https://stackoverflow.com/questions/15372011/configuring-arp-age-timeout

Files related to ARP cache

/proc/sys/net/ipv4/neigh/default/gc_interval
/proc/sys/net/ipv4/neigh/default/gc_stale_time
/proc/sys/net/ipv4/route/gc_interval
/proc/sys/net/ipv4/route/gc_timeout

gc_timeout seconds
gc_stale_time seconds

There are subtle differences between an neighbor cache entry actually falling out of the cache entirely or just being marked as stale/invalid. At some point between base_reachable_time/2 and 3*base_reachable_time/2, the entry will still be in the cache, but it will be marked with a state of STALE. You should be able to view the state with “ip -s neighbor show”,

pherricoxide@midigaurd:~$ ip -s neighbor list
192.168.42.1 dev eth0 lladdr 00:25:90:7d:7e:cd ref 2 used 184/184/139 probes 4 STALE
192.168.10.2 dev eth0 lladdr 00:1c:23:cf:0b:6a ref 3 used 33/28/0 probes 1 REACHABLE
192.168.10.1 dev eth0 lladdr 00:17:c5:d8:90:a4 ref 219 used 275/4/121 probes 1 REACHABLE

To mark entries as invalid, but not remove them from the cache

$ ip -s -s neigh flush all

To delete a particular entry

$ arp -d <ip_address>

$ ip link set arp off dev eth0; ip link set arp on dev eth0

The simplest way to completely clean the arp cache is to bring the interface down and then up again.

Else you can also change the cache timeout

$ echo 30 > /proc/sys/net/ipv4/neigh/default/gc_stale_time
$ echo 175 > /proc/sys/net/ipv4/route/gc_timeout
$ echo 20000 > /proc/sys/net/ipv4/neigh/default/base_reachable_time_ms
$ echo 30 > /proc/sys/net/ipv4/route/gc_interval