close arp entry after node become unavailable

Hello,
  I noticed, that NAV does not close arp entries after monitored node
become unavailable. For example: There is an active mac address
11:22:33:44:55:66 with end_time set to infinity. When the monitored node
goes down, the mac address remains in active state, so you can find it
using machinetracker as a still active address, which apparently is not
true.

I suggest, that there should be another rule in database, enssuring that
arp entries will be closed.

Something like:

CREATE OR REPLACE RULE netbox_status_close_arp AS ON UPDATE TO netbox
  WHERE NEW.up='n'
  DO UPDATE arp SET end_time=NOW()
    WHERE netboxid=OLD.netboxid AND end_time='infinity';

Regards,

Matej