Switchport Block - Cisco Catalyst 2960 Command Reference Manual

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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.

Syntax Description

Unknown multicast and unicast traffic is not blocked.

Command Modes

Interface configuration

Command History

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.

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

Related Commands

show interfaces

Catalyst 2960 Switch Command Reference

switchport block {multicast | unicast}

no switchport block {multicast | unicast}

Specify that unknown multicast traffic should be blocked.

Specify that unknown unicast traffic should be blocked.

Modification

This command was introduced.

Displays the administrative and operational status of a switching port,

including port blocking and port protection settings.

Chapter 2 Catalyst 2960 Switch Cisco IOS Commands