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Chapter 21
Configuring Port-Based Traffic Control
Configuring Port Blocking
By default, the switch floods packets with unknown destination MAC addresses out of all ports. If
unknown unicast and multicast traffic is forwarded to a protected port, there could be security issues. To
prevent unknown unicast or multicast traffic from being forwarded from one port to another, you can
block a port (protected or nonprotected) from flooding unknown unicast or multicast packets to other
ports.
These sections contain this configuration information:
•
•
Default Port Blocking Configuration
The default is to not block flooding of unknown multicast and unicast traffic out of a port, but to flood
these packets to all ports.
Blocking Flooded Traffic on an Interface
The interface can be a physical interface or an EtherChannel group. When you block multicast or unicast
Note
traffic for a port channel, it is blocked on all ports in the port-channel group.
Beginning in privileged EXEC mode, follow these steps to disable the flooding of multicast and unicast
packets out of an interface:
Command
Step 1
configure terminal
Step 2
interface interface-id
Step 3
no shutdown
Step 4
switchport block multicast
Step 5
switchport block unicast
Step 6
end
Step 7
show interfaces interface-id switchport
Step 8
copy running-config startup-config
To return the interface to the default condition where no traffic is blocked and normal forwarding occurs
on the port, use the no switchport block {multicast | unicast} interface configuration commands.
78-17058-01
Default Port Blocking Configuration, page 21-7
Blocking Flooded Traffic on an Interface, page 21-7
Purpose
Enter global configuration mode.
Specify the interface to be configured, and enter interface
configuration mode.
Enable the port, if necessary. By default, UNIs are disabled, and
NNIs are enabled.
Block unknown multicast forwarding out of the port.
Block unknown unicast forwarding out of the port.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
Configuring Port Blocking
21-7
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