Cisco Catalyst 3550

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Catalyst 3550 Multilayer Switch Command Reference
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Chapter 2 Catalyst 3550 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 return to the default setting.
switchport block {multicast | unicast}
no switchport block {multicast | unicast}
Syntax Description
Defaults Unknown multicast and unicast traffic are 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 non-protected 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
multicast Specify that unknown multicast traffic should be blocked.
unicast Specify that unknown unicast traffic should be blocked.
Release Modification
12.1(4)EA1 This command was introduced.
Command Description
show interfaces switchport Displays the administrative and operational status of a switching
(nonrouting) port, including port blocking and port protection settings.