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MAC address configuration
NOTE:
• MAC address configurations related to interfaces apply only to Layer 2 Ethernet interfaces.
• This chapter covers only the management of static and dynamic MAC address entries, not multicast
MAC address entries.
A device maintains a MAC address table for frame forwarding. Each entry in this table indicates the
MAC address of a connected device, to which interface this device is connected and to which VLAN the
interface belongs. A MAC address table consists of two types of entries: static and dynamic. Static
entries are manually configured and never age out. Dynamic entries can be manually configured or
dynamically learned and will age out.
When a frame arrives at a port, Port A for example, the device performs the following tasks:
1. Checks the frame for the source MAC address (MAC-SOURCE for example).
2. Looks up the MAC address in the MAC address table.
î™» If an entry is found, updates the entry.
î™» If no entry is found, adds an entry for the MAC address and the receiving port (Port A) to the
MAC address table.
When receiving a frame destined for MAC-SOURCE, the device looks up the MAC address table and
forwards it from port A.
NOTE:
Dynamically learned MAC addresses cannot overwrite static MAC address entries, but the latter can
overwrite the former.
When forwarding a frame, the device adopts the following forwarding modes based on the MAC
address table:
• Unicast mode: If an entry matching the destination MAC address exists, the device forwards the
frame directly from the sending port recorded in the entry.
• Broadcast mode: If the device receives a frame with the destination address being all Fs, or no entry
matches the destination MAC address, the device broadcasts the frame to all the ports except the
receiving port.