Switchport Block - Cisco Catalyst 3650 series Command Reference Manual

switchport block

switchport block
To prevent unknown multicast or unicast packets from being forwarded, use the switchport block command
in interface configuration mode. To allow forwarding unknown multicast or unicast packets, use the no form
of this command.
switchport block {multicast| unicast}
no switchport block {multicast| unicast}
Syntax Description
multicast
unicast
Command Default
Unknown multicast and unicast traffic is not blocked.
Command Modes
Interface configuration
Command History
Release
Cisco IOS XE 3.3SE
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 unicast traffic on an interface:
Device(config-if)# switchport block unicast
You can verify your setting by entering the show interfaces interface-id switchport privileged EXEC
command.
Command Reference, Cisco IOS XE Everest 16.5.1a (Catalyst 3650 Switches)
130
Specifies that unknown multicast traffic should be blocked.
Only pure Layer 2 multicast traffic is blocked. Multicast packets that contain
Note
IPv4 or IPv6 information in the header are not blocked.
Specifies that unknown unicast traffic should be blocked.
Modification
This command was introduced.