The ip neighborhood command can be used to view the arp cache. In this example, there are a few records with the IP address, MAC address, and state of known hosts.

[root@server1 ~]# ip neighborhood
192.168.0.101 dev eth0 lladdr 00:25:b4:cf:3e:81 REACHABLE
192.168.0.102 dev eth0 lladdr 00:25:b4:de:4a:25 STALE
192.168.0.103 dev eth0 lladdr 00:25:b4:a1:37:b4 DELAY

• REACHABLE = The IP address to MAC address resolution is valid.
• STALE = The IP address to MAC address resolution is valid but probalby unreachable. 
• DELAY = The IP address to MAC address resolution is not valid.

The ip neighborhood can be shortened to just ip n.

[root@server1 ~]# ip n
192.168.0.101 dev eth0 lladdr 00:25:b4:cf:3e:81 REACHABLE
192.168.0.102 dev eth0 lladdr 00:25:b4:de:4a:25 STALE
192.168.0.103 dev eth0 lladdr 00:25:b4:a1:37:b4 DELAY

Adding records

The ip neighborhood add command can be used to add a record to the ARP cache.

[root@server1 ~]# ip neighborhood add 192.168.0.104 lladdr 00:25:b4:b2:25:c1 dev eth0 nud permanent

Notice the last field in "permanent". Possible options are:

• permanent
• noarp
• stale
• reachable

Deleting records

The ip neighborhood del command can be used to delete a record from the ARP cache.

[root@server1 ~]# ip neighborhood del 192.168.0.104 dev eth0

Modify record

The ip neighborhood chg command can be used to modify a records in the ARP cache. For example, to change the state from stale to reachable:

[root@server1 ~]# ip neighborhood chg 192.168.0.102 dev eth0 nud reachable