Cisco WS-C3560E-48PD-SF Command Reference - Page 656

switchport block Chapter 2 Catalyst 3560 Switch Cisco IOS Commands switchport block Use the switchport block interface configuration command to prevent unknown multicast or unicast packets from being forwarded. Use the no form of this command to allow forwarding unknown multicast or unicast packets. switchport block {multicast | unicast} no switchport block {multicast | unicast} Syntax Description multicast unicast Specify that unknown multicast traffic should be blocked. Specify that unknown unicast traffic should be blocked. Defaults Unknown multicast and unicast traffic is not blocked. Command Modes Interface configuration Command History Release 12.1(19)EA1 Modification This command was introduced. Usage Guidelines By default, all traffic with unknown MAC addresses is sent to all ports. You can block unknown multicast or unicast traffic on protected or nonprotected ports. If unknown multicast or unicast traffic is not blocked on a protected port, there could be security issues. Blocking unknown multicast or unicast traffic is not automatically enabled on protected ports; you must explicitly configure it. For more information about blocking packets, see 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 Command show interfaces switchport Description Displays the administrative and operational status of a switching (nonrouting) port, including port blocking and port protection settings. 2-624 Catalyst 3560 Switch Command Reference 78-16405-05