Configuring Port Blocking; Blocking Flooded Traffic On An Interface - Cisco WS-C3550-12G Software Configuration Manual

Configuring Port Blocking

This example shows how to configure Gigabit Ethernet interface 0/3 as a protected port and verify the
configuration:
Switch# configure terminal
Switch(config)# interface gigabitethernet0/3
Switch(config-if)# switchport protected
Switch(config-if)# end
Switch# show interfaces gigabitethernet0/3 switchport
Name: Gi0/3
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
Note
explicitly configure it.

Blocking Flooded Traffic on an Interface

The interface can be a physical interface (for example, GigabitEthernet 0/1) or an EtherChannel
Note
group (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
Step 6
show interfaces interface-id switchport
Step 7 copy running-config startup-config
Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 12
Purpose
Enter global configuration mode.
Enter interface configuration mode, and enter the type and
number of the switchport interface to configure, for example
gigabitethernet0/1.
Block unknown multicast forwarding to the port.
Block unknown unicast forwarding to the port.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Configuring Port-Based Traffic Control
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