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.Dd $Mdocdate: April 15 2017 $
.Dt NDP 8
.Os
.Sh NAME
.Nm ndp
.Nd control/diagnose IPv6 Neighbor Discovery Protocol (NDP)
.Sh SYNOPSIS
.Nm ndp
.Op Fl nrt
.Op Fl a | c | p
.Op Fl H | P | R
.Op Fl A Ar wait
.Op Fl d Ar hostname
.Op Fl f Ar filename
.Op Fl i Ar interface Op Ar flag ...
.Op Fl s Ar nodename ether_addr Oo Cm temp Oc Op Cm proxy
.Op Fl V Ar rdomain
.Op Ar hostname
.Sh DESCRIPTION
The
.Nm
command manipulates the address mapping table
used by the Neighbor Discovery Protocol (NDP).
.Bl -tag -width Ds
.It Fl A Ar wait
Repeat
.Fl a
.Pq dump NDP entries
every
.Ar wait
seconds.
.It Fl a
Dump the currently existing NDP entries.
The following information will be printed:
.Bl -tag -width Ds -offset 3n
.It Neighbor
The IPv6 address of the neighbor.
.It Linklayer Address
The linklayer address of the neighbor.
If the address is not available,
it will be displayed as
.Dq (incomplete) .
.It Netif
The network interface associated with the neighbor cache entry.
.It Expire
The time until expiry of the entry.
If the entry is marked
.Dq permanent ,
it will never expire.
.It S
The state of the neighbor cache entry, as a single letter:
.Pp
.Bl -tag -width Ds -offset 3n -compact
.It D
Delay
.It I
Incomplete
.It N
Nostate
.It P
Probe
.It R
Reachable
.It S
Stale
.It W
Waitdelete
.It \&?
Unknown state (should never happen).
.El
.It Flags
Flags on the neighbor cache entry, in a single letter.
They are: local
.Pq Sq l ,
Router
.Pq Sq R
and proxy neighbor advertisement
.Pq Sq p .
This field may be followed by a decimal number,
representing the number of NS probes
the node has sent during the current state.
.El
.It Fl c
Erase all the NDP entries.
.It Fl d Ar hostname
Delete the specified NDP entry.
.It Fl f Ar filename
Parse entries from
.Ar file
to be inserted in the neighbor cache.
See the
.Fl s
option for a description of the file format.
.It Fl H
Harmonize consistency between the routing table and the default router
list; install the top entry of the list into the kernel routing table.
.It Fl i Ar interface Op Ar flag ...
View ND information for the specified interface.
If additional arguments are given,
.Nm
sets or clears the specified flags for the interface.
Each flag should be separated by whitespace or tab characters.
Possible flags are as follows.
All of the flags can begin with the
special character
.Ql - ,
which means the flag should be cleared.
Note that
.Fl -
would be needed before
.Fl foo
in this case.
.Bl -tag -width Ds
.It Ic nud
Turn on or off NUD (Neighbor Unreachability Detection) on the
interface.
NUD is usually turned on by default.
.It Ic accept_rtadv
Specify whether or not to accept Router Advertisement messages
received on the
.Ar interface .
Note that the kernel does not accept Router Advertisement messages
unless the interface is configured for inet6 autoconfiguration.
.El
.It Fl n
Do not try to resolve numeric addresses to hostnames.
.It Fl P
Flush all the entries in the prefix list.
.It Fl p
Show the prefix list.
.It Fl R
Flush all the entries in the default router list.
.It Fl r
Show the default router list.
.It Xo
.Fl s Ar nodename ether_addr
.Op Cm temp
.Op Cm proxy
.Xc
Register an NDP entry for the node called nodename with the Ether
address ether_addr.
The Ethernet address is given as six hexadecimal bytes separated by
colons.
The entry will be permanent unless the word
.Cm temp
is given in the command.
If the word
.Cm proxy
is given, this system will act as an ND Proxy server,
responding to requests for
.Ar nodename
even though the node address is not its own.
.It Fl t
Print a timestamp on each entry,
making it possible to merge output with
.Xr tcpdump 8 .
Most useful when used with
.Fl A .
.It Fl V Ar rdomain
Select the routing domain.
.El
.Sh EXIT STATUS
.Ex -std ndp
.Sh SEE ALSO
.Xr ip6 4 ,
.Xr sysctl.conf 5 ,
.Xr arp 8 ,
.Xr sysctl 8 ,
.Xr tcpdump 8
.Sh HISTORY
The
.Nm
command first appeared in the WIDE Hydrangea IPv6 protocol stack kit.