29
MAC Table
This chapter introduces MAC Table.
29.1 Introduction to MAC Table
The MAC table shows how frames are forwarded or filtered across the switch’s ports. It shows what device MAC address, belonging to what VLAN group (if any) is forwarded to which port(s) and whether the MAC address is dynamic (learned by the switch) or static (manually entered in Static MAC Forwarding).
The switch uses the Filtering Database to determine how to forward frames. See the following figure.
1The switch examines a received frame and learns the port on which this source MAC address came.
2The switch checks to see if the frame's destination MAC address matches a source MAC address already learned in the Filtering Database.
•If the switch has already learned the port for this MAC address, then it forwards the frame to that port.
•If the switch has not already learned 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 learned 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.
Figure 115 MAC Table Flowchart
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