3com WX3000 Manuel D’Utilisation

 

1-3 

Figure 1-4 MAC address learning diagram (3)  

Geth 1/0/1

Geth 1/0/3

Geth 1/0/4

User A

User B

User C

 

 

4)  At this time, the MAC address table of the device includes two forwarding entries shown in 

. When forwarding the response packet, the device unicasts the 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) 

Port

VLAN ID

MAC-address

GigabitEthernet1/0/1

1

MAC-A

GigabitEthernet1/0/4

1

MAC-B

 

 

5)  After this interaction, the device directly unicasts the communication packets between User A and 

User B based on the corresponding MAC address table entries.  

 

z 

Under some special circumstances, for example, User B is unreachable or User B receives the 

packet but does not respond to it, the device cannot learn the MAC address of User B. Hence, the 

device still broadcasts the packets destined for User B. 

z 

The device learns only unicast addresses by using the MAC address learning mechanism but 

directly drops any packet with a broadcast source MAC address. 

 

To fully utilize a MAC address table, which has a limited capacity, the device uses an aging mechanism 

for updating the table. That is, the device starts an aging timer for an entry when dynamically creating 

the entry, and removes the MAC address entry if no more packets with the MAC address recorded in the 

entry are received within the aging time.