Switchport Block - Cisco Catalyst 2950 Command Reference Manual

switchport block

switchport block
Use the switchport block interface configuration command to prevent forwarding of unknown multicast
or unicast packets. Use the no form of this command to allow forwarding of unknown multicast or
unicast packets.
This command is available only on these switches:
•
•
Syntax Description
multicast
unicast
Defaults Unknown multicast and unicast traffic are not blocked.
Command Modes Interface configuration
Command History Release
12.1(14)EA1
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.
For more information about blocking packets, see the software configuration guide for this release.
Note
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.
Catalyst 2950 and Catalyst 2955 Switch Command Reference
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switchport block {multicast | unicast}
no switchport block {multicast | unicast}
Catalyst 2950 Long-Reach Ethernet (LRE) switches running Cisco IOS Release 12.1(14)EA1
or later
Catalyst 2950G-12-EI, 2950G-24-EI, 2950G-24-EI-DC, 2950G-48-EI, and 2955 switches running
Cisco IOS Release 12.1(19)EA1 or later
Specify that unknown multicast traffic should be blocked.
Specify that unknown unicast traffic should be blocked.
Modification
This command was introduced.
Chapter 2 Catalyst 2950 and 2955 Cisco IOS Commands
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