ping Man page

PING(8) System Manager’s Manual: iputils PING(8)

NAME

ping, ping6 – send ICMP ECHO_REQUEST to network hosts

SYNOPSIS

ping [-aAbBdDfhLnOqrRUvV] [-c count] [-F flowlabel] [-i interval] [-I
interface] [-l preload] [-m mark] [-M pmtudisc_option] [-N node‐
info_option] [-w deadline] [-W timeout] [-p pattern] [-Q tos] [-s pack‐
etsize] [-S sndbuf] [-t ttl] [-T timestamp option] [hop …] destina‐
tion

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.

ping6 is IPv6 version of ping, and can also send Node Information
Queries (RFC4620). Intermediate hops may not be allowed, because IPv6
source routing was deprecated (RFC5095).

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 probe is present in the network. Minimal inter‐
val 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 time‐
out 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 hun‐
dred times per second, whichever is more. Only the super-user
may use this option with zero interval.

-F flow label
ping6 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 val‐
ues less 0.2 seconds.

-I interface
interface is either an address, or an interface name. If inter‐
face is an address, it sets source address to specified inter‐
face address. If interface in an interface name, it sets source
interface to specified interface. For ping6, when doing ping to
a link-local scope address, link specification (by the ‘%’-nota‐
tion in destination, or by this option) is required.

-l preload
If preload is specified, ping sends that many packets not wait‐
ing 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 vari‐
ety 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
ping6 only. Send ICMPv6 Node Information Queries (RFC4620),
instead of Echo Request.

help Show help for NI support.

name Queries for Node Names.

ipv6 Queries for IPv6 Addresses. There are several IPv6 spe‐
cific 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 sepa‐
rate data, and bits 2-7 (highest 6 bits) of Differentiated Ser‐
vices Codepoint (DSCP). In RFC2481 and RFC3168, bits 0-1 are
used for ECN.

Historically (RFC1349, obsoleted by RFC2474), these were inter‐
preted 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 run‐
ning. 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 dis‐
played. 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 indi‐
cate 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 depend‐
ing 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 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 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 trans‐
mit 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 man‐
age 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 decre‐
ment 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 tel‐
net 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 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.

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 condi‐
tions.

SEE ALSO

netstat, 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_RAW 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 at http://www.skbuff.net/iputils/iputils-cur‐
rent.tar.bz2.

iputils-121221 07 May 2014 PING(8)

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