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Configuring the MAC address table
This feature covers only the unicast MAC address table. For information about configuring static multicast
MAC 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.
Overview
To reduce single-destination packet flooding in a switched LAN, an Ethernet device uses a MAC address
table for forwarding frames through unicast instead of broadcast. An MAC address table entry contains
a destination MAC address, the outgoing interface corresponding to the MAC address, and the ID of the
VLAN to which the outgoing interface belongs. When forwarding a single-destination frame, the device
first looks up the MAC address of the frame in the MAC address table for a match. If the switch finds an
entry, it forwards the frame out of the outgoing port in the entry. If the switch does not find an entry, it
floods the frame out of all but the incoming port.
To view MAC address table information, use the
display mac-address
command, as follows:
<Sysname> display mac-address
MAC 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 created
The switch automatically obtains entries in the MAC address table, or you can add them manually.
MAC address learning
The 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 for
MAC-SOURCE, the device finds the MAC-SOURCE entry in the MAC address table and forwards
the frame out of Port A.
The device performs this learning process each time it receives a frame from an unknown source MAC
address, until the MAC address table is fully populated.
