IP-NEIGHBOUR(8)

💖 NAME 💖

okay so bestie, welcome to ip-neighbour(8) — yep, the ip-neighbour page from the Linux manual, section 8, the admin-commands section, she's iconic 💅. And what does she do? neighbour/arp tables management. that's the whole vibe. no cap. 🦋

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🌸 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 }

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✨ DESCRIPTION ✨

so the ip neigh command manipulates neighbour objects, which are basically the little bindings between protocol addresses and link layer addresses for hosts that are sharing the same link 🫶. Neighbour entries get organised into tables. and fun fact: the IPv4 neighbour table has a whole other name — the ARP table. yes, that ARP table. main character energy fr fr 👑

The corresponding commands display neighbour bindings and their properties, add new neighbour entries and delete old ones. that's the whole job description, periodt.

🎀 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. lowkey the same energy, three different names.

• 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 attempt 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. she's committed to the relationship, okay 😭
• 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 invalidate 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. yes, literally null. it's giving nothing and that's valid 🍓
• 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. forever-forever. 💜
  • 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. 👀 suspicious!! but valid!!
  • 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. rip bestie 💀

🎀 ip neighbour delete

delete a neighbour entry 🗑️

The arguments are the same as with ip neigh add, except that lladdr and nud are ignored. they simply do not get a say in this.

⚠️ 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. do NOT play with the kernel's noarp entries bestie, she bites 😭🙈

🎀 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. the unemployed entries ✨
• 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. so like, default is not those two. noted. 🫶

🎀 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. (so your forever-entries are safe from a bare flush. she's considerate.)

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. twice the -statistics, twice the drama 🍿

🎀 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.

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🌟 EXAMPLES 🌟

ip neighbour

Shows the current neighbour table in kernel. casual lil peek 👑

ip neigh flush dev eth0

Removes entries in the neighbour table on device eth0. bye besties 💅

ip neigh get 10.0.1.10 dev eth0

Performs a neighbour lookup in the kernel and returns a neighbour entry. like a little detective 🕵️‍♀️

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🦋 SEE ALSO 🦋

• ip(8)

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💜 AUTHOR 💜

Original Manpage by Michail Litvak <mci@owl.openwall.com> — thank you for the lore, we are obsessed 🫶

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and that's the whole page bestie!! this was iproute2, dated 20 Dec 2011 — yes she's an elder but she still ate and left no crumbs 👑✨ go forth and manage those neighbour tables, ily, bye!! 💖🎀🌈