• Switchport blocking is supported on all switched ports (including PVLAN ports) and is applied to all
VLANs on which the port is forwarding.
• Switchport blocking is not supported for FEX ports.
• When you block unknown multicast or unicast traffic for a port channel, it is blocked on all ports in the
port-channel group.
• Switchport blocking does not offer levels of control. It prevents the flooding of all unknown egress
multicast or unicast packets on the specified port.
• Switchport blocking drops control packets that originate from the CPU on Cisco Nexus 9500 Series
switches. It does not drop packets on Cisco Nexus 9300 Series switches.
Default Settings for Switchport Blocking
This table lists the default settings for switchport blocking parameters.
Table 39: Default Switchport Blocking Parameters
DefaultParameters
DisabledSwitchport blocking
Configuring Switchport Blocking
By default, the switch floods packets with unknown destination MAC addresses to all ports. To prevent the
forwarding of such traffic, you can configure a port to block unknown multicast or unicast packets.
SUMMARY STEPS
1. configure terminal
2. interface {ethernet slot/port | port-channel number}
3. [no] switchport block {multicast | unicast}
4. (Optional) show interface [ethernet slot/port | port-channel number] switchport
5. (Optional) copy running-config startup-config
DETAILED STEPS
PurposeCommand or Action
Enters global configuration mode.configure terminal
Example:
Step 1
switch# configure terminal
switch(config)#
Enters interface configuration mode.
interface {ethernet slot/port | port-channel number}
Example:
Step 2
Cisco Nexus 9000 Series NX-OS Security Configuration Guide, Release 9.x
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Configuring Switchport Blocking
Default Settings for Switchport Blocking
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