packet from User B is sent to Ethernet 1/0/4, the switch records the association between the MACcorresponding port to the MAC address table of the switch.ng diagram (3)address of User B and theFigure 18-4 MAC address learniAt this time, the MAC address table of the switch includes two forwarding entries shown in4) Figure18-5. When forwarding the response packet, the switch unicasts the packet instead ofecause MAC-A is already in the MAC addressof the switch (2)broadcasting it to User A through Ethernet 1/0/1, btable.Figure 18-5 MAC address table entriesPort VLAN IDMAC-addressEthernet1/0/1 1MAC-AEthernet1/0/4 1MAC-B) After this interaction, the switch directly unicasts the packets destined for User A and User B basedrresponding MAC address table entries.5on the coz B is unreachable or User B receives thez The switch learns only unicast addresses by using the MAC address learning mechanism butdirectly drops any packet with a broadcast source MAC address.Under some special circumstances, for example, Userpacket but does not respond to it, the switch cannot learn the MAC address of User B. Hence, theswitch still broadcasts the packets destined for User B.Managing MAC AddrAtimer for an entry when dynamically creatingess Tableging of MAC address tableTo fully utilize a MAC address table, which has a limited capacity, the switch uses an aging mechanismfor updating the table. That is, the switch starts an aging18-3
