Operation Manual – MAC Address Table ManagementH3C S5600 Series Ethernet SwitchesChapter 1 MAC Address TableManagement1-44) At this time, the MAC address table of the switch includes two forwarding entriesshown in Figure 1-5. When forwarding the response packet, the switch unicaststhe packet instead of broadcasting it to User A through GigabitEthernet 1/0/1,because MAC-A is already in the MAC address table.Figure 1-5 MAC address table entries of the switch (2)5) After this interaction, the switch directly unicasts the packets destined for User Aand User B based on the corresponding MAC address table entries.Note:z Under some special circumstances, for example, User B is unreachable or User Breceives the packet but does not respond to it, the switch cannot learn the MACaddress of User B. Hence, the switch still broadcasts the packets destined for UserB.z The switch learns only unicast addresses by using the MAC address learningmechanism but directly drops any packet with a broadcast source MAC address.1.1.3 Managing MAC Address TableI. Aging of MAC address tableTo fully utilize a MAC address table, which has a limited capacity, the switch uses anaging mechanism for updating the table. That is, the switch starts an aging timer for anentry when dynamically creating the entry. The switch removes the MAC address entryif no more packets with the MAC address recorded in the entry are received within theaging time.Note:z The MAC address aging timer only takes effect on dynamic MAC address entries.z With the destination MAC address triggered update function enabled, when a switchfinds a packet with a destination address matching one MAC address entry withinthe aging time, it updates the entry and restarts the aging timer.
