ping - phpMan

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 unless 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 every
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. Real number allowed with dot as a
decimal separator (regardless locale setup). 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 2 ms.

-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. Do not suppress DUP replies when pinging multicast address.

-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. Real number allowed with dot as a
decimal separator (regardless locale setup). 0 means infinite timeout.

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.

Population standard 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 indicates 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.