Unknown Unicast And Multicast Flood Blocking; Understanding Uufb Or Umfb - Cisco 7604 Configuration Manual

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 Cisco 7600 series routers.
For complete syntax and usage information for the commands used in this chapter, refer to the Cisco IOS
Note
Master Command List, Release 12.2SX at this URL:
http://www.cisco.com/en/US/docs/ios/mcl/122sxmcl/12_2sx_mcl_book.html
Tip For additional information (including configuration examples and troubleshooting information), see the
documents listed on this page:
http://www.cisco.com/en/US/products/hw/routers/ps368/tsd_products_support_series_home.html

Understanding UUFB or UMFB

By default, unknown unicast and multicast traffic is flooded to all Layer 2 ports in a VLAN. You can
prevent this behavior by using 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.
Note Entering the switchport block multicast command on nonreceiver (router) ports of the VLAN could
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.
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