Unknown Unicast and Multicast Flood Control

Note ● For complete syntax and usage information for the commands used in this chapter, see these publications:

http://www.cisco.com/en/US/products/ps9536/prod_command_reference_list.html

  • Cisco IOS Release 12.2SY supports only Ethernet interfaces. Cisco IOS Release 12.2SY does not support any WAN features or commands.

 

Tip For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples and troubleshooting information), see the documents listed on this page:

http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html

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Prerequisites for Unknown Traffic Flood Control

None.

Restrictions for Unknown Traffic Flood Control

  • 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.
  • When unknown unicast flood rate-limiting (UUFRL) is enabled, per-VLAN learning must be enabled on all the Layer 3 routed ports, otherwise, any unicast flooded packet coming into a routed port will also be rate-limited by UUFRL.

Information About 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 unknown unicast flood blocking (UUFB), unknown multicast flood blocking (UMFB), and unknown unicast flood rate-limiting (UUFRL) 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.

The UUFRL feature globally rate limits unknown unicast traffic on all VLANs.

Default Settings for Unknown Traffic Flood Control

None.

How to Configure Unknown Traffic Flood Control

How to Configure UUFB or UMFB

To configure UUFB or UFMB, perform this task:

 

Command
Purpose

Step 1

Router# configure terminal

Enters global configuration mode.

Step 2

Router(config)# interface {{ type slot/port } | { port-channel number }}

Selects the interface to configure.

Step 3

Router(config-if)# switchport

Configures the port for Layer 2 switching.

Step 4

Router(config-if)# switchport block { unicast | multicast }

Enables unknown unicast or multicast flood blocking on the port.

How to Configure UUFRL

To configure UUFRL, perform this task:

 

Command
Purpose

Step 1

Router# configure terminal

Enters global configuration mode.

Step 2

Router(config)# platform rate-limit layer2 unknown { byte | pkt } {[[bytes/second]] |[packets/second]} {[ [no of bytes allowed in each burst] burst [burst-period] | burst [burst-period]] | [ [no of packets allowed in each burst] [ burst [burst-period] | byte [bytes/second] [[no of bytes allowed in each burst] burst [burst-period] | burst [burst-period] ]] | burst [burst-period] | byte [bytes/second] [ [no of bytes allowed in each burst] burst [burst-period]] | burst [burst-period]] } | { leak }

Enables UUFRL globally and configures the byte/pkt Rate.

(optional)- Leak- Leaks 1 Packet per second to CPU

Step 3

Router(config)# exit

Exits configuration mode.

When you configure UUFRL, note the following information:

  • For the  packets/second value:

– The range is 0 through 33,554,431 (entered as 33554431).

– There is no default value.

  • For the  bytes/second value:

– The range is 0 through 4294967295.

– There is no default value.

  • For the  no of bytes allowed in each burst value:

– The range is 0 through 2147483647.

– There is no default value.

  • For the  burst period value:

– The range is 0 through 1048575(in microseconds)

– There is no default value.

  • For the  no of packets allowed in each burst value:

– The range is 0 through 16777215.

– There is no default value.

Configuration Examples for Unknown Traffic Flood Control

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

Router# configure terminal
Router(config)# interface gigabitethernet 5/12
Router(config-if)# switchport
Router(config-if)# switchport block unicast
Router(config-if)# do show interface gigabitethernet 5/12 switchport | include Unknown
Unknown unicast blocked: enabled
 

This example shows how to configure UUFRL with a rate limit of 1000 pps with a burst of 20 packets with a burst period of 10 microseconds:

Router# configure terminal
Router(config)#platform rate-limit layer2 unknown pkt 1000 20 burst 10
Router(config)# exit

Tip For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples and troubleshooting information), see the documents listed on this page:

http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html

Participate in the Technical Documentation Ideas forum