Configuring Port Blocking - Cisco Catalyst 3550 series Software Configuration Manual

Configuring Port Blocking

To disable protected port, use the no switchport protected interface configuration command.
This example shows how to configure Gigabit Ethernet interface 0/1 as a protected port and verify the
configuration:
Switch# configure terminal
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# switchport protected
Switch(config-if)# end
Switch# show interfaces gigabitethernet0/1 switchport
Name: Gi0/1
Switchport: Enabled
<output truncated>
Protected: True
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Configuring Port Blocking
By default, the switch floods packets with unknown destination MAC addresses to all ports. If unknown
unicast and multicast traffic is forwarded to a protected port, there could be security issues.
To prevent unknown unicast or multicast traffic from being forwarded from one port to another, you can
configure a port (protected or nonprotected) to block unknown unicast or multicast packets.
Blocking unicast or multicast traffic is not automatically enabled on protected ports; you must explicitly
Note
configure it.
Blocking Flooded Traffic on an Interface
The interface can be a physical interface (for example, Gigabit Ethernet 0/1) or an EtherChannel group
Note
(for example, port-channel 5). When you block multicast 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 multicast and unicast
packets to an interface:
Command
Step 1
configure terminal
Step 2 interface interface-id
Step 3
switchport block multicast
Step 4 switchport block unicast
Step 5
end
Catalyst 3550 Multilayer Switch Software Configuration Guide
21-6
Chapter 21
Purpose
Enter global configuration mode.
Specify the type and number of the physical interface to
configure, for example gigabitethernet0/1, and enter interface
configuration mode.
Block unknown multicast forwarding to the port.
Block unknown unicast forwarding to the port.
Return to privileged EXEC mode.
Configuring Port-Based Traffic Control
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