Information About MAC Addresses
To switch frames between LAN ports, the switch maintains an address table. When the switch receives a frame, it associates the media access control (MAC) address of the sending network device with the LAN port on which it was received.
The switch dynamically builds the address table by using the MAC source address of the frames received. When the switch receives a frame for a MAC destination address not listed in its address table, it floods the frame to all LAN ports of the same VLAN except the port that received the frame. When the destination station replies, the switch adds its relevant MAC source address and port ID to the address table. The switch then forwards subsequent frames to a single LAN port without flooding all LAN ports.
You can also enter a MAC address, which is termed a static MAC address, into the table. These static MAC entries are retained across a reboot of the switch.
Starting with Cisco NX-OS Release 7.2(0)N1(1), the RMAC Learning feature is supported on Cisco Nexus 5600 and 6000 series switches. This feature allows the default MAC address (RMAC) of a VLAN interface to be dynamically learned on another VLAN over a bridged interface on the switch. For example, consider two VLANs—VLAN X and VLAN Y—bridged over an external device. If a customer has a VLAN interface configured on VLAN Y, the MAC address of the interface will be dynamically learned on VLAN X.