.\" $USAGI: ping6.8,v 1.10 2001/10/04 09:32:39 yoshfuji Exp $
.\"
.\" Copyright (C)2000 Hideaki YOSHIFUJI / USAGI Project.
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.Dd August, 2000
.Dt PING6 8
.Os "iputils-ss991024-usagi"
.Sh NAME
.Nm ping6
.Nd send
.Tn ICMP ECHO_REQUEST
packets to network hosts
.Sh SYNOPSIS
.Nm ping6
.Op Fl ?dfLnqrRvtWN
.Op Fl 4 Ar addrtype
.Op Fl 6 Ar addrtype
.Op Fl c Ar count
.Op Fl F Ar flowinfo
.Op Fl h Ar hoplimit
.Op Fl I Ar interface
.Op Fl i Ar wait
.Op Fl J Ar subject-name
.Op Fl j Ar subject-address
.Op Fl l Ar preload
.Op Fl p Ar pattern
.Op Fl s Ar packetsize
.Op Fl T Ar traffic-class
.Op Fl w Ar wait

.Sh DESCRIPTION
.Nm
uses the
.Tn ICMPv6
protocol's mandatory
.Tn IPMP6_ECHO_REQUEST
datagram to elicit an
.Tn ICMP6_ECHO_REPLY
from a host or gateway.
.Tn ICMP6_ECHO_REQUEST
datagrams (``pings'') have an IPv6 header, 
and
.Tn ICMPv6
header formatted as documented in RFC2463.

The options are as follows:
.Bl -tag -width Ds
.It Fl 4 Ar addrtype
Generate ICMPv6 Node Information Node IPv4 Addresses query, rather than echo-request.
.Ar addrtype
must be a string constructed of the following characters.
.Bl -tag -width Ds
.It Ic -
dummy.
.It Ic a
requests all the responder's unicast addresses.
If the charater is ommited,
only those addresses which belong to the interface which has the
responder's address are requests.
.\" old ipsec
.\" .It Fl A
.\" Enables transport-mode IPsec authentication header
.\" .Pq experimental .
.El
.It Fl a Ar addrtype
Generate ICMPv6 Node Information Node Addresses query, rather than echo-request.
.Ar addrtype
must be a string constructed of the following characters.
.Bl -tag -width Ds
.It Ic -
dummy.
.It Ic 6
requests all the responder's unicast addresses.
If the charater is ommited,
only those addresses which belong to the interface which has the
responder's address are requests.
.It Ic c
requests responder's IPv4-compatible and IPv4-mapped addresses.
.It Ic g
requests responder's global-scope addresses.
.It Ic s
requests responder's site-local addresses.
.It Ic l
requests responder's link-local addresses.
.It Ic A
requests responder's anycast addresses.
Without this character, the responder will return unicast addresses only.
With this character, the responder will return anycast addresses only.
Note that the specification does not specify how to get responder's
anycast addresses.
This is an experimental option.
.El
.It Fl c Ar count
Stop after sending (and receiving)
.Ar count
.Tn ECHO_RESPONSE
packets.
.It Fl d
Set the
.Dv SO_DEBUG
option on the socket being used.
.It Fl F Ar flowinfo
Set flowinfo.
.It Fl f
Flood ping.
Outputs packets as fast as they come back or one hundred times per second,
whichever is more.
For every
.Tn ECHO_REQUEST
sent a period ``.'' is printed, while for ever
.Tn 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
.It Fl H
Disable
.Fl n
option and try to perform reverse-lookup.
.It Fl h Ar hoplimit
Set the IPv6 hoplimit.
.It Fl I Ar interface
Source packets with the given interface address.
This flag applies if the ping destination is a multicast address,
or link-local/site-local unicast address.
.It Fl i Ar wait
Wait
.Ar wait
seconds
.Em between sending each packet .
The default is to wait for one second between each packet.
This option is incompatible with the
.Fl f
option.
.It Fl J Ar subject-name
Set subject name for node information queries.
.It Fl j Ar subject-address
Set subject address for node information queries.
.It Fl l Ar preload
If
.Ar preload
is specified,
.Nm
sends that many packets as fast as possible before falling into its normal
mode of behavior.
Only the super-user may use this option.
.It Fl N
Probe node information multicast group
.Pq Li ff02::2:xxxx:xxxx .
.Ar host
must be string hostname of the target
.Pq must not be a numeric IPv6 address .
Node information multicast group will be computed based on given
.Ar host ,
and will be used as the final destination.
Since node information multicast group is a link-local multicast group,
destination link needs to be specified by
.Fl I
option.
.It Fl n
Numeric output only.
No attempt will be made to lookup symbolic names for addresses in the reply.
This option is enabled by default, and if you want to disable this option
to look-up symbolic names, use 
.Fl H 
option.
.It Fl p Ar 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,
.Dq Li \-p ff
will cause the sent packet to be filled with all
ones.
.It Fl q
Quiet output.
Nothing is displayed except the summary lines at startup time and
when finished.
.It Fl R
Record route.
Includes the
.Tn RECORD_ROUTE
option in the
.Tn 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.
.It Fl 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 ping6 a local host through an interface
that has no route through it (e.g., after the interface was dropped by
.Xr routed 8 ) .
.It Fl s Ar packetsize
Specifies the number of data bytes to be sent.  
The default is 56, which translates into 64
.Tn ICMP
data bytes when combined
with the 8 bytes of
.Tn ICMP
header data.
.It Fl T
Set the IPv6 traffic class.
.It Fl t
Generate ICMPv6 Node Information supported query types query,
rather than echo-request.
.It Fl U
Print true user-to-user latency (the old behaviour).
.It Fl v
Verbose output.
.It Fl W
Generate ICMPv6 Node Information DNS Name query, rather than echo-request.
.Fl s
has no effect if
.Fl W
is specified.
.Tn ICMP
packets other than
.Tn ECHO_RESPONSE
that are received are listed.
.El
.Pp
When using
.Nm
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 round-trip time numbers.
When the specified number of packets have been sent (and received) or
if the program is terminated with a
.Dv SIGINT ,
a brief summary is displayed.
.Pp
If 
.Nm
does not receive any reply packets at all it will exit with code 1.
On 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.
.Pp
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
.Nm
during normal operations or from automated scripts.
.\" .Sh ICMP PACKET DETAILS
.\" An IP header without options is 20 bytes.
.\" An
.\" .Tn ICMP
.\" .Tn ECHO_REQUEST
.\" packet contains an additional 8 bytes worth
.\" of
.\" .Tn ICMP
.\" header followed by an arbitrary amount of data.
.\" When a
.\" .Ar 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
.\" .Tn ICMP
.\" .Tn ECHO_REPLY
.\" will always be 8 bytes more than the requested data space
.\" (the
.\" .Tn ICMP
.\" header).
.\" .Pp
.\" If the data space is at least eight bytes large,
.\" .Nm ping
.\" 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.
.Sh DUPLICATE AND DAMAGED PACKETS
.Nm Ping6
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.
.Pp
Damaged packets are obviously serious cause for alarm and often
indicate broken hardware somewhere in the
.Nm ping
packet's path (in the network or in the hosts).
.Sh 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.
.Pp
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
.Fl p
option of
.Nm ping6.
.Sh TTL DETAILS
The
.Tn 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
.Tn TTL
field by exactly one.
.Pp
The
.Tn TCP/IP
specification states that the
.Tn TTL
field for
.Tn TCP
packets should
be set to 60, but many systems use smaller values (4.3
.Tn BSD
uses 30, 4.2 used
15).
.Pp
The maximum possible value of this field is 255, and most Unix systems set
the
.Tn TTL
field of
.Tn ICMP ECHO_REQUEST
packets to 255.
This is why you will find you can ``Ping'' some hosts, but not reach them
with
.Xr telnet 1
or
.Xr ftp 1 .
.Pp
In normal operation ping6 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
.Tn TTL
field in its response:
.Bl -bullet
.It
Not change it; this is what Berkeley Unix systems did before the
.Bx 4.3 tahoe
release.
In this case the
.Tn TTL
value in the received packet will be 255 minus the
number of routers in the round-trip path.
.It
Set it to 255; this is what current Berkeley Unix systems do.
In this case the
.Tn TTL
value in the received packet will be 255 minus the
number of routers in the path
.Xr from
the remote system
.Em to
the
.Nm ping Ns Em ing
host.
.It
Set it to some other value.
Some machines use the same value for
.Tn ICMP
packets that they use for
.Tn TCP
packets, for example either 30 or 60.
Others may use completely wild values.
.El
.Sh BUGS
Many Hosts and Gateways ignore the
.Tn RECORD_ROUTE
option.
.Pp
The maximum IP header length is too small for options like
.Tn RECORD_ROUTE
to
be completely useful.
There's not much that that can be done about this, however.
.Pp
Flood pinging is not recommended in general, and flood pinging the
broadcast address should only be done under very controlled conditions.
.Sh SEE ALSO
.Xr netstat 1 ,
.Xr ifconfig 8 ,
.Xr ping 8
.Rs
.%A A. Conta
.%A S. Deering
.%T "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification"
.%N RFC2463
.%D December 1998
.Re
.Rs
.%A Matt Crawford
.%T "IPv6 Node Information Queries"
.%N draft-ietf-ipngwg-icmp-name-lookups-06.txt
.%D July 2000
.%O work in progress material
.Re
.Sh HISTORY
The
.Nm ping
command appeared in
.Bx 4.3 .
