3Com Switch 8800 Configuration Guide Chapter 44 MAC Address Table Management
44-1
Chapter 44 MAC Address Table Management 44.1 MAC Address Table Management Overview
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.