAMAGED PACKETS 320.Nm Ping 321will 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 DIAGNOSTICS 445The 446.Nm 447command 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.In 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 463command appeared in 464.Bx 4.3 . 465.Sh AUTHORS 466The original 467.Nm 468command 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