SYNOPSIS
ping [ -LRUbdfnqrvVaAB] [ -c count] [ -i interval] [ -l
preload] [ -p pattern] [ -s packetsize] [ -t ttl] [ -w
deadline] [ -F flowlabel] [ -I interface] [ -M hint] [
-Q tos] [ -S sndbuf] [ -T timestamp option] [ -W time
out] [ hop ...] destination
DESCRIPTION
ping uses the ICMP protocol's mandatory ECHO_REQUEST data
gram to elicit an ICMP ECHO_RESPONSE from a host or gate
way. 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.
OPTIONS
-a Audible ping.
-A Adaptive ping. Interpacket interval adapts to
round-trip time, so that effectively not more than
one (or more, if preload is set) unanswered probes
present in the network. Minimal interval is 200msec
for not super-user. On networks with low rtt this
mode is essentially equivalent to flood mode.
-b Allow pinging a broadcast address.
-B Do not allow ping to change source address of
probes. The address is bound to one selected when
ping starts.
-c count
Stop after sending count ECHO_REQUEST packets. With
deadline option, ping waits for count ECHO_REPLY
packets, until the timeout expires.
-d Set the SO_DEBUG option on the socket being used.
Essentially, this socket option is not used by
Linux kernel.
-F flow label
Allocate and set 20 bit flow label on echo request
packets. (Only ping6). If value is zero, kernel
allocates random flow label.
-f Flood ping. For every ECHO_REQUEST sent a period
``.'' is printed, while for ever ECHO_REPLY
received a backspace is printed. This provides a
rapid display of how many packets are being
dropped. If interval is not given, it sets inter
val to zero and outputs packets as fast as they
device. When pinging IPv6 link-local address this
option is required.
-l preload
If preload is specified, ping sends that many pack
ets not waiting for reply. Only the super-user may
select preload more than 3.
-L Suppress loopback of multicast packets. This flag
only applies if the ping destination is a multicast
address.
-n Numeric output only. No attempt will be made to
lookup symbolic names for host addresses.
-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 tos Set Quality of Service -related bits in ICMP data
grams. tos can be either decimal or hex number.
Traditionally (RFC1349), these have been inter
preted as: 0 for reserved (currently being rede
fined as congestion control), 1-4 for Type of Ser
vice and 5-7 for Precedence. Possible settings for
Type of Service are: minimal cost: 0x02, reliabil
ity: 0x04, throughput: 0x08, low delay: 0x10. Mul
tiple TOS bits should not be set simultaneously.
Possible settings for special Precedence range from
priority (0x20) to net control (0xe0). You must be
root (CAP_NET_ADMIN capability) to use Critical or
higher precedence value. You cannot set bit 0x01
(reserved) unless ECN has been enabled in the ker
nel. In RFC2474, these fields has been redefined
as 8-bit Differentiated Services (DS), consisting
of: bits 0-1 of separate data (ECN will be used,
here), and bits 2-7 of Differentiated Services
Codepoint (DSCP).
-q Quiet output. Nothing is displayed except the sum
mary lines at startup time and when finished.
-R Record route. (IPv4 only) 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 Bypass the normal routing tables and send directly
to buffer not more than one packet.
-t ttl Set the IP Time to Live.
-T timestamp option
Set special IP timestamp options. timestamp option
may be either tsonly (only timestamps), tsandaddr
(timestamps and addresses) or tsprespec host1
[host2 [host3 [host4]]] (timestamp prespecified
hops).
-M hint
Select Path MTU Discovery strategy. hint may be
either do (prohibit fragmentation, even local one),
want (do PMTU discovery, fragment locally when
packet size is large), or dont (do not set DF
flag).
-U Print full user-to-user latency (the old
behaviour). Normally ping prints network round trip
time, which can be different f.e. due to DNS fail
ures.
-v Verbose output.
-V Show version and exit.
-w deadline
Specify a timeout, in seconds, before ping exits
regardless of how many packets have been sent or
received. In this case ping does not stop after
count packet are sent, it waits either for deadline
expire or until count probes are answered or for
some error notification from network.
-W timeout
Time to wait for a response, in seconds. The option
affects only timeout in absense of any responses,
otherwise ping waits for two RTTs.
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 fur
ther and further away should be ``pinged''. Round-trip
times and packet loss statistics are computed. If dupli
cate 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/aver
age/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. Shorter current statistics can be obtained
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 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 of size of struct timeval
ping uses the beginning bytes of this space to include a
timestamp which it uses in the computation of round trip
times. If the data space is shorter, no round trip times
are given.
DUPLICATE AND DAMAGED PACKETS
ping will report duplicate and damaged packets. Duplicate
packets should never occur, and seem to be caused by inap
propriate 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).
TRYING DIFFERENT DATA PATTERNS
The (inter)network layer should never treat packets dif
ferently depending on the data contained in the data por
tion. Unfortunately, data-dependent problems have been
known to sneak into networks and remain undetected for
long periods of time. In many cases the particular pat
tern 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 pat
tern 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.
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 num
ber of routers in the round-trip path.
· Set it to 255; this is what current Berkeley Unix sys
tems 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.
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'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.
SEE ALSO
netstat(1), ifconfig(8).
HISTORY
The ping command appeared in 4.3BSD.
The version described here is its descendant specific to
Linux.
SECURITY
ping requires CAP_NET_RAWIO capability to be executed. It
may be used as set-uid root.
AVAILABILITY
ping is part of iputils package and the latest versions
are available in source form for anonymous ftp
ftp://ftp.inr.ac.ru/ip-routing/iputils-current.tar.gz.
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