Switchport Block - Cisco Catalyst 3750 Metro Command Reference Manual

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.
Syntax Description
multicast
unicast
Defaults Unknown multicast and unicast traffic is not blocked.
Command Modes Interface configuration
Command History Release
12.1(14)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.
With multicast traffic, the port blocking feature blocks only pure Layer 2 packets. Multicast packets that
contain IPv4 or IPv6 information in the header are not blocked.
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.
Catalyst 3750 Metro Switch Command Reference
2-704
switchport block {multicast | unicast}
no switchport block {multicast | unicast}
Specify that unknown multicast traffic should be blocked.
Note
Specify that unknown unicast traffic should be blocked.
Modification
This command was introduced.
Chapter 2 Catalyst 3750 Metro Switch Cisco IOS Commands
Only pure Layer 2 multicast traffic is blocked. Multicast packets that
contain IPv4 or IPv6 information in the header are not blocked.
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