3com DUA1750-2BAA01 Manual De Usuario

3Com Switch 8800 Configuration Guide 

Chapter 44  MAC Address Table Management

 

44-1 

An Ethernet 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 Ethernet switch 

connected to it. The dynamic entries (not configured manually) are learned by the 

Ethernet switch. The Ethernet 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 Ethernet 

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

directly thereafter.  

 

MAC Address

Port

MACA

1

MACB

1

MACC

2

MACD

2

MACD MACA

......

Port 1

MACD MACA

......

Port 2

 

Figure 44-1 The Ethernet switch forwards packets with MAC address table 

The Ethernet 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.