3Com 4500 PWR 26-Port Configuration Manual page 219

packet from User B is sent to Ethernet 1/0/4, the switch records the association between the MAC
address of User B and the
Figure 18-4 MAC address learni
4) At this time, the MAC address table of the switch includes two forwarding entries shown in
18-5. When forwarding the response packet, the switch unicasts the packet instead of
broadcasting it to User A through Ethernet 1/0/1, b
table.
Figure 18-5 MAC address table entries
MAC-address
MAC-A
MAC-B
5 ) After this interaction, the switch directly unicasts the packets destined for User A and User B based
on the co rresponding MAC address table entries.
Under some special circumstances, for example, User
packet but does not respond to it, the switch cannot learn the MAC address of User B. Hence, the
switch still broadcasts the packets destined for User B.
The switch learns only unicast addresses by using the MAC address learning mechanism but
directly drops any packet with a broadcast source MAC address.
Managing MAC Addr
A ging of MAC address table
To fully utilize a MAC address table, which has a limited capacity, the switch uses an aging mechanism
for updating the table. That is, the switch starts an aging
corresponding port to the MAC address table of the switch.
ng diagram (3)
of the switch (2)
Port VLAN ID
Ethernet1/0/1 1
Ethernet1/0/4 1
ess Table
ecause MAC-A is already in the MAC address
B is unreachable or User B receives the
timer for an entry when dynamically creating
18-3
Figure