Cisco Systems WSC4500X16SFP Manual De Usuario
C H A P T E R
35-1
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
35
Port Unicast and Multicast Flood Blocking
This chapter describes how to configure multicast and unicast flood blocking on the Catalyst 4500 series
switch. This chapter contains these topics:
switch. This chapter contains these topics:
•
•
Note
For complete syntax and usage information for the switch commands used in this chapter, refer to the
Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at
Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at
Overview of Flood Blocking
Occasionally, unknown unicast or multicast traffic is flooded to a switch port because a MAC address
has timed out or has not been learned by the switch. (This condition is especially undesirable for a private
VLAN isolated port.) To guarantee that no unicast and multicast traffic is flooded to the port, use the
switchport block unicast and switchport block multicast commands to enable flood blocking on the
switch.
has timed out or has not been learned by the switch. (This condition is especially undesirable for a private
VLAN isolated port.) To guarantee that no unicast and multicast traffic is flooded to the port, use the
switchport block unicast and switchport block multicast commands to enable flood blocking on the
switch.
Note
The flood blocking feature is supported on all switched ports (including PVLAN ports) and is applied
to all VLANs on which the port is forwarding.
to all VLANs on which the port is forwarding.
Configuring Port Blocking
By default, a switch floods packets with unknown destination MAC addresses to all ports. If unknown
unicast and multicast traffic is forwarded to a switch port, there might be security issues. To prevent
forwarding such traffic, you can configure a port to block unknown unicast or multicast packets.
unicast and multicast traffic is forwarded to a switch port, there might be security issues. To prevent
forwarding such traffic, you can configure a port to block unknown unicast or multicast packets.
Note
Blocking of unicast or multicast traffic is not automatically enabled on a switch port; you must
explicitly configure it.
explicitly configure it.