3Com Switch 7750 Configuration Guide Guide

212 CHAPTER 27: MAC ADDRESS TABLE MANAGEMENT
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CAUTION: For a MAC address entry to be added, the port specified by the
interface keyword must belong to the VLAN specified by the vlan keyword in the
command. Otherwise, the entry will not be added.
Setting the Aging Time
for MAC Address Entries
Setting aging time properly helps implement effective MAC address aging. The
aging time that is too long or too short results in a large amount of broadcast
packets wandering across the network and decreases the performance of the
switch.
■ If the aging time is too long, excessive invalid MAC address entries maintained
by the switch may fill up the MAC address table. This prevents the MAC
address table from varying with network changes in time.
■ If the aging time is too short, the switch may remove valid MAC address
entries. This decreases the forwarding performance of the switch.
This command is used in system view and applies to all ports. Aging applies to only
dynamic MAC addresses that are learnt or configured to age.
Normally, you are recommended to use the default aging time, namely, 300
seconds. The no-aging keyword specifies that MAC address entries do not age
out.
Setting the Maximum
Number of MAC
Addresses a Port Can
Learn
The MAC address learning mechanism enables an Ethernet switch to acquire the
MAC addresses of the network devices on the segment connected to the ports of
the switch. The switch directly forwards the packets destined for these MAC
addresses. An oversized MAC address table may decrease the forwarding
performance of the switch.
By setting the maximum number of MAC addresses that can be learnt from
individual ports, you can control the number of the MAC address entries the MAC
address table can dynamically maintains. If you have set the maximum number of
MAC addresses that a port can learn to count, the port stops learning MAC
addresses when the number of MAC addresses learned by the port reaches count.
Tabl e 137 Add a MAC address entry
Operation Command Description
Enter system view system-view -
Add a MAC address entry
mac-address { static |
dynamic } mac-address
interface interface-type
interface-number vlan vlan-id
Required
Tabl e 138 Set aging time for MAC address entries
Operation Command Description
Enter system view system-view -
Set the aging time of MAC
address entries
mac-address timer { aging
age | no-aging }
Required
The default aging time is 300
seconds.