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Cisco ME 3400 EthernetAccess Switch SoftwareConfiguration Guide
78-17058-01
Chapter21 Configuring Port-Based Tra ffic Control Configuring Port Blocking
Configuring Port Blocking
By default, the switch floods packets with unknown destination MAC addresses out of all po rt s. If
unknown unicast and multicast traffic is forwarded to a protec ted port, ther e could b e secur ity issues. To
prevent unknown unicast or multicast traffic from being forwarded from one port to another, you can
block a port (protected or nonprotected) from flooding unknown unicast or multicast packets to other
ports.
These sections contain this configuration information:
•Default Port Blocking Configuration, page 21-7
•Blocking Flooded Traffic on an Interface, page 21-7

Default Port Blocking Configuration

The default is to not block flooding of unknown multicast and unicast traffic out of a port, but to flood
these packets to all ports.

Blocking Flooded Traffic on an Interface

Note The interface can be a physical interface or an EtherChannel group. When you block multicas t or unicast
traffic for a port channel, it is blocked on all ports in the port-channel group.
Beginning in privileged EXEC mode, follow these steps to disable the flooding of mult icast and unicast
packets out of an interface:
To return the interface to the default condition where no traffic is blocke d and normal forwa rding occurs
on the port, use the no switchport block {multicast | unicast} interface configuration commands.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Specify the interface to be configured, and enter interface
configuration mode.
Step3 no shutdown Enable the port, if necessary. By default, UNIs are disabled, and
NNIs are enabled.
Step4 switchport block multicast Block unknown multicast forwarding out of the port.
Step5 switchport block unicast Block unknown unicast forwarding out of the port.
Step6 end Return to privileged EXEC mode.
Step7 show interfaces interface-id switchport Verify your entries.
Step8 copy running-config startup-config (Optional) Save your entries in the configuration file.