The
utility uses the
ICMPprotocol Ap 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.
The options are as follows:
-A
Audible.
Output a bell
( ASCII
0x07)
character when no packet is received before the next packet
is transmitted.
To cater for round-trip times that are longer than the interval
between transmissions, further missing packets cause a bell only
if the maximum number of unreceived packets has increased.
-a
Audible.
Include a bell
( ASCII
0x07)
character in the output when any packet is received.
This option is ignored
if other format options are present.
-c count
Stop after sending
(and receiving)
countECHO_RESPONSE
packets.
If this option is not specified,
will operate until interrupted.
If this option is specified in conjunction with ping sweeps,
each sweep will consist of
count
packets.
-D
Set the Don't Fragment bit.
-d
Set the
SO_DEBUG
option on the socket being used.
-f
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.
Bf -emphasis
This can be very hard on a network and should be used with caution.
Ef
-G sweepmaxsize
Specify the maximum size of
ICMP
payload when sending sweeping pings.
This option is required for ping sweeps.
-g sweepminsize
Specify the size of
ICMP
payload to start with when sending sweeping pings.
The default value is 0.
-h sweepincrsize
Specify the number of bytes to increment the size of
ICMP
payload after
each sweep when sending sweeping pings.
The default value is 1.
-I iface
Source multicast packets with the given interface address.
This flag only applies if the ping destination is a multicast address.
-i wait
Wait
wait
seconds
between sending each packet
The default is to wait for one second between each packet.
The wait time may be fractional, but only the super-user may specify
values less than 1 second.
This option is incompatible with the
-f
option.
-L
Suppress loopback of multicast packets.
This flag only applies if the ping destination is a multicast address.
-l preload
If
preload
is specified,
sends that many packets as fast as possible before falling into its normal
mode of behavior.
Only the super-user may use this option.
-M mask | time
Use
ICMP_MASKREQ
or
ICMP_TSTAMP
instead of
ICMP_ECHO
For
mask
print the netmask of the remote machine.
Set the
net.inet.icmp.maskrepl
MIB variable to enable
ICMP_MASKREPLY
For
time
print the origination, reception and transmission timestamps.
-m ttl
Set the IP Time To Live for outgoing packets.
If not specified, the kernel uses the value of the
net.inet.ip.ttl
MIB variable.
-n
Numeric output only.
No attempt will be made to lookup symbolic names for host addresses.
-o
Exit successfully after receiving one reply packet.
-P policy
policy
specifies IPsec policy for the ping session.
For details please refer to
ipsec(4)
and
ipsec_set_policy3.
-p 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
Somewhat quiet output.
Don Ap t
display ICMP error messages that are in response to our query messages.
Originally, the
-v
flag was required to display such errors, but
-v
displays all ICMP error messages.
On a busy machine, this output can be overbearing.
Without the
-Q
flag,
prints out any ICMP error messages caused by its own ECHO_REQUEST
messages.
-q
Quiet output.
Nothing is displayed except the summary lines at startup time and
when finished.
-R
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;
the
traceroute(8)
command is usually better at determining the route packets take to a
particular destination.
If more routes come back than should, such as due to an illegal spoofed
packet, ping will print the route list and then truncate it at the correct
spot.
Many hosts ignore or discard the
RECORD_ROUTE
option.
-r
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 src_addr
Use the following IP address as the source address in outgoing packets.
On hosts with more than one IP address, this option can be used to
force the source address to be something other than the IP address
of the interface the probe packet is sent on.
If the IP address
is not one of this machine's interface addresses, an error is
returned and nothing is sent.
-s packetsize
Specify 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.
Only the super-user may specify values more than default.
This option cannot be used with ping sweeps.
-T ttl
Set the IP Time To Live for multicasted packets.
This flag only applies if the ping destination is a multicast address.
-t timeout
Specify a timeout, in seconds, before ping exits regardless of how
many packets have been received.
-v
Verbose output.
ICMP
packets other than
ECHO_RESPONSE
that are received are listed.
-W waittime
Time in milliseconds to wait for a reply for each packet sent.
If a reply arrives later, the packet is not printed as replied, but
considered as replied when calculating statistics.
-z tos
Use the specified type of service.
When using
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 round-trip time statistics.
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, showing the number of packets sent and
received, and the minimum, mean, maximum, and standard deviation of
the round-trip times.
If
receives a
SIGINFO
(see the
status
argument for
stty(1))
signal, the current number of packets sent and received, and the
minimum, mean, and maximum of the round-trip times will be written to
the standard error output.
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
during normal operations or from automated scripts.
ICMP PACKET DETAILS
An IP header without options is 20 bytes.
An
ICMPECHO_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
ICMPECHO_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,
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.
DUPLICATE AND DAMAGED PACKETS
The
utility will report duplicate and damaged packets.
Duplicate packets should never occur when pinging a unicast address,
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.
Duplicates are expected when pinging a broadcast or multicast address,
since they are not really duplicates but replies from different hosts
to the same request.
Damaged packets are obviously serious cause for alarm and often
indicate broken hardware somewhere in the
packet's path (in the network 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 ones or all zeros, or a pattern right at the edge, such as
almost all zeros.
It is not
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
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
.
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 decrement
the
TTL
field by exactly one.
The
TCP/IP
specification recommends setting the
TTL
field for
IP
packets to 64, but many systems use smaller values
( BSD 4.3
uses 30,
BSD 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
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
BSD systems did before the
BSD 4.3 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
BSD 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
ing
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.
RETURN VALUES
The
utility returns an exit status of zero if at least one response was
heard from the specified
host
a status of two if the transmission was successful but no responses
were received; or another value
(from
In sysexits.h )
if an error occurred.
The original
utility was written by
An Mike Muuss
while at the US Army Ballistics
Research Laboratory.
BUGS
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 Ap s
not much 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.
