When a MAC is learned on a VLAN, an FDB entry is created for this MAC VLAN combination.Once an FDB entry is created, the aging counter in the "show fdb" output increases from 0 to “polling inteval”.
The hardware is checked every “polling interval” seconds to see if there is traffic flow from the given FDB entry.If there is a traffic flow from this MAC, the entry is refreshed and aging counter is reset to 0.
If there is no traffic from that FDB entry during this polling interval, the age gets incremented till the configured age time (configured by configure fdb agingtime seconds).The entry gets removed when there is no traffic flow from this FDB entry when the age count reaches the configured age time.
Polling interval = FDB aging time/4 (subject to the minimum and maximum values being 10 and 60 seconds respectively).
Aging is controlled entirely by the hardware based on the traffic hit that happens for the individual FDB entry. The age from show fdb output is alway shown as 0. The entry will be removed when it ages out.
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