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====== Linux ARP table ======

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

Files related to ARP cache 
<cli prompt='$'>
/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
</cli>

  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",
<cli prompt='$'>
pherricoxide@midigaurd:~$ 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
</cli>

To mark entries as invalid, but not remove them from the cache
<cli prompt='$'>
$ ip -s -s neigh flush all
</cli>

To delete a particular entry 
<cli prompt='$'>
$ arp -d <ip_address>
</cli>


<cli prompt='$'>
$ ip link set arp off dev eth0; ip link set arp on dev eth0
</cli>

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
<cli prompt='$'>
$ 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
</cli>
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