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Catalyst 3750 Switch Command Reference
OL-8552-07
Chapter 2 Catalyst 3750 Switch Cisco IOS Commands
switchport block
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
Defaults
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.
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
multicast
Specify that unknown multicast traffic should be blocked.
unicast
Specify that unknown unicast traffic should be blocked.
Release
Modification
12.1(11)AX
This command was introduced.
Command
Description
switchport
Displays the administrative and operational status of a switching
(nonrouting) port, including port blocking and port protection settings.
