MAC Limiting

This document describes how to configure MAC limiting.

Restrictions and Usage Guidelines

MAC limiting is supported on the following interface types:

  • You can apply MAC limiting only to bridge-domains.
  • MAC limiting is supported for dynamic MAC addresses.

Configuring MAC Limiting

Mac address limiting per bridge-domain restricts the number of MAC addresses that the router learns in bridge-domain on an EFP, pseudowire or switchport.


Note
Local connect feature is not supported on the Cisco router. However, to simulate a local connect scenario, configure the connecting EFPs on the same bridge domain and disable the mac-learning on the bridge domain by setting the MAC limit to 0. Use the mac-address-table limit bdomain num maximum 0 action limit command to disable mac-learning on the router.

When the total number of addresses in a bridge-domain exceeds the maximum number, the router takes a violation action. You can enable the following actions:

  • Warning—The router sends a syslog message and takes no further action. The router continues learning new MAC addresses and forwarding traffic.
  • Limit—The router sends a syslog message and generates a trap; MAC learning is disabled on the bridge-domain until the recovery mechanism activates. Flooding of frames with new MAC addresses continues; to disable flooding, use the flood keyword. Flooding continues once the total number of MAC entries drops below the threshold value. This option applies only when you configure the limit keyword.

Note
The threshold value must be 80% of the maximum value configured for the recovery mechanism.
  • Shutdown—If the number of addresses exceeds the maximum (MAX) value, the router sends a syslog message and moves the bridge-domain (bdomain) to a disabled state. To restore the bridge-domain, disable and re-enable the mac-limiting feature.

Note
Warning is the default action when no action is configured.

Note

The functionality of automatic error recovery is not supported on the Cisco ASR 900 RSP2 module.

Before you begin

SUMMARY STEPS

  1. configure terminal
  2. mac-address-table limit bdomain id maximum num action {warning | limit | shutdown} [flood]
  3. end
  4. show mac-address-table limit [bdomain id]
  5. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

mac-address-table limit bdomain id maximum num action {warning | limit | shutdown} [flood]

Sets the specific limit and any optional actions to be imposed at the bridge-domain level.

The default maximum value is 500.

Step 3

end

Return to privileged EXEC mode.

Step 4

show mac-address-table limit [bdomain id]

Displays the information about the MAC-address table.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

Example of Enabling Per-Bridge-Domain MAC Limiting

This example shows how to enable per-bridge-domain MAC limiting. 

  • Router# enable
Router# configure terminal
Router(config)# mac-address-table limit bdomain 10 maximum 100 action limit flood
Router(config)# end

Router#show mac-address-table limit bdomain 10
  bdomain       action      flood       maximum     Total entries     Current state
-------------+----------+------------+------------+---------------+---------------
   10           limit      Disable        100            0             Within Limit