Chapter 11
  |  Interface Commands
Interface Configuration
–  396  –
Related Commands 
negotiation (393)
capabilities (388)
switchport block This command prevents the flooding of broadcast, unknown multicast, or 
unknown unicast packets onto an interface. Use the no form to restore the default 
setting.
Syntax 
[no] switchport block {broadcast | multicast | unicast}
broadcast - Specifies broadcast packets.
multicast - Specifies unknown multicast packets.
unicast - Specifies unknown unicast packets.
Command Mode 
Interface Configuration (Ethernet, Port Channel)
Default Setting 
Disabled 
Command Usage 
By default, broadcast, unknown multicast, and unknown unicast traffic is flooded to 
all ports. This occurs if a MAC address has been timed out or not yet learned by the 
switch. 
Example 
The following example blocks unknown multicast traffic on port 5: 
Console(config)#interface ethernet 1/5
Console(config-if)#switchport switchport block multicast
Console(config-if)#