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ping(8) System Manager's Manual ping(8) NAME ping - Sends ICMP ECHO_REQUEST packets to network hosts SYNOPSIS /usr/sbin/ping [-dfnqruvR] [-c count] [-i wait] [-l preload] [-p pat- tern] [-s packetsize] host FLAGS Stops after sending (and receiving) count ECHO_RESPONSE packets. Set the SO_DEBUG option on the socket being used. Floods ping. Outputs packets as fast as they come back or 100 times per second, whichever is more. For every ECHO_REQUEST sent, a . (dot) is printed, while for every ECHO_REPLY received a backspace is used. This provides a rapid display of how many packets are being dropped. Only the superuser may use this option. This can be very hard on a network and should be used with caution (see Cautions). Waits wait seconds between sending each packet. The default is to wait for 1 second between each packet. This option is incompatible with the -f option. If preload is specified, ping sends that many packets as fast as possible before falling into its normal mode of behavior. Only the superuser may use this option. This can be very hard on a network and should be used with caution (see Cautions). Numeric output only. No attempt will be made to look up symbolic names for host addresses. This occurs only when displaying ICMP packets other than ECHO_RESPONSE. You may specify up to 16 pad bytes to fill out the packet you send. This is useful for diagnosing data-dependent problems in a network. For example, -p ff will cause the sent packet to be filled with all 1s (ones). Quiets output. Noth- ing is displayed except the summary lines at start-up time and when finished. Records route. Includes the RECORD_ROUTE option in the ECHO_REQUEST packet and displays the route buffer on returned packets. Note that the IP header is only large enough for nine such routes. Many hosts ignore or discard this option. Bypasses the normal routing tables and directly sends to a host on an attached network. If the host is not on a directly attached network, an error is returned. This option can be used to send ping to a local host through an interface that has no route through it (for example, after the interface was dropped by routed). Specifies the number of data bytes to be sent. The default is 56, which translates into 64 ICMP data bytes when combined with the 8 bytes of ICMP header data. Dis- plays the time in microseconds (three decimal places). In order to en- sure this microsecond precision, the NTP_TIME and MICRO_TIME kernel op- tions must be on. By default NTP_TIME and MICRO_TIME kernel options are off. If these kernel options are off and this flag is used, the time is displayed to three decimal places, but in milliseconds. Speci- fies verbose output. ICMP packets other than ECHO_RESPONSE that are received are listed. DESCRIPTION The ping command uses the ICMP (Internet Control Message Protocol) pro- tocol's mandatory ECHO_REQUEST datagram to elicit an ICMP ECHO_RESPONSE from the specified host or gateway host, where host is a network name or IP address. ECHO_REQUEST datagrams (pings) have an IP (Internet Protocol) and ICMP header, followed by a struct timeval and then an ar- bitrary number of pad bytes used to fill out the packet. When using ping for fault isolation, it should first be run on the lo- cal host to verify that the local network interface is up and running. Then, hosts and gateways further and further away should be sent the ping command. Round-trip times and packet loss statistics are com- puted. If duplicate packets are received, they are not included in the packet loss calculations, although the round-trip time of these packets is used in calculating the minimum, average, and maximum round-trip time numbers. When the specified number of packets have been sent (and received) or if the program is terminated with a SIGINT, a brief sum- mary is displayed. This program is intended for use in network testing, measurement, and management. Because of the load it can impose on the network, it is unwise to use ping during normal operations or from automated scripts. ICMP Packet Details An IP header without options is 20 bytes. An ICMP ECHO_REQUEST packet contains an additional 8 bytes worth of ICMP header followed by an ar- bitrary amount of data. When a packetsize is given, this indicates the size of this extra piece of data (the default is 56). Thus, the amount of data received inside of an IP packet of type ICMP ECHO_REPLY will always be 8 bytes more than the requested data space (the ICMP header). If the data space is at least 8 bytes large, ping uses the first 8 bytes of this space to include a timestamp, which it uses in the compu- tation of round-trip times. If less than 8 bytes of pad are specified, no round-trip times are given. Duplicate and Damaged Packets The ping command will report duplicate and damaged packets. Duplicate packets should never occur, and seem to be caused by inappropriate link-level retransmissions. Duplicates may occur in many situations and are rarely (if ever) a good sign, although the presence of low lev- els of duplicates may not always be cause for alarm. Damaged packets are obviously serious cause for alarm and often indi- cate broken hardware somewhere in the ping packet's path (in the net- work or in the hosts). Trying Different Data Patterns The (inter)network layer should never treat packets differently depend- ing on the data contained in the data portion. Unfortunately, data-de- pendent problems have been known to sneak into networks and remain un- detected for long periods of time. In many cases the particular pat- tern that will have problems is something that does not have sufficient transitions, such as all 1s (ones) or all 0s (zeros), or a pattern right at the edge, such as almost all 0s (zeros). It is not necessar- ily enough to specify a data pattern of all 0s (zeros) (for example) on the command line because the pattern that is of interest is at the data-link level, and the relationship between what you enter and what the controllers transmit can be complicated. This means that if you have a data-dependent problem you will probably have to do a lot of testing to find it. If you are lucky, you may man- age to find a file that either cannot be sent across your network or that takes much longer to transfer than other similar length files. You can then examine this file for repeated patterns that you can test using the -p option of ping. TTL Details The TTL value of an IP packet represents the maximum number of IP routers that the packet can go through before being thrown away. In current practice you can expect each router in the Internet to decre- ment the TTL field by exactly 1 (one). The TCP/IP specification states that the TTL field for TCP packets should be set to 60, but many systems use smaller values (4.3BSD uses 30, 4.2BSD used 15). The maximum possible value of this field is 255, and most UNIX compati- ble systems set the TTL field of ICMP ECHO_REQUEST packets to 255. This is why you will find you can use the ping command on some hosts, but not reach them with telnet or ftp. In normal operation, ping prints the TTL value from the packet it re- ceives. When a remote system receives a ping packet, it can do one of three things with the TTL field in its response: Not change it; this is what Berkeley UNIX compatible systems did before the 4.3BSD release. In this case, the TTL value in the received packet will be 255 minus the number of routers in the round-trip path. Set it to 255; this is what current Berkeley UNIX compatible systems do. In this case, the TTL value in the received packet will be 255 minus the number of routers in the path from the remote system to the host that received the ping command. Set it to some other value. Some machines use the same value for ICMP packets that they use for TCP packets; for example, either 30 or 60. Others may use completely wild values. CAUTIONS Many hosts and gateways ignore the RECORD_ROUTE option. Flooding and preloading the ping command is not recommended in general, and flooding ping on the broadcast address should only be done under very controlled conditions. FILES Specifies the command path RELATED INFORMATION Commands: netstat(1), ifconfig(8) Daemons: gated(8), routed(8) delim off ping(8)