ping(8) System Manager's Manual ping(8)
NAME
ping - Sends ICMP ECHO_REQUEST packets to network hosts
SYNOPSIS
/usr/sbin/ping [-dfnqruvLR] [-b num] [-c count] [-i wait] [-l preload] [-p pattern] [-s packetsize] [-t number] [-I interface]
[-G[!]@addr1@addr2...] [-V version] host
FLAGS
Specifies the size of the receive buffer. You can use this when specifying very large packet sizes with the -s flag. By default, the size
of the receive buffer is set to 48K or to the size specified by the -s flag, whichever is greater. The -b flag overrides the default.
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). Specifies the source route for
packets to travel to the destination host. The route consists of one or more node names or addresses. Use the ampersand character (@) to
separate multiple addresses. You can specify up to 10 addresses.
The exclamation mark (!) indicates that this is a strict source route; ping uses only the specified hosts for intermediate hops.
If any of the specified addresses is a hostname, a lookup is performed and the protocol common to all addresses is used. If there
is no common protocol (for example, one host has only IPv4 address and one host has only IPv6 address), an error is printed. If all
hosts have both IPv4 and IPv6 addresses, IPv6 is used. You can override this option with the -V option. 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.
Sends packets through interface instead of using the interface specified in the routing tables for the host. Displays every 100th
reply only and displays a message indicating lost packets.
A packet loss rate of just 1% is enough to seriously impact UDP-based protocols like NFS. This option enables you to measure loss
rates and to determine how bursty they are. All lost messages are reported with the following message: Lost sequence number(s) num-
ber The number value is a single number or a range or numbers. 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 net-
work 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. Nothing is displayed except the summary lines at start-up time and
when finished. [ICMP over IPv4 only] 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. Sets the timeout period (in seconds) for ping to wait before terminating. The default timeout period is 10 seconds. This
option is only useful with -c 1 option. Displays the time in microseconds (three decimal places). In order to ensure this
microsecond precision, the NTP_TIME and MICRO_TIME kernel options 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.
Specifies verbose output. ICMP packets other than ECHO_RESPONSE that are received are listed. Specifies the Internet Protocol (IP)
version number to enable the resolver to return the correct address. If you are issuing a ping command to a host name (not IP
address) that has both IPv4 and IPv6 addresses, by default the command is issued using the IPv6 address. Use the -V4 option if you
want to use the IPv4 address.
DESCRIPTION
The ping command uses the ICMP (Internet Control Message Protocol) protocol'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 arbitrary number of pad bytes used to fill out the packet.
The operating system supports both ICMPv4 and ICMPv6.
When using ping for fault isolation, it should first be run on the local 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 summary 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.
ICMPv4 Packet Details
An IPv4 header without options is 20 bytes. An ICMPv4 ECHO_REQUEST packet contains an additional 8 bytes worth of ICMPv4 header followed
by an arbitrary 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 IPv4 packet of type ICMP ECHO_REPLY will always be 8 bytes more than the requested data
space (the ICMPv4 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
levels of duplicates may not always be cause for alarm.
Damaged packets are obviously serious cause for alarm and often indicate 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 depending on the data contained in the data portion. Unfortunately, data-
dependent problems have been known to sneak into networks and remain undetected for long periods of time. In many cases the particular
pattern that will have problems is something that does not have sufficient transitions, such as all 1s (ones) or all 0s (zeros), or a pat-
tern right at the edge, such as almost all 0s (zeros). It is not necessarily enough to specify a data pattern of all 0s (zeros) (for exam-
ple) 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
manage 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.
IPv4 TTL Details
The TTL value of an IPv4 packet represents the maximum number of IPv4 routers that the packet can go through before being thrown away. In
current practice you can expect each router in the Internet to decrement 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 compatible 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 receives. 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 ICMPv4 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)
RFC 792, Internet Control Message Protocol, Postel, J.
RFC 2463, Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification, Conta, A., and Deering, S.
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ping(8)