Mac Address Table Management; Overview - 3Com Switch 4500 26-Port Configuration Manual

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Overview

MAC Address Table
Management
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
it. 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 via 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 for the same MAC address can be
forwarded directly thereafter.
Figure 65 The Switch Forwards Packets with MAC Address Table
MACD MACA
Port 1
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.
MAC Address
MACA
MACB
MACC
......
MACD
MACD MACA
Port 2
Port
1
1
2
2
......