This read-only Counter counts how many times a hash chain in the address table has completely filled up, meaning a new station's MAC address couldn't be learned and had to be treated as unknown. A nonzero value here directly correlates with an uptick in ciscoTsPortStatsUnknownStaFrames on affected ports, since frames from or to unlearnable stations get punted to software instead of hardware-switched. This counter incrementing steadily is a concrete signal that the switch's address table can no longer keep up with the number of active stations.