ping —
send ICMP
ECHO_REQUEST packets to network hosts
ping |
[option ...]
host ...
|
ping uses the ICMP protocol's mandatory
ECHO_REQUEST datagram to elicit an ICMP ECHO_RESPONSE from a host or gateway.
ECHO_REQUEST datagrams ("pings") have an IP and ICMP header,
followed by a “struct timeval” and then an arbitrary number of
"pad" bytes used to fill out the packet.
- --address
- Send ICMP_ADDRESS packets (root only).
- --mask
- Same as --address.
- --echo
- Send ICMP_ECHO packets (default).
- --timestamp
- Send ICMP_TIMESTAMP packets.
-
-t,
--type
type
- Send type packets.
-
-c,
--count
count
- Stop after sending (and receiving)
count ECHO_RESPONSE packets.
-
-d,
--debug
- Set the
SO_DEBUG
option
on the socket being used.
-
-f,
--flood
- Flood ping. Outputs packets as fast as they come back or
one hundred times per second, whichever is more. For every ECHO_REQUEST
sent a period "." is printed, while for every ECHO_REPLY
received a backspace is printed. This provides a rapid display of how many
packets are being dropped. Only the super-user may use this option.
-
-i,
--interval
wait
- Wait wait seconds
between sending each packet. The default is
to wait for one second between each packet. This option is incompatible
with the -f option.
-
-l,
--preload
preload
- If preload is specified,
ping sends that many packets as fast as
possible before falling into its normal mode of behavior.
-
-n,
--numeric
- Numeric output only. No attempt will be made to lookup
symbolic names for host addresses.
-
-p,
--pattern
pattern
- 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 ones.
-
-q,
--quiet
- Quiet output. Nothing is displayed except the summary lines
at startup time and when finished.
-
-R,
--route
- Record 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.
-
-r,
--ignore-routing
- Bypass the normal routing tables and send directly 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 ping a local
host through an interface that has no route through it (e.g., after the
interface was dropped by routed(8)).
-
-s,
--size
packetsize
- 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.
-
-v,
--verbose
- Verbose output. ICMP packets other than ECHO_RESPONSE that
are received are listed.
-
--ttl
N
- Set N as the packet
time-to-live.
-
-T,
--tos num
- Set num as the packet type
of service (TOS).
-
-w,
--timeout
N
- Stop after N seconds of
sending packets.
-
-W,
--linger
N
- Number of seconds to wait for response.
-
--ip-timestamp
flag
- IP timestamp of type flag,
which is one of "tsonly" and "tsaddr".
-
-?,
--help
- Display a help list.
- --usage
- Display a short usage message.
-
-V,
--version
- Print the program version.
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
"pinged". Round-trip times and packet loss statistics are computed.
If duplicate packets are received, they are not included in the packet loss
calculation, although the round trip time of these packets is used in
calculating the minimum/average/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.
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 arbitrary amount of
data. When a
packetsize is given, this
indicated 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 eight bytes large,
ping uses the first eight bytes of this space to
include a timestamp which it uses in the computation of round trip times. If
less than eight bytes of pad are specified, no round trip times are given.
ping 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 network or in the hosts).
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 doesn't have sufficient "transitions", such as all
ones or all zeros, or a pattern right at the edge, such as almost all zeros.
It isn't necessarily enough to specify a data pattern of all 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 type 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 can't 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.
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 decrement the TTL field by exactly
one.
The TCP/IP specification states that the TTL field for TCP packets should be set
to 60, but many systems use smaller values (4.3 BSD uses 30, 4.2 used 15).
The maximum possible value of this field is 255, and most Unix systems set the
TTL field of ICMP ECHO_REQUEST packets to 255. This is why you will find you
can "ping" some hosts, but not reach them with
telnet(1) or
ftp(1).
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 systems did
before the 4.3BSD-Tahoe 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
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
pinging
host.
- 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.
Many Hosts and Gateways ignore the RECORD_ROUTE option.
The maximum IP header length is too small for options like RECORD_ROUTE to be
completely useful. There's not much that that can be done about this, however.
Flood pinging is not recommended in general, and flood pinging the broadcast
address should only be done under very controlled conditions.
netstat(1),
ifconfig(1),
routed(8)
The
ping command appeared in
4.3BSD.