Table Of Contents

Unknown Unicast Flood Blocking

Understanding UUFB

Configuring UUFB

Unknown Unicast Flood Blocking

---

This chapter describes how to configure the unknown unicast flood blocking (UUFB) feature on the Catalyst 6500 series switches.

---

Note For complete syntax and usage information for the commands used in this chapter, refer to the Cisco IOS Master Command List, Release 12.2SX at this URL:

http://www.cisco.com/en/US/docs/ios/mcl/122sxmcl/12_2sx_mcl_book.html

---

Understanding UUFB

Unknown unicast traffic is flooded to all Layer 2 ports in a VLAN. You can prevent this behavior by using the UUFB feature. The UUFB feature blocks unknown unicast traffic flooding and only permits egress traffic with MAC addresses that are known to exit on the port. The UUFB feature is supported on all ports that are configured with the switchport command, including private VLAN (PVLAN) ports.

Configuring UUFB

To configure UUFB, perform this task:

	Command	Purpose
Step 1	Router# configure terminal	Enters global configuration mode.
Step 2	Router(config)# interface {{type1  slot/port} | {port-channel number}}	Selects the interface to configure.
Step 3	Router(config-if)# switchport block unicast	Enables UUFB on the port.
Step 4	Router(config-if)# do show interfaces [type1 slot/port] switchport | include unicast	Verifies the configuration.

1 type = ethernet, fastethernet, gigabitethernet, or tengigabitethernet

This example shows how to configure UUFB on Fast Ethernet port 5/12 and how to verify the configuration:

Router# configure terminal 

Router(config)# interface fastethernet 5/12 

Router(config-if)# switchport block unicast 

Router(config-if)# do show interface fastethernet 5/12 switchport | include unicast 

Unknown unicast blocked: enabled