3Com LinkBuilder MSH User Manual page 29

Bridging 1-15
The bridge performs ageing on address list entries. If a port has
not received a packet from a device within a configured time (the
ageing time), the device's address will be removed from the port's
address list. This helps the bridge to efficiently remember devices
that communicate frequently without having to cope with devices
that communicate infrequently or are no longer there.
Because the bridge continually learns new addresses and ages out
old addresses, it does not have to be reconfigured or initialized
when a device is added to the network.
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