Switchport Block - Cisco Catalyst 3750 Command Reference Manual

switchport block

switchport block
Use the switchport block interface configuration command on the switch stack or on a standalone switch
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
multicast
unicast
Defaults Unknown multicast and unicast traffic is not blocked.
Command Modes
Interface configuration
Command History Release
12.1(11)AX
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.
Note 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
Catalyst 3750 Switch Command Reference
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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.
switchport
Description
Displays the administrative and operational status of a switching
(nonrouting) port, including port blocking and port protection settings.
Chapter 2 Catalyst 3750 Switch Cisco IOS Commands
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