Arp table

[nulkarp]

I wonder how much time arp table refresh?

I want to save records of Arp

For this, I need to know the time of renewal.

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Sorry for my bad english.

[dennylin93]

I think net-mgmt/arpwatch is what you're looking for.

[DutchDaemon]

arp

MIB Variables
The ARP protocol implements a number of configrable variables in
net.link.ether.inet branch of the sysctl(3) MIB.

max_age How long an ARP entry is held in the cache until it needs
to be refreshed.

$ sysctl -n net.link.ether.inet.max_age
1200

I know of no direct way to query a specific arp entry for 'how old it is', and I gather that each arp entry lives at most 20 minutes (1200 seconds) before it needs to be refreshed. So running a cron job that saves records (arp -a) every ~20 minutes may work.