I know how to setup how long arp entry are cached. But - how to check how long specific entry will stay in arp table, and when next arp request will be made or arp entry disapear from table/ change status from REACHABLE to STALE?
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i've found partial answer on stackoverflow.com/questions/15372011/… - ip -s n show when ip was lastly communicated.– undefineSep 25, 2015 at 15:49
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1 Answer
There is no way to find time when is, some kind of log, arp table populated with new entry.
You can run tcpdump and watch or you can install arpwatch and see.
Arp table is writen to /proc/net/arp.
Time when some entry will be deleted from arp table depends of base_reachable_time and gc_interval. In most cases after some entry is added to arp table, after last communication and last live packet start base_reachable_time. When this time expired without new packets mac address change status. On that time system start to count gc_interval time aka if some entry is no used garbage collector will delete them but only if ...
To long story. You can not find exactly time from add action and also can not known exact time of deletion from arp table.
