Cisco Catalyst 4500 Series - Blocking Flooded Traffic on an Interface

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Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
OL_28731-01
Chapter 56 Port Unicast and Multicast Flood Blocking
Configuring Port Blocking
Note Blocking of unicast or multicast traffic is not automatically enabled on a switch port; you must explicitly
configure it.
Blocking Flooded Traffic on an Interface
Note The interface can be a physical interface (for example, GigabitEthernet 1/1) or an EtherChannel group
(such as 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.
Note Starting with Cisco IOS Release 12.2(52)SG, only IPV4 and IPv6 unknown multicast traffic flooding is
blocked; Layer 2 unknown multicast flooding is not. This behavior stems from a fix for the following
problem: when you configure blocking of unknown multicast flooding on a port, broadcast traffic to the
port is also blocked.
To disable the flooding of multicast and unicast packets to an interface, perform this task:
This example shows how to block unicast and multicast flooding on a GigabitEthernet interface1/1 and
how to verify the configuration:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface gigabitethernet1/1
Switch(config-if)# switchport block multicast
Switch(config-if)# switchport block unicast
Switch(config-if)# end
Switch# show interface gigabitethernet1/1 switchport
Name: Gi1/3
Switchport: Enabled
Command Purpose
Step 1
Switch# configure terminal
Enters global configuration mode.
Step 2
Switch(config)# interface interface-id
Enters interface configuration mode and enter the type and
number of the switch port interface (for example,
GigabitEthernet 1/1).
Step 3
Switch(config-if)# switchport block
multicast
Blocks unknown multicast forwarding to the port.
Step 4
Switch(config-if)# switchport block unicast
Blocks unknown unicast forwarding to the port.
Step 5
Switch(config)# end
Returns to privileged EXEC mode.
Step 6
Switch#
show interface interface-id
switchport
Verifies your entry.
Step 7
Switch# copy running-config startup-config
(Optional) Saves your entries in the configuration file.