MAC Address Withdrawal TLV Support

MAC address withdrawal is a feature that is enabled by default, but you can disable this feature. When this feature is disabled, MAC addresses on a failed pseudowire eventually age out, but it takes the VPLS network longer to adjust than if MAC address withdrawal is enabled. This section describes how this feature operates when it is enabled.

After certain network recovery events, MAC addresses should be unlearned. For example, when an MTU VPLS network facing port goes down, the MTU withdraws the VC FEC label to the PE. The PE, in turn, flushes its FDB of any MAC addresses learned from the MTU and the PE sends an address-withdraw message to all VPLS full-mesh core peer PE nodes. The core peer PE nodes must flush their FDB of any matching unlearned MAC address specified in the address-withdraw messag,e regardless of how the MAC was learned. By withdrawing a MAC address immediately, the PE is forced to flood traffic destined to unlearned MAC addresses specified in the address-withdraw message. If an alternate VPLS path exists, the new path is quickly learned without having to wait for the FDB MAC entry to age out.

The address-withdraw message is sent when a spoke pseudowire terminates to a core VPLS PE node from an MTU. If the MTU has a backup pseudowire, the MTU sends a MAC address-withdrawal message using the now active backup pseudowire to the PE. If the VPLS access is protected using a redundant MTU protection scheme and the backup pseudowire is on the redundant MTU, then the redundant MTU sends a MAC address-withdrawal message using its now active backup pseudowire to the PE.

When a node needs to withdraw a MAC address, it can signal the MAC withdraw using a withdraw message in one of two ways: the MAC address is explicitly specified in a MAC TLV; or an empty MAC TLV is sent indicating that all MAC addresses for the VPLS have been withdrawn. Because this information must be propagated to all VPLS nodes, a control plane processing trade-off exists. To reduce the processing load on the management module, an empty MAC TLV is sent. This forces all peer PE nodes to flush their MAC FDB for the VPLS specified in the FEC TLV. The control module supports the processing of multiple withdraw messages per VPLS, since other vendors may choose not to implement this optimization.