Configuring Unknown Unicast And Multicast Flood Blocking; Understanding Unknown Traffic Flood Control - Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual

Configuring Unknown Unicast and Multicast
Flood Blocking
This chapter describes how to configure the unknown unicast flood blocking (UUFB) and unknown
multicast flood blocking (UMFB) features on the Catalyst 6500 series switches.
For complete syntax and usage information for the commands used in this chapter, refer to the
Note
Catalyst Supervisor Engine 32 PISA Cisco IOS Command Reference, Release 12.2ZY, at this URL:
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2ZY/command/reference/cmdref.h
tml
This chapter contains these sections:
•
•

Understanding Unknown Traffic Flood Control

By default, unknown unicast and multicast traffic is flooded to all Layer 2 ports in a VLAN. You can use
the UUFB and UMFB features to prevent or limit this traffic.
The UUFB and UMFB features block unknown unicast and multicast traffic flooding at a specific port,
only permitting egress traffic with MAC addresses that are known to exist on the port. The UUFB and
UMFB features are supported on all ports that are configured with the switchport command, including
private VLAN (PVLAN) ports.
Entering the switchport block multicast command on nonreceiver (router) ports of the VLAN could
Note
disrupt routing protocols. This command could also disrupt ARP functionality and other protocols, such
as Network Time Protocol (NTP), that make use of local subnetwork multicast control groups in the
224.0.0.0/24 range.
OL-11439-03
Understanding Unknown Traffic Flood Control, page 37-1
Configuring UUFB or UMFB, page 37-2
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
37
C H A P T E R
37-1