Port Blocking
When a packet arrives at the switch, the about-face performs a lookup for the destination MAC abode in the MAC
address table to actuate which anchorage it will use to accelerate the packet out to accelerate on. If no access is begin in the
MAC abode table, the about-face will advertisement (flood) alien unicast or multicast cartage out to all the ports in
the aforementioned VLAN (broadcast domain). Forwarding an alien unicast or multicast cartage to a adequate port
could accession aegis issues.
Unknown unicast or multicast cartage can be blocked from actuality forwarded by application the anchorage blocking feature.
To configure anchorage blocking for alien unicast and multicast flooding, use the afterward procedures:
The switchport block multicast interface agreement command to block alien multicast forwarding
to a port
The switchport block unicast interface agreement command to block alien unicast forwarding to a
port
The appearance interfaces {interface} switchport command to validate the anchorage blocking configuration
By default, ports are not configured in blocking mode. Example 4-2 shows how to accredit and verify about-face ports
configured for the anchorage blocking feature.
Example 4-2. Configuring the Anchorage Blocking Feature
Switch(config)# interface Fastethernet0/1
Switch(config-if)# switchport block multicast
Switch(config-if)# switchport block unicast
Switch(config-if)# end
Switch# appearance interfaces FastEthernet 0/1 switchport
Name: Fa0/1
Switchport: Enabled
Administrative Mode: changeless access
...
Protected: true
Unknown unicast blocked: enabled
Unknown multicast blocked: enabled
Appliance trust: none