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In Linux, an ARP entry's age gets reset/refreshed if a packet comes by. However, it seems that FreeBSD simply sets a timer, and unconditionally evicts the ARP entry even if packets with that MAC-address/IP came by. Is there a way to get Linux's behaviour of updating the age if traffic is seen?

I am experiencing large bursts of ARP broadcast traffic every 20 minutes on my LAN because of this. I know that one can change the age in FreeBSD's cache, but that just changes the intervals between bursts. I want to stop the bursts in the first place.

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The great thing about FreeBSD is that things are documented: arp(4)

We have:

These routes time out periodically (normally 20 minutes after validated; entries are not validated when not in use)

...and...

max_age How long an ARP entry is held in the cache until it needs to be refreshed. Default is 1200 seconds.

I read that as if we see the entry within maxage then it is validated. That is: When in use it is validated.

So if you do a:

arp -i ixl0 -a
? (192.168.1.2) at 00:00:00:00:00:00 on ixl0 expires in 237 seconds [ethernet]
? (192.168.1.1) at 00:00:00:00:00:01 on ixl0 permanent [ethernet]

You will see the arp entries and their age. If you want to extend the cache duration simply change max_age.

  • I know about the max age, I've also tried to explain how this still differs from, e.g., Linux' implementation and many other platforms. I get an enormous arp broadcast storm each 20 minutes.. doesn't really matter if this is every 20min or every hour – hbogert Jan 8 at 16:25
  • I think you have a different problem. But as you have already explained everything including the required answer - good luck with that. Asking a question and including the facts might gain more traction. – Claus Andersen Jan 8 at 16:57
  • Indeed, there is a deeper problem in my scenario, but all other possible solution are a dead end. But I don't think I gave the answer myself.. unless you think I should ditch pfSense for a linux-based distro – hbogert Jan 8 at 22:04

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