Mac Address Table Management; Mac Address Table Management Overview - 3Com 8807 Configuration Manual

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MAC Address Table

A switch maintains a MAC address table for fast forwarding packets. A table entry

includes the MAC address of a device and the port ID of the switch connected to

the device. The dynamic entries (not configured manually) are learned by the

switch. The switch learns a MAC address in the following way: after receiving a

data frame from a port (assumed as port A), the switch analyzes its source MAC

address (assumed as MAC_SOURCE) and considers that the packets destined at

MAC_SOURCE can be forwarded through the port A. If the MAC address table

contains the MAC_SOURCE, the switch will update the corresponding entry;

otherwise, it will add the new MAC address (and the corresponding forwarding

port) as a new entry to the table.

The system forwards the packets whose destination addresses can be found in the

MAC address table directly through the hardware and broadcasts those packets

whose addresses are not contained in the table. The network device will respond

after receiving a broadcast packet and the response contains the MAC address of

the device, which will then be learned and added into the MAC address table by

the switch. The consequent packets destined the same MAC address can be

forwarded directly thereafter.

Figure 21 The switch forwards packets with MAC address table

The switch also provides the function of MAC address aging. If the switch receives

no packet for a period of time, it will delete the related entry from the MAC

address table. However, this function takes no effect on the static MAC addresses.

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