1.\" Copyright (c) 1985, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)ping.8 8.2 (Berkeley) 12/11/93 7.\" 8.Dd 9.Dt PING 8 10.Os BSD 4.3 11.Sh NAME 12.Nm ping 13.Nd send 14.Tn ICMP ECHO_REQUEST 15packets to network hosts 16.Sh SYNOPSIS 17.Nm ping 18.Op Fl dfnqrvR 19.Op Fl c Ar count 20.Op Fl i Ar wait 21.Op Fl l Ar preload 22.Op Fl p Ar pattern 23.Op Fl s Ar packetsize 24.Sh DESCRIPTION 25.Nm Ping 26uses the 27.Tn ICMP 28protocol's mandatory 29.Tn ECHO_REQUEST 30datagram to elicit an 31.Tn ICMP ECHO_RESPONSE 32from a host or gateway. 33.Tn ECHO_REQUEST 34datagrams (``pings'') have an IP and 35.Tn ICMP 36header, 37followed by a 38.Dq struct timeval 39and then an arbitrary number of ``pad'' bytes used to fill out the 40packet. 41The options are as follows: 42.Bl -tag -width Ds 43.It Fl c Ar count 44Stop after sending (and receiving) 45.Ar count 46.Tn ECHO_RESPONSE 47packets. 48.It Fl d 49Set the 50.Dv SO_DEBUG 51option on the socket being used. 52.It Fl f 53Flood ping. 54Outputs packets as fast as they come back or one hundred times per second, 55whichever is more. 56For every 57.Tn ECHO_REQUEST 58sent a period ``.'' is printed, while for every 59.Tn ECHO_REPLY 60received a backspace is printed. 61This provides a rapid display of how many packets are being dropped. 62Only the super-user may use this option. 63.Bf -emphasis 64This can be very hard on a network and should be used with caution. 65.Ef 66.It Fl i Ar wait 67Wait 68.Ar wait 69seconds 70.Em between sending each packet . 71The default is to wait for one second between each packet. 72This option is incompatible with the 73.Fl f 74option. 75.It Fl l Ar preload 76If 77.Ar preload 78is specified, 79.Nm ping 80sends that many packets as fast as possible before falling into its normal 81mode of behavior. 82.It Fl n 83Numeric output only. 84No attempt will be made to lookup symbolic names for host addresses. 85.It Fl p Ar pattern 86You may specify up to 16 ``pad'' bytes to fill out the packet you send. 87This is useful for diagnosing data-dependent problems in a network. 88For example, 89.Dq Li \-p ff 90will cause the sent packet to be filled with all 91ones. 92.It Fl q 93Quiet output. 94Nothing is displayed except the summary lines at startup time and 95when finished. 96.It Fl R 97Record route. 98Includes the 99.Tn RECORD_ROUTE 100option in the 101.Tn ECHO_REQUEST 102packet and displays 103the route buffer on returned packets. 104Note that the IP header is only large enough for nine such routes. 105Many hosts ignore or discard this option. 106.It Fl r 107Bypass the normal routing tables and send directly to a host on an attached 108network. 109If the host is not on a directly-attached network, an error is returned. 110This option can be used to ping a local host through an interface 111that has no route through it (e.g., after the interface was dropped by 112.Xr routed 8 ) . 113.It Fl s Ar packetsize 114Specifies the number of data bytes to be sent. 115The default is 56, which translates into 64 116.Tn ICMP 117data bytes when combined 118with the 8 bytes of 119.Tn ICMP 120header data. 121.It Fl v 122Verbose output. 123.Tn ICMP 124packets other than 125.Tn ECHO_RESPONSE 126that are received are listed. 127.El 128.Pp 129When using 130.Nm ping 131for fault isolation, it should first be run on the local host, to verify 132that the local network interface is up and running. 133Then, hosts and gateways further and further away should be ``pinged''. 134Round-trip times and packet loss statistics are computed. 135If duplicate packets are received, they are not included in the packet 136loss calculation, although the round trip time of these packets is used 137in calculating the minimum/average/maximum round-trip time numbers. 138When the specified number of packets have been sent (and received) or 139if the program is terminated with a 140.Dv SIGINT , 141a brief summary is displayed. 142.Pp 143This program is intended for use in network testing, measurement and 144management. 145Because of the load it can impose on the network, it is unwise to use 146.Nm ping 147during normal operations or from automated scripts. 148.Sh ICMP PACKET DETAILS 149An IP header without options is 20 bytes. 150An 151.Tn ICMP 152.Tn ECHO_REQUEST 153packet contains an additional 8 bytes worth 154of 155.Tn ICMP 156header followed by an arbitrary amount of data. 157When a 158.Ar packetsize 159is given, this indicated the size of this extra piece of data (the 160default is 56). 161Thus the amount of data received inside of an IP packet of type 162.Tn ICMP 163.Tn ECHO_REPLY 164will always be 8 bytes more than the requested data space 165(the 166.Tn ICMP 167header). 168.Pp 169If the data space is at least eight bytes large, 170.Nm ping 171uses the first eight bytes of this space to include a timestamp which 172it uses in the computation of round trip times. 173If less than eight bytes of pad are specified, no round trip times are 174given. 175.Sh DUPLICATE AND DAMAGED PACKETS 176.Nm Ping 177will report duplicate and damaged packets. 178Duplicate packets should never occur, and seem to be caused by 179inappropriate link-level retransmissions. 180Duplicates may occur in many situations and are rarely (if ever) a 181good sign, although the presence of low levels of duplicates may not 182always be cause for alarm. 183.Pp 184Damaged packets are obviously serious cause for alarm and often 185indicate broken hardware somewhere in the 186.Nm ping 187packet's path (in the network or in the hosts). 188.Sh TRYING DIFFERENT DATA PATTERNS 189The (inter)network layer should never treat packets differently depending 190on the data contained in the data portion. 191Unfortunately, data-dependent problems have been known to sneak into 192networks and remain undetected for long periods of time. 193In many cases the particular pattern that will have problems is something 194that doesn't have sufficient ``transitions'', such as all ones or all 195zeros, or a pattern right at the edge, such as almost all zeros. 196It isn't necessarily enough to specify a data pattern of all zeros (for 197example) on the command line because the pattern that is of interest is 198at the data link level, and the relationship between what you type and 199what the controllers transmit can be complicated. 200.Pp 201This means that if you have a data-dependent problem you will probably 202have to do a lot of testing to find it. 203If you are lucky, you may manage to find a file that either can't be sent 204across your network or that takes much longer to transfer than other 205similar length files. 206You can then examine this file for repeated patterns that you can test 207using the 208.Fl p 209option of 210.Nm ping . 211.Sh TTL DETAILS 212The 213.Tn TTL 214value of an IP packet represents the maximum number of IP routers 215that the packet can go through before being thrown away. 216In current practice you can expect each router in the Internet to decrement 217the 218.Tn TTL 219field by exactly one. 220.Pp 221The 222.Tn TCP/IP 223specification states that the 224.Tn TTL 225field for 226.Tn TCP 227packets should 228be set to 60, but many systems use smaller values (4.3 229.Tn BSD 230uses 30, 4.2 used 23115). 232.Pp 233The maximum possible value of this field is 255, and most Unix systems set 234the 235.Tn TTL 236field of 237.Tn ICMP ECHO_REQUEST 238packets to 255. 239This is why you will find you can ``ping'' some hosts, but not reach them 240with 241.Xr telnet 1 242or 243.Xr ftp 1 . 244.Pp 245In normal operation ping prints the ttl value from the packet it receives. 246When a remote system receives a ping packet, it can do one of three things 247with the 248.Tn TTL 249field in its response: 250.Bl -bullet 251.It 252Not change it; this is what Berkeley Unix systems did before the 253.Bx 4.3 tahoe 254release. 255In this case the 256.Tn TTL 257value in the received packet will be 255 minus the 258number of routers in the round-trip path. 259.It 260Set it to 255; this is what current Berkeley Unix systems do. 261In this case the 262.Tn TTL 263value in the received packet will be 255 minus the 264number of routers in the path 265.Xr from 266the remote system 267.Em to 268the 269.Nm ping Ns Em ing 270host. 271.It 272Set it to some other value. 273Some machines use the same value for 274.Tn ICMP 275packets that they use for 276.Tn TCP 277packets, for example either 30 or 60. 278Others may use completely wild values. 279.El 280.Sh BUGS 281Many Hosts and Gateways ignore the 282.Tn RECORD_ROUTE 283option. 284.Pp 285The maximum IP header length is too small for options like 286.Tn RECORD_ROUTE 287to 288be completely useful. 289There's not much that that can be done about this, however. 290.Pp 291Flood pinging is not recommended in general, and flood pinging the 292broadcast address should only be done under very controlled conditions. 293.Sh SEE ALSO 294.Xr netstat 1 , 295.Xr ifconfig 8 , 296.Xr routed 8 297.Sh HISTORY 298The 299.Nm 300command appeared in 301.Bx 4.3 . 302