.TH IP\-NEIGHBOUR 8 "20 Dec 2011" "iproute2" "Linux"
.SH "NAME"
ip-neighbour \- neighbour/arp tables management.
.SH "SYNOPSIS"
.sp
.ad l
.in +8
.ti -8
.B ip
.RI "[ " OPTIONS " ]"
.B neigh
.RI " { " COMMAND " | "
.BR help " }"
.sp

.ti -8
.BR "ip neigh" " { " add " | " del " | " change " | " replace " } { "
.IR ADDR " [ "
.B  lladdr
.IR LLADDR " ] [ "
.BR nud " { " permanent " | " noarp " | " stale " | " reachable " } ] | " proxy
.IR ADDR " } [ "
.B  dev
.IR DEV " ]"

.ti -8
.BR "ip neigh" " { " show " | " flush " } [ " to
.IR PREFIX " ] [ "
.B  dev
.IR DEV " ] [ "
.B  nud
.IR STATE " ]"


.SH DESCRIPTION
The 
.B ip neigh
command manipulates 
.I neighbour
objects that establish bindings between protocol addresses and
link layer addresses for hosts sharing the same link.
Neighbour entries are organized into tables. The IPv4 neighbour table
is known by another name - the ARP table.

.P
The corresponding commands display neighbour bindings
and their properties, add new neighbour entries and delete old ones.

.SS ip neighbour add - add a new neighbour entry
.SS ip neighbour change - change an existing entry
.SS ip neighbour replace - add a new entry or change an existing one

These commands create new neighbour records or update existing ones.

.TP
.BI to " ADDRESS " (default)
the protocol address of the neighbour. It is either an IPv4 or IPv6 address.

.TP
.BI dev " NAME"
the interface to which this neighbour is attached.

.TP
.BI lladdr " LLADDRESS"
the link layer address of the neighbour.
.I LLADDRESS
can also be
.BR "null" .

.TP
.BI nud " NUD_STATE"
the state of the neighbour entry.
.B nud
is an abbreviation for 'Neighbour Unreachability Detection'.
The state can take one of the following values:

.in +8
.B permanent
- the neighbour entry is valid forever and can be only
be removed administratively.
.sp

.B noarp
- the neighbour entry is valid. No attempts to validate
this entry will be made but it can be removed when its lifetime expires.
.sp

.B reachable
- the neighbour entry is valid until the reachability
timeout expires.
.sp

.B stale
- the neighbour entry is valid but suspicious.
This option to
.B ip neigh
does not change the neighbour state if it was valid and the address
is not changed by this command.
.in -8

.SS ip neighbour delete - delete a neighbour entry
This command invalidates a neighbour entry.

.PP
The arguments are the same as with
.BR "ip neigh add" ,
except that
.B lladdr
and
.B nud
are ignored.

.PP
.B Warning:
Attempts to delete or manually change a
.B noarp
entry created by the kernel may result in unpredictable behaviour.
Particularly, the kernel may try to resolve this address even
on a
.B NOARP
interface or if the address is multicast or broadcast.

.SS ip neighbour show - list neighbour entries

This commands displays neighbour tables.

.TP
.BI to " ADDRESS " (default)
the prefix selecting the neighbours to list.

.TP
.BI dev " NAME"
only list the neighbours attached to this device.

.TP
.B unused
only list neighbours which are not currently in use.

.TP
.BI nud " NUD_STATE"
only list neighbour entries in this state.
.I NUD_STATE
takes values listed below or the special value
.B all
which means all states.  This option may occur more than once.
If this option is absent,
.B ip
lists all entries except for
.B none
and
.BR "noarp" .

.SS ip neighbour flush - flush neighbour entries
This command flushes neighbour tables, selecting
entries to flush by some criteria.

.PP
This command has the same arguments as
.B show.
The differences are that it does not run when no arguments are given,
and that the default neighbour states to be flushed do not include
.B permanent
and
.BR "noarp" .

.PP
With the
.B -statistics
option, the command becomes verbose.  It prints out the number of
deleted neighbours and the number of rounds made to flush the
neighbour table.  If the option is given
twice,
.B ip neigh flush
also dumps all the deleted neighbours.

.SH EXAMPLES
.PP
ip neighbour
.RS
Shows the current neighbour table in kernel.
.RE
.PP
ip neigh flush dev eth0
.RS
Removes entries in the neighbour table on device eth0.
.RE

.SH SEE ALSO
.br
.BR ip (8)

.SH AUTHOR
Original Manpage by Michail Litvak <mci@owl.openwall.com>