22Configuring the MAC address tableThis feature covers only the unicast MAC address table. For information about configuring static multicastMAC address table entries for IGMP snooping and MLD snooping, see IP Multicast Configuration Guide.The MAC address table can contain only Layer 2 Ethernet ports and Layer 2 aggregate interfaces.The MAC address table configuration tasks are all optional can be performed in any order.OverviewTo reduce single-destination packet flooding in a switched LAN, an Ethernet device uses a MAC addresstable for forwarding frames through unicast instead of broadcast. An MAC address table entry containsa destination MAC address, the outgoing interface corresponding to the MAC address, and the ID of theVLAN to which the outgoing interface belongs. When forwarding a single-destination frame, the devicefirst looks up the MAC address of the frame in the MAC address table for a match. If the switch finds anentry, it forwards the frame out of the outgoing port in the entry. If the switch does not find an entry, itfloods the frame out of all but the incoming port.To view MAC address table information, use the display mac-address command, as follows: display mac-addressMAC ADDR VLAN ID STATE PORT INDEX AGING TIME(s)000f-e201-0101 1 Learned Ethernet1/0/1 AGING--- 1 mac address(es) found ---How a MAC address table entry is createdThe switch automatically obtains entries in the MAC address table, or you can add them manually.MAC address learningThe device can automatically populate its MAC address table by obtaining the source MAC addresses(called "MAC address learning") of incoming frames on each port.When a frame arrives at a port, Port A, for example, the device performs the following tasks:1. Verifies the source MAC address (for example, MAC-SOURCE) of the frame.2. Looks up the source MAC address in the MAC address table.{ If an entry is found, the device updates the entry.{ If no entry is found, the device adds an entry for MAC-SOURCE and Port A.3. After obtaining this source MAC address, when the device receives a frame destined forMAC-SOURCE, the device finds the MAC-SOURCE entry in the MAC address table and forwardsthe frame out of Port A.The device performs this learning process each time it receives a frame from an unknown source MACaddress, until the MAC address table is fully populated.
