Switchport Block - Cisco 4500M Command Reference Manual

Chapter2 Cisco IOS Commands for the Catalyst 4500 Series Switches

switchport block

To prevent unknown multicast or unicast packets from being forwarded, use the switchport block
interface configuration command. Use the no form of this command to allow forwarding unknown
multicast or unicast packets.
Syntax Description
multicast
unicast
Defaults
Unknown multicast and unicast traffic are not blocked.
All traffic with unknown MAC addresses is sent to all ports.
Command Modes
Interface configuration
Command History Release
12.1(19)EW
Usage Guidelines
You can block unknown multicast or unicast traffic on switch ports.
Blocking unknown multicast or unicast traffic is not automatically enabled on switch ports; you must
explicitly configure it.
Note
For more information about blocking packets, refer to the software configuration guide for this release.
Examples
This example shows how to block unknown multicast traffic on an interface:
Switch(config-if)# switchport block multicast
You can verify your setting by entering the show interfaces interface-id switchport privileged EXEC
command.
Related Commands
show interfaces switchport
78-16201-01
switchport block {multicast | unicast}
no switchport block {multicast | unicast}
Specifies that unknown multicast traffic should be blocked.
Specifies that unknown unicast traffic should be blocked.
Modification
Support for this command was introduced on the Catalyst 4500 series switch.
Catalyst4500 Series SwitchCiscoIOS Command Reference—Release 12.2(18)EW
switchport block
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