Elements and Functions of a MAC Address Table

Elements

A MAC address table contains entries that are identified by a MAC address and a VLAN ID or VSI name. Each entry specifies the outbound interface through which packets with the specified destination MAC address and VLAN ID or VSI are forwarded. If a destination host joins multiple VLANs or VSI names, the host's MAC address corresponds to multiple VLAN IDs or VSI names. Table 1 provides an example of this scenario. In this case, packets with destination MAC address 0011-0022-0034 and VLAN 10 are forwarded through outbound interface GE3/0/1, whereas packets with the same destination MAC address but VLAN 20 are forwarded through outbound interface GE2/0/4.

**Table 1** MAC address entries
MAC Address	VLAN ID/VSI Name	Outbound Interface
0011-0022-0034	10	GE0/0/1
0011-0022-0034	20	GE0/0/2
0011-0022-0035	30	Eth-Trunk20
0011-0022-0035	huawei	GE0/0/3

Functions

A MAC address table is used for unicast forwarding of packets. In Figure 1, when packets sent from PC1 to PC3 reach the switch, the switch searches its MAC address table for the destination MAC address MAC3 and VLAN 10 in the packets to obtain outbound interface Port3. The switch then forwards packets to PC3 through Port3.

Figure 1 Forwarding based on the MAC address table