User manual

Duplicate MAC Address Support
Page 9-31
If your network supports duplicate MAC addresses, there may be a significant performance
impact due to the following reasons:
•A
MAC address is usually stored only in the CAM of the switching module where its desti-
nation address is located. If duplicate MAC addresses are treated as separate addresses,
then the same MAC address may have to be stored in the CAM of multiple switching
modules, not just the module that originally learned the address.
• Every duplicate
MAC address becomes a CAM table entry, so there will be less room in the
CAM for other entries to be learned. Since up to 32 duplications of a single MAC address
are possible, this CAM can become crowded with these duplicate entries.
You can reduce the impact of a crowded
CAM by configuring the Duplicate MAC Aging Timer
in the syscfg command, which is described in Configuring System Information on page 9-
23. This timer allows you to age out Duplicate MAC CAM entries from devices that are inac-
tive for the time period you specify.
• Extra search time will be required for each lookup of the same
MAC address since it is
treated as a separate entry in the CAM.
In addition to these performance impacts, you will lose the tracking of legitimate station
moves. No traps will be sent for Duplicate
MAC addresses that appear in different Groups.