.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 " ] [ "
.B nud
.IR STATE " ] |"
.B proxy
.IR ADDR " } [ "
.B  dev
.IR DEV " ] [ "
.BR router " ] [ "
.BR extern_learn " ]"

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

.ti -8
.IR STATE " := {"
.BR permanent " | " noarp " | " stale " | " reachable " | " none " |"
.BR incomplete " | " delay " | " probe " | " failed " }"

.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 also 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.

.TP
ip neighbour add
add a new neighbour entry
.TP
ip neighbour change
change an existing entry
.TP
ip neighbour replace
add a new entry or change an existing one
.RS
.PP
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 proxy
indicates whether we are proxying for this neigbour entry

.TP
.BI router
indicates whether neigbour is a router

.TP
.BI extern_learn
this neigh entry was learned externally. This option can be used to
indicate to the kernel that this is a controller learnt dynamic entry.
Kernel will not gc such an entry.

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

.TP
.BI 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:

.RS
.TP
.B permanent
the neighbour entry is valid forever and can be only
be removed administratively.
.TP
.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.
.TP
.B reachable
the neighbour entry is valid until the reachability
timeout expires.
.TP
.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.
.TP
.B none
this is a pseudo state used when initially creating a neighbour entry or after
trying to remove it before it becomes free to do so.
.TP
.B incomplete
the neighbour entry has not (yet) been validated/resolved.
.TP
.B delay
neighbor entry validation is currently delayed.
.TP
.B probe
neighbor is being probed.
.TP
.B failed
max number of probes exceeded without success, neighbor validation has
ultimately failed.
.RE
.RE

.TP
ip neighbour delete
delete a neighbour entry
.RS
.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.
.RE

.TP
ip neighbour show
list neighbour entries
.RS
.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
.BI vrf " NAME"
only list the neighbours for given VRF.

.TP
.BI proxy
list neighbour proxies.

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

.TP
.BI 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" .
.RE

.TP
ip neighbour flush
flush neighbour entries
.RS
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.
.RE

.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>