Manual: ip-neighbour

IP-NEIGHBOUR(8) Linux IP-NEIGHBOUR(8)

NAME
ip-neighbour - neighbour/arp tables management.

SYNOPSIS
ip [ OPTIONS ] neigh { COMMAND | help }

ip neigh { add | del | change | replace } { ADDR [ lladdr LLADDR ] [ nud STATE ] | proxy ADDR } [ dev DEV ] [ router
] [ use ] [ managed ] [ extern_learn ] [ extern_valid ]

ip neigh { show | flush } [ proxy ] [ to PREFIX ] [ dev DEV ] [ nud STATE ] [ vrf NAME ] [ nomaster ]

ip neigh get ADDR dev DEV

STATE := { permanent | noarp | stale | reachable | none | incomplete | delay | probe | failed }

DESCRIPTION
The ip neigh command manipulates 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.

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

ip neighbour add
add a new neighbour entry

ip neighbour change
change an existing entry

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

These commands create new neighbour records or update existing ones.

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

dev NAME
the interface to which this neighbour is attached.

proxy indicates whether we are proxying for this neighbour entry

router indicates whether neighbour is a router

use this neigh entry is in "use". This option can be used to indicate to the kernel that a controller is
using this dynamic entry. If the entry does not exist, the kernel will resolve it. If it exists, an at‐
tempt to refresh the neighbor entry will be triggered.

managed
this neigh entry is "managed". This option can be used to indicate to the kernel that a controller is
using this dynamic entry. In contrast to "use", if the entry does not exist, the kernel will resolve it
and periodically attempt to auto-refresh the neighbor entry such that it remains in resolved state when
possible.

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.

extern_valid
this neigh entry was learned and determined to be valid externally. The kernel will not remove or in‐
validate the entry, but it can probe the entry and notify user space when the entry becomes reachable.
The kernel will return the entry to stale state if it did not receive a confirmation after probing the
entry.

lladdr LLADDRESS
the link layer address of the neighbour. LLADDRESS can also be null.

nud STATE
the state of the neighbour entry. nud is an abbreviation for 'Neighbour Unreachability Detection'.
The state can take one of the following values:

permanent
the neighbour entry is valid forever and can be only be removed administratively.

noarp the neighbour entry is valid. No attempts to validate this entry will be made but it can be re‐
moved when its lifetime expires.

reachable
the neighbour entry is valid until the reachability timeout expires.

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

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.

incomplete
the neighbour entry has not (yet) been validated/resolved.

delay neighbor entry validation is currently delayed.

probe neighbor is being probed.

failed max number of probes exceeded without success, neighbor validation has ultimately failed.

ip neighbour delete
delete a neighbour entry

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

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

ip neighbour show
list neighbour entries

to ADDRESS (default)
the prefix selecting the neighbours to list.

dev NAME
only list the neighbours attached to this device.

vrf NAME
only list the neighbours for given VRF.

nomaster
only list neighbours attached to an interface with no master.

proxy list neighbour proxies.

unused only list neighbours which are not currently in use.

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

ip neighbour flush
flush neighbour entries
This command has the same arguments as 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 permanent and noarp.

With the -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, ip neigh flush also
dumps all the deleted neighbours.

ip neigh get
lookup a neighbour entry to a destination given a device

proxy indicates whether we should lookup a proxy neighbour entry

to ADDRESS (default)
the prefix selecting the neighbour to query.

dev NAME
get neighbour entry attached to this device.

EXAMPLES
ip neighbour
Shows the current neighbour table in kernel.

ip neigh flush dev eth0
Removes entries in the neighbour table on device eth0.

ip neigh get 10.0.1.10 dev eth0
Performs a neighbour lookup in the kernel and returns a neighbour entry.

Manual: ip-neighbour

Related Commands: