Basic System Configuration & Debugging
MAC-SOURCE and Port 1 as a new MAC address entry to the MAC address table.
FIgure 28-3 A switch uses a MAC address table to forward packets.
After learning the source address of the packet, the switch searches the MAC address
table for the destination MAC address of the received packet:
If it finds a match, it directly forwards the packet.
If it finds no match, it forwards the packet to all ports, except the receiving port, within the
VLAN to which the receiving port belongs. Normally, this is referred to as broadcasting the
packet.
After the packet is broadcast:
If the network device returns a packet to the switch, this indicates the packet has been sent
to the destination device. The MAC address of the device is carried in the packet. The switch
adds the new MAC address to the MAC address table through address learning. After that,
the switch can directly forward other packets destined for the same network device by using
the newly added MAC address entry.
If the destination device does not respond to the packet, this indicates that the destination
device is unreachable or that the destination device receives the packet but gives no
response. In this case, the switch still cannot learn the MAC address of the destination device.
Therefore, the switch will still broadcast any other packet with this destination MAC address.
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 removes the MAC address entries
related to a network device if no packet is received from the device within the aging time.
Aging time only applies to dynamic MAC address entries.
You can manually configure (add or modify) a static or dynamic MAC address entry based
on the actual network environment.
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