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 ] [ extern_learn ]
ip neigh { show | flush } [ proxy ] [ to PREFIX ] [ dev DEV ] [ nud STATE ] [ vrf NAME ]
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 neigbour entry
- router
indicates whether neigbour is a router
- 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.
- 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 removed 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 neighbour 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 address 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.
- 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.
Examples
ip neighbour
Shows the current neighbour table in kernel.
ip neigh flush dev eth0
Removes entries in the neighbour table on device eth0.