1.\" Copyright (c) 1985, 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)ping.8 6.7 (Berkeley) 03/16/91 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: 42Other options are: 43.Bl -tag -width Ds 44.It Fl c Ar count 45Stop after sending (and receiving) 46.Ar count 47.Tn ECHO_RESPONSE 48packets. 49.It Fl d 50Set the 51.Dv SO_DEBUG 52option on the socket being used. 53.It Fl f 54Flood ping. 55Outputs packets as fast as they come back or one hundred times per second, 56whichever is more. 57For every 58.Tn ECHO_REQUEST 59sent a period ``.'' is printed, while for ever 60.Tn ECHO_REPLY 61received a backspace is printed. 62This provides a rapid display of how many packets are being dropped. 63Only the super-user may use this option. 64.Bf -emphasis 65This can be very hard on a network and should be used with caution. 66.Ef 67.It Fl i Ar wait 68Wait 69.Ar wait 70seconds 71.Em between sending each packet . 72The default is to wait for one second between each packet. 73This option is incompatible with the 74.Fl f 75option. 76.It Fl l Ar preload 77If 78.Ar preload 79is specified, 80.Nm ping 81sends that many packets as fast as possible before falling into its normal 82mode of behavior. 83.It Fl n 84Numeric output only. 85No attempt will be made to lookup symbolic names for host addresses. 86.It Fl p Ar pattern 87You may specify up to 16 ``pad'' bytes to fill out the packet you send. 88This is useful for diagnosing data-dependent problems in a network. 89For example, 90.Dq Li \-p ff 91will cause the sent packet to be filled with all 92ones. 93.It Fl q 94Quiet output. 95Nothing is displayed except the summary lines at startup time and 96when finished. 97.It Fl R 98Record route. 99Includes the 100.Tn RECORD_ROUTE 101option in the 102.Tn ECHO_REQUEST 103packet and displays 104the route buffer on returned packets. 105Note that the IP header is only large enough for nine such routes. 106Many hosts ignore or discard this option. 107.It Fl r 108Bypass the normal routing tables and send directly to a host on an attached 109network. 110If the host is not on a directly-attached network, an error is returned. 111This option can be used to ping a local host through an interface 112that has no route through it (e.g., after the interface was dropped by 113.Xr routed 8 ) . 114.It Fl s Ar packetsize 115Specifies the number of data bytes to be sent. 116The default is 56, which translates into 64 117.Tn ICMP 118data bytes when combined 119with the 8 bytes of 120.Tn ICMP 121header data. 122.It Fl v 123Verbose output. 124.Tn ICMP 125packets other than 126.Tn ECHO_RESPONSE 127that are received are listed. 128.El 129.Pp 130When using 131.Nm ping 132for fault isolation, it should first be run on the local host, to verify 133that the local network interface is up and running. 134Then, hosts and gateways further and further away should be ``pinged''. 135Round-trip times and packet loss statistics are computed. 136If duplicate packets are received, they are not included in the packet 137loss calculation, although the round trip time of these packets is used 138in calculating the minimum/average/maximum round-trip time numbers. 139When the specified number of packets have been sent (and received) or 140if the program is terminated with a 141.Dv SIGINT , 142a brief summary is displayed. 143.Pp 144This program is intended for use in network testing, measurement and 145management. 146Because of the load it can impose on the network, it is unwise to use 147.Nm ping 148during normal operations or from automated scripts. 149.Sh ICMP PACKET DETAILS 150An IP header without options is 20 bytes. 151An 152.Tn ICMP 153.Tn ECHO_REQUEST 154packet contains an additional 8 bytes worth 155of 156.Tn ICMP 157header followed by an arbitrary amount of data. 158When a 159.Ar packetsize 160is given, this indicated the size of this extra piece of data (the 161default is 56). 162Thus the amount of data received inside of an IP packet of type 163.Tn ICMP 164.Tn ECHO_REPLY 165will always be 8 bytes more than the requested data space 166(the 167.Tn ICMP 168header). 169.Pp 170If the data space is at least eight bytes large, 171.Nm ping 172uses the first eight bytes of this space to include a timestamp which 173it uses in the computation of round trip times. 174If less than eight bytes of pad are specified, no round trip times are 175given. 176.Sh DUPLICATE AND DAMAGED PACKETS 177.Nm Ping 178will report duplicate and damaged packets. 179Duplicate packets should never occur, and seem to be caused by 180inappropriate link-level retransmissions. 181Duplicates may occur in many situations and are rarely (if ever) a 182good sign, although the presence of low levels of duplicates may not 183always be cause for alarm. 184.Pp 185Damaged packets are obviously serious cause for alarm and often 186indicate broken hardware somewhere in the 187.Nm ping 188packet's path (in the network or in the hosts). 189.Sh TRYING DIFFERENT DATA PATTERNS 190The (inter)network layer should never treat packets differently depending 191on the data contained in the data portion. 192Unfortunately, data-dependent problems have been known to sneak into 193networks and remain undetected for long periods of time. 194In many cases the particular pattern that will have problems is something 195that doesn't have sufficient ``transitions'', such as all ones or all 196zeros, or a pattern right at the edge, such as almost all zeros. 197It isn't necessarily enough to specify a data pattern of all zeros (for 198example) on the command line because the pattern that is of interest is 199at the data link level, and the relationship between what you type and 200what the controllers transmit can be complicated. 201.Pp 202This means that if you have a data-dependent problem you will probably 203have to do a lot of testing to find it. 204If you are lucky, you may manage to find a file that either can't be sent 205across your network or that takes much longer to transfer than other 206similar length files. 207You can then examine this file for repeated patterns that you can test 208using the 209.Fl p 210option of 211.Nm ping . 212.Sh TTL DETAILS 213The 214.Tn TTL 215value of an IP packet represents the maximum number of IP routers 216that the packet can go through before being thrown away. 217In current practice you can expect each router in the Internet to decrement 218the 219.Tn TTL 220field by exactly one. 221.Pp 222The 223.Tn TCP/IP 224specification states that the 225.Tn TTL 226field for 227.Tn TCP 228packets should 229be set to 60, but many systems use smaller values (4.3 230.Tn BSD 231uses 30, 4.2 used 23215). 233.Pp 234The maximum possible value of this field is 255, and most Unix systems set 235the 236.Tn TTL 237field of 238.Tn ICMP ECHO_REQUEST 239packets to 255. 240This is why you will find you can ``ping'' some hosts, but not reach them 241with 242.Xr telnet 1 243or 244.Xr ftp 1 . 245.Pp 246In normal operation ping prints the ttl value from the packet it receives. 247When a remote system receives a ping packet, it can do one of three things 248with the 249.Tn TTL 250field in its response: 251.Bl -bullet 252.It 253Not change it; this is what Berkeley Unix systems did before the 254.Bx 4.3 tahoe 255release. 256In this case the 257.Tn TTL 258value in the received packet will be 255 minus the 259number of routers in the round-trip path. 260.It 261Set it to 255; this is what current Berkeley Unix systems do. 262In this case the 263.Tn TTL 264value in the received packet will be 255 minus the 265number of routers in the path 266.Xr from 267the remote system 268.Em to 269the 270.Nm ping Ns Em ing 271host. 272.It 273Set it to some other value. 274Some machines use the same value for 275.Tn ICMP 276packets that they use for 277.Tn TCP 278packets, for example either 30 or 60. 279Others may use completely wild values. 280.El 281.Sh BUGS 282Many Hosts and Gateways ignore the 283.Tn RECORD_ROUTE 284option. 285.Pp 286The maximum IP header length is too small for options like 287.Tn RECORD_ROUTE 288to 289be completely useful. 290There's not much that that can be done about this, however. 291.Pp 292Flood pinging is not recommended in general, and flood pinging the 293broadcast address should only be done under very controlled conditions. 294.Sh SEE ALSO 295.Xr netstat 1 , 296.Xr ifconfig 8 , 297.Xr routed 8 298.Sh HISTORY 299The 300.Nm 301command appeared in 302.Bx 4.3 . 303