H3C Technologies H3C S12500 Series Switches - Manual (Page 58)

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Configuring the MAC address table
MAC address table configuration applies to Layer 2 Ethernet ports and Layer 2 aggregate interfaces
only.
This document covers only the configuration of static, dynamic, blackhole, and multiport unicast MAC
address table entries. For the configuration of static multicast MAC address table entries, see IP Multicast
Configuration Guide.
Overview
A MAC address table is maintained for frame forwarding. Each entry in this table indicates the following
information:
• The MAC address of a connected network device.
• The interface to which the device is connected.
• The VLAN to which the interface belongs.
When forwarding a frame, the switch first looks up the MAC address table by the destination MAC
address of the frame for the outgoing port. If the outgoing port is found, the frame is forwarded rather
than broadcast, so broadcasts are reduced.
How a MAC address table entry is created
A MAC address table entry can be dynamically learned or manually configured.
Dynamically generate MAC address table entries
Usually, a switch can populate its MAC address table automatically by learning the source MAC
addresses of incoming frames on each port.
When a frame arrives at a port, Port A for example, the switch performs the following tasks:
1. Checks the source MAC address (MAC-SOURCE for example) of the frame.
2. Looks up the source MAC address in the MAC address table.
{
If an entry is found, the switch updates the entry.
{
If no entry is found, the switch adds an entry for MAC-SOURCE and Port A.
3. After learning this source MAC address, when the switch receives a frame destined for
MAC-SOURCE, it finds the MAC-SOURCE entry in the MAC address table and forwards the frame
out of Port A.
The switch performs the learning process each time it receives a frame from an unknown source MAC
address, until the MAC address table is fully populated.
To adapt to network changes, MAC address table entries must be constantly updated. Each dynamically
learned MAC address table entry has an aging timer. If an entry is not updated when the aging timer
expires, it is deleted. If it updates before the aging timer expires, the aging timer restarts.