MAC address limiting per bridge-domain restricts the number of MAC addresses that the router learns in a bridge-domain on an EFP or trunk EFP to a specified number.

Note

For the RSP1 and RSP2 modules, the 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 bridge-domain.

When the total number of MAC addresses (dynamic MAC addresses) in a bridge-domain exceeds the maximum number, then the router takes a violation action. The router either restricts further learning on bridge-domain by itself with a syslog or just intimate the user through a syslog to take further action.

You can enable the following actions when violation occurs:

• Warning—The violation is logged as a syslog message and no further action is taken. There is one syslog message received, when the MAC count exceeds the configured limit (exceed notification) and no more syslog messages are received for the bridge-domain (bdomain) unless the violation is no longer valid (drop notification). When you select the warning action, the further learning of new MAC addresses and forwarding of traffic continue to happen irrespective of violation.

• Limit—When the Limit option is selected as an action for violation, the MAC learning on the bdomain is disabled when violation occurs. No new MAC addresses are learnt on the bdomain until the recovery mechanism gets started. Even though new MAC addresses are not learned but frames are still flooded in the system. If user needs to stop flooding, then a sub action flood can also be used along with limit action.

  Note	The threshold value must be 80% of the maximum value configured for the recovery mechanism.

• Flood—The flood sub action allows the user to disable unknown unicast flooding on a given bdomain. This flood sub action is initiated only when the limit action is configured and violation has occurred. Unknown unicast flooding is disabled only for the interval necessary to limit the entries. Using this option, improves the performance and the flooding is re-enabled when the total number of MAC entries are dropped below the threshold value.

• Shutdown—When the shutdown action is selected, a syslog message is generated and the particular bdomain on which violation occurred is disabled. Hence, all the learning and forwarding of traffic are stopped on the bdomain. The bdomain remain in such state until the feature is explicitly disabled through CLI.

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.

For the limit and warning actions, the recovery mechanism is initiated when the total MAC limit count drops to equal or below a threshold value. The threshold value is dependent on the maximum limit configured on bridge domain (the threshold value is 80% of the limit value). The recovery mechanism reverts the action taken during violation. For example, if the MAC address learning is disabled as a violation action, then it will be re-enabled.

If no maximum value or action option in specified through the mac address-table limit bdomain id maximum num action command, then the default action (warning) and a default maximum value of 500 is configured.

Note	For a MAC limit of 0 with the action limit, limit flood, the violation action occurs when the user configures it irrespective of MAC address learning on the bridge domain. The recovery mechanism is to disable the feature through the no mac address-table limit bdomain id command.