3Com 4210 9-Port Configuration Manual page 193

Generally, the majority of MAC address entries are created and maintained through MAC address
learning. The following describes the MAC address learning process of a switch:
1) As shown in Figure
User B, the packet from User A comes into the switch on Ethernet 1/0/1. At this time, the switch
records the source MAC address of the packet, that is, the address MAC-A of User A to the MAC
address table of the switch, forming an entry shown in
Figure 1-1 MAC address learning diagram (1)
Figure 1-2 MAC address table entry of the switch (1)
MAC-address
MAC-A Ethernet1/0/1
2) After learning the MAC address of User A, the switch starts to forward the packet. Because there is
no MAC address and port information of User B in the existing MAC address table, the switch
forwards the packet to all ports except Ethernet 1/0/1 to ensure that User B can receive the packet.
Figure 1-3 MAC address learning diagram (2)
User B
Eth1/0/4 Eth1/0/3
Eth1/0/1
User A
1-1, User A and User B are both in VLAN 1. When User A communicates with
Port VLAN ID
1
User C
1-2
Figure 1-2.