PING(8) iputils PING(8)
NAME
ping - send ICMP ECHO_REQUEST to network hosts
SYNOPSIS
ping [-aAbBdDfhLnOqrRUvV46] [-c count] [-F flowlabel] [-i interval]
[-I interface] [-l preload] [-m mark] [-M pmtudisc_option]
[-N nodeinfo_option] [-w deadline] [-W timeout] [-p pattern]
[-Q tos] [-s packetsize] [-S sndbuf] [-t ttl]
[-T timestamp option] [hop...] destination
DESCRIPTION
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.
ping works with both IPv4 and IPv6. Using only one of them explicitly
can be enforced by specifying -4 or -6.
ping can also send IPv6 Node Information Queries (RFC4620).
Intermediate hops may not be allowed, because IPv6 source routing was
deprecated (RFC5095).
OPTIONS
-4
Use IPv4 only.
-6
Use IPv6 only.
-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 probe is 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.
-D
Print timestamp (unix time + microseconds as in gettimeofday)
before each line.
-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 interval to zero and outputs packets
as fast as they come back or one hundred times per second,
whichever is more. Only the super-user may use this option with
zero interval.
-F flow label
IPv6 only. Allocate and set 20 bit flow label (in hex) on echo
request packets. If value is zero, kernel allocates random flow
label.
-h
Show help.
-i interval
Wait interval seconds between sending each packet. The default is
to wait for one second between each packet normally, or not to wait
in flood mode. Only super-user may set interval to values less than
0.2 seconds.
-I interface
interface is either an address, an interface name or a VRF name. If
interface is an address, it sets source address to specified
interface address. If interface is an interface name, it sets
source interface to specified interface. If interface is a VRF
name, each packet is routed using the corresponding routing table;
in this case, the -I option can be repeated to specify a source
address. NOTE: For IPv6, when doing ping to a link-local scope
address, link specification (by the '%'-notation in destination, or
by this option) can be used but it is no longer required.
-l preload
If preload is specified, ping sends that many packets 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.
-m mark
use mark to tag the packets going out. This is useful for variety
of reasons within the kernel such as using policy routing to select
specific outbound processing.
-M pmtudisc_opt
Select Path MTU Discovery strategy. pmtudisc_option 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).
-N nodeinfo_option
IPv6 only. Send ICMPv6 Node Information Queries (RFC4620), instead
of Echo Request. CAP_NET_RAW capability is required.
help
Show help for NI support.
name
Queries for Node Names.
ipv6
Queries for IPv6 Addresses. There are several IPv6 specific
flags.
ipv6-global
Request IPv6 global-scope addresses.
ipv6-sitelocal
Request IPv6 site-local addresses.
ipv6-linklocal
Request IPv6 link-local addresses.
ipv6-all
Request IPv6 addresses on other interfaces.
ipv4
Queries for IPv4 Addresses. There is one IPv4 specific flag.
ipv4-all
Request IPv4 addresses on other interfaces.
subject-ipv6=ipv6addr
IPv6 subject address.
subject-ipv4=ipv4addr
IPv4 subject address.
subject-name=nodename
Subject name. If it contains more than one dot, fully-qualified
domain name is assumed.
subject-fqdn=nodename
Subject name. Fully-qualified domain name is always assumed.
-n
Numeric output only. No attempt will be made to lookup symbolic
names for host addresses.
-O
Report outstanding ICMP ECHO reply before sending next packet. This
is useful together with the timestamp -D to log output to a
diagnostic file and search for missing answers.
-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
Quiet output. Nothing is displayed except the summary lines at
startup time and when finished.
-Q tos
Set Quality of Service -related bits in ICMP datagrams. tos can be
decimal (ping only) or hex number.
In RFC2474, these fields are interpreted as 8-bit Differentiated
Services (DS), consisting of: bits 0-1 (2 lowest bits) of separate
data, and bits 2-7 (highest 6 bits) of Differentiated Services
Codepoint (DSCP). In RFC2481 and RFC3168, bits 0-1 are used for
ECN.
Historically (RFC1349, obsoleted by RFC2474), these were
interpreted as: bit 0 (lowest bit) for reserved (currently being
redefined as congestion control), 1-4 for Type of Service and bits
5-7 (highest bits) for Precedence.
-r
Bypass the normal routing tables and send directly to a host on an
attached interface. 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
provided the option -I is also used.
-R
ping only. 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.
-s 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.
-S sndbuf
Set socket sndbuf. If not specified, it is selected to buffer not
more than one packet.
-t ttl
ping only. 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).
-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 failures.
-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 absence 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 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/mdev round-trip time
numbers.
Median deviation (mdev), essentially an average of how far each ping
RTT is from the mean RTT. The higher mdev is, the more variable the RTT
is (over time). With a high RTT variability, you will have speed issues
with bulk transfers (they will take longer than is strictly speaking
necessary, as the variability will eventually cause the sender to wait
for ACKs) and you will have middling to poor VoIP quality.
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 without
termination of process with signal SIGQUIT.
If ping does not receive any reply packets at all it will exit with
code 1. If a packet count and deadline are both specified, and fewer
than count packets are received by the time the deadline has arrived,
it will also exit with code 1. On other error it exits with code 2.
Otherwise it exits with code 0. This makes it possible to use the exit
code to see if a host is alive or not.
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
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 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).
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 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.
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 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:
o 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.
o 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.
o 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
o Many Hosts and Gateways ignore the RECORD_ROUTE option.
o The maximum IP header length is too small for options like
RECORD_ROUTE to be completely useful. There's not much that can be
done about this, however.
o Flood pinging is not recommended in general, and flood pinging
the broadcast address should only be done under very controlled
conditions.
SEE ALSO
ip(8), ss(8).
HISTORY
The ping command appeared in 4.3BSD.
The version described here is its descendant specific to Linux.
As of version s20150815, the ping6 binary doesn't exist anymore. It has
been merged into ping. Creating a symlink named ping6 pointing to ping
will result in the same funcionality as before.
SECURITY
ping requires CAP_NET_RAW capability to be executed 1) if the program
is used for non-echo queries (See -N option), or 2) if kernel does not
support non-raw ICMP sockets, or 3) if the user is not allowed to
create an ICMP echo socket. The program may be used as set-uid root.
AVAILABILITY
ping is part of iputils package.
iputils s20180629 PING(8)
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