2.2.1 Backwards Learning contd.
nAs the network changes over time, bridges update adddresses continuously, always check to see if
the entry they have for an address has not changed (busy bees!).
nThey also purge addresses
that have not been checked/ updated in a recent time interval (aging time). Note that each
incoming frame involves 2 routing table lookups: 1)
for the destination address and 2) for the source
address. The latter lookup is either used for adding a
new address or updates the time associated with the
entry for that source, in other words the time field is
constantly being refreshed. Note that a destination
lookup does not refresh the time field!