Disabling Mac Address Learning On A Vlan - Cisco Catalyst 3750-E Software Configuration Manual

Chapter 7 Administering the Switch
Command
Step 4
show mac address-table static
Step 5 copy running-config startup-config
To disable unicast MAC address filtering, use the no mac address-table static mac-addr vlan vlan-id
global configuration command.
This example shows how to enable unicast MAC address filtering and to configure the switch to drop
packets that have a source or destination address of c2f3.220a.12f4. When a packet is received in
VLAN 4 with this MAC address as its source or destination, the packet is dropped:
Switch(config)# mac

Disabling MAC Address Learning on a VLAN

By default, MAC address learning is enabled on all VLANs on the switch. You can control MAC address
learning on a VLAN to manage the available MAC address table space by controlling which VLANs,
and therefore which ports, can learn MAC addresses. Before you disable MAC address learning, be sure
that you are familiar with the network topology and the switch system configuration. Disabling MAC
address learning on a VLAN could cause flooding in the network.
Follow these guidelines when disabling MAC address learning on a VLAN:
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OL-9775-08
Purpose
Verify your entries.
(Optional) Save your entries in the configuration file.
a
ddress-table static c2f3.220a.12f4 vlan 4 drop
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.
Catalyst 3750-E and 3560-E Switch Software Configuration Guide
Managing the MAC Address Table
7-29