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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter7 Administering the Switch
Managing the MAC Address Table
Follow these guidelines when disabling MAC address learning on a VLAN:
•Use caution before disabling MAC address learning on a VLAN with a configured switch virtual
interface (SVI). The switch then floods all IP packets in the Layer 2 domain.
•You can disable MAC address learning on a single VLAN ID (for example, no mac address-table
learning vlan 223) or on a range of VLAN IDs (for example, no mac address-table learning vlan
1-20, 15).
•We recommend that you disable MAC address learning only in VLANs with two ports. If you
disable MAC address learning on a VLAN with more than two ports, every packet entering the
switch is flooded in that VLAN domain.
•You cannot disable MAC address learning on a VLAN that is used internally by the switch. If the
VLAN ID that you enter is an internal VLAN, the switch generates an error message and rejects the
command. To view internal VLANs in use, enter the show vlan internal usage privileged EXEC
command.
•If you disable MAC address learning on a VLAN configured as a private-VLAN primary VLAN,
MAC addresses are still learned on the secondary VLAN that belongs to the private VLAN and are
then replicated on the primary VLAN. If you disable MAC address learning on the secondary
VLAN, but not the primary VLAN of a private VLAN, MAC address learning occurs on the primary
VLAN and is replicated on the secondary VLAN.
•You cannot disable MAC address learning on an RSPAN VLAN. The configuration is not allowed.
•If you disable MAC address learning on a VLAN that includes a secure port, MAC address learning
is not disabled on that port. If you disable port security, the configured MAC address learning state
is enabled.
Beginning in privileged EXEC mode, follow these steps to disable MAC address learning on a VLAN:
To reenable MAC address learning on a VLAN, use the default mac address-table learning vlan
vlan-id global configuration command. You can also reenable MAC address learning on a VLAN by
entering the mac address-table learning vlan vlan-id global configuration command. The first
(default) command returns to a default condition and therefore does not appear in the output from the
show running-config command. The second command causes the configuration to appear in the show
running-config privileged EXEC command display.
This example shows how to disable MAC address learning on VLAN 200:
Switch(config)# no mac address-table learning vlan 200
You can display the MAC address learning status of all VLANs or a specified VLAN by entering the
show mac-address-table learning [vlan vlan-id] privileged EXEC command.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 no mac address-table learning vlan
vlan-id
Disable MAC address learning on the specified VLAN or VLANs. You
can specify a single VLAN ID or a range of VLAN IDs separated by a
hyphen or comma. Valid VLAN IDs are 1 to 4094.
Step3 end Return to privileged EXEC mode.
Step4 show mac address-table learning [vlan
vlan-id]
Verify the configuration.
Step5 copy running-config startup-config (Optional) Save your entries in the configuration file.