|
Switches learn the MAC addresses of PCs
or workstations that are connected to their switch ports by examining
the source address of frames that are received on that port. These
learned MAC addresses are then recorded in a MAC address table. Frames
having a destination MAC address that has been recorded in the table can
be switched out to the correct interface.
To examine the addresses that a switch has learned, enter the privileged
EXEC command
show mac-address–table.
A switch dynamically learns and maintains
thousands of MAC addresses. To preserve memory and for optimal operation
of the switch, learned entries may be discarded from the MAC address
table. Machines may have been removed from a port, turned off, or moved
to another port on the same switch or a different switch. This could
cause confusion in frame forwarding. For all these reasons, if no frames
are seen with a previously learned address, the MAC address entry is
automatically discarded or aged out after 300 seconds.
Rather than wait for a dynamic entry to
age out, the administrator has the option to use the privileged EXEC
command clear mac-address-table.
 MAC address
entries that an administrator has configured can also be removed using
this command. Using this method to clear table entries ensures that
invalid addresses are removed immediately.
| |
Lab Activity
Lab Exercise: Managing the MAC Address Table
In this lab, the student will create a basic switch
configuration and manage the MAC table.
|
|
|
| |
Lab Activity
e-Lab Activity: Managing the MAC Address Tables
In this lab, the student will observe and clear the MAC
address table.
|
|
|
Web Links