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5.2.
MAC Management
Dynamic Address
The MAC addresses are learnt by the switch. When the switch receives frames, it will
record the source MAC, the received port and the VLAN in the address table with an age
time. When the age time is expired, the address entry will be removed from the address
table.
Static Address
The MAC addresses are configured by users. The static addresses will not be aged out by
the switch. The static address can be removed by user only.
The maximum static address entry is up to 256.
The switch supports up to 16K address table. The static address and the dynamic address
share the same table.
The
MAC Table
(a MAC table is also known as a filtering database) shows how frames
are forwarded or filtered across the Switch’s ports. When a device (which may belong to a
VLAN group) sends a packet which is forwarded to a port on the Switch, the MAC address
of the device is shown on the Switch’s MAC Table. It also shows whether the MAC address
is dynamic (learned by the Switch) or static (manually entered).
The Switch uses the
MAC Table
to determine how to forward frames. See the following
figure.
1.
The Switch examines a received frame and learns the port from which this source
MAC address came.
2.
The Switch checks to see if the frame's destination MAC address matches a source
MAC address already learnt in the
MAC Table
.
If the Switch has already learnt the port for this MAC address, then it
forwards the frame to that port.
If the Switch has not already learnt the port for this MAC address, then the
frame is flooded to all ports. Too much port flooding leads to network
congestion.
If the Switch has already learnt the port for this MAC address, but the
destination port is the same as the port it came in on, then it filters the frame.