Overview MAC Address Table

A MAC address entry consists of the MAC address of a terminal, the device port that is connected to the terminal, and the ID of the VLAN to which the port belongs. After a device receives a data packet, it matches the destination MAC address of the packet with the MAC address table entries that are saved in the device so as to locate a packet forwarding port efficiently.

MAC addresses are categorized into two types: dynamic MAC addresses and static MAC addresses. Static MAC addresses are categorized into static forwarding MAC addresses and static filtering MAC addresses.

Dynamic MAC address learning is the basic MAC address learning mode of the devices. Each dynamic MAC address entry has aging time. If no packet whose source MAC address matches a MAC address entry is received by the corresponding VLAN and port, the device deletes the MAC address entry.

The dynamic MAC address learning/forwarding process is as follows:

• When a device receives a packet, it searches the MAC address table of the corresponding VLAN for the MAC address entry that matches the source MAC address of the packet. If no corresponding matching entry is available, the source MAC address of the packet is written into the MAC address table, and the aging time timer of the new MAC address entry is started. If a matching MAC address entry is found, the aging time of the MAC address entry is updated.
• In the corresponding VLAN, the device searches the MAC address table for MAC address entry that matches the destination MAC address of the packet. If no matching entry is available, the packet is flooded to the other ports with the same VLAN ID. If a matching MAC address entry is available, the packet is forwarded through the specified port.

Static filtering MAC addresses are used to isolate devices which are aggressive, preventing the devices from communicating with external devices.

The configuration/forwarding process of static filtering MAC addresses is as follows:

• Static filtering MAC addresses can only be configured by users.
• If the source MAC address or destination MAC address of a packet matches a static filtering MAC address entry in the corresponding VLAN, the packet is discarded.

Static forwarding MAC addresses are used to control the routing principle of packets, and prevent frequent MAC address migration of MAC address entries in the table. MAC address migration means that: A device learns a MAC address from port A, then the device receives packets whose source MAC address is the same as the MAC address from port B, and port B and port A belong to the same VLAN. At this time, the forwarding port saved in the MAC address entry is updated from port A to port B.

The configuration/forwarding process of static forwarding MAC addresses is as follows:

• Static forwarding MAC addresses are configured by users.
• If the destination MAC address of a packet matches a static MAC address entry in the corresponding VLAN, the packet is forwarded through the specified port.

One port can learn the same MAC address from different VLANs, but one MAC address can only be learnt by one port in one VLAN.