1-11 MAC Address Table ConfigurationWhen configuring MAC address tables, go to these sections for information you are interested in:z Overviewz Configuring a MAC Address Tablez Displaying and Maintaining MAC Address Tablez MAC Address Table Configuration ExampleCurrently, interfaces involved in MAC address table configuration can only be Layer 2 Ethernet portsand Layer 2 aggregate interfaces.OverviewEach entry in this table indicates the MAC address of a connected device, to which interface this deviceis connected and to which VLAN the interface belongs. When forwarding a frame, the device first looksup the MAC address table by the destination MAC address of the frame for the outgoing port. If theoutgoing port is found, the frame is forwarded rather than broadcast. Thus, broadcasts are reduced.How a MAC Address Table Entry Is CreatedA MAC address table entry can be dynamically learned or manually configured.Dynamically learning MAC address entriesUsually, a device can populate its MAC address table automatically by learning the source MACaddresses of received frames.The following is how a device learns a MAC address when it receives a frame from a port, Port A forexample:1) Check the source MAC address (MAC-SOURCE for example) of the frame. Assume that frameswith the source MAC address MAC-SOURCE can be forwarded through Port A.2) Look up the MAC address table by the MAC address for a match and do the following:z If an entry is found for the MAC address, update the entry.z If no entry is found, add an entry for the MAC address to indicate from which port the frame isreceived.When receiving a frame destined for MAC-SOURCE, the device looks up the MAC address table andforwards it from Port A.To adapt to network changes, MAC address table entries need to be constantly updated. Eachdynamically learned MAC address table entry has a life time, that is, an aging timer. If an entry has not
