The MAC move feature is useful to protect against undetected loops in a VPLS topology as well as the presence of duplicate MACs in a VPLS service.
If two clients in the VPLS have the same MAC address, the VPLS experiences a high relearn rate for the MAC. When MAC move is enabled, the 7450 ESS, 7750 SR, or 7950 XRS shuts down the SAP or spoke-SDP and creates an alarm event when the threshold is exceeded.
MAC move allows sequential order port blocking. By configuration, some VPLS ports can be configured as ‟non-blockable”, which allows a simple level of control of which ports are being blocked during loop occurrence. There are two sophisticated control mechanisms that allow blocking of ports in a sequential order:
Configuration capabilities to group VPLS ports and to define the order in which they should be blocked
Criteria defining when individual groups should be blocked
For the first control mechanism, configuration CLI is extended by definition of ‟primary” and ‟secondary” ports. Per default, all VPLS ports are considered ‟tertiary” ports unless they are explicitly declared primary or secondary. The order of blocking always follows a strict order starting from tertiary to secondary, and then primary.
The definition of criteria for the second control mechanism is the number of periods during which the specified relearn rate has been exceeded. The mechanism is based on the cumulative factor for every group of ports. Tertiary VPLS ports are blocked if the relearn rate exceeds the configured threshold during one period, while secondary ports are blocked only when relearn rates are exceeded during two consecutive periods, and primary ports when exceeded during three consecutive periods. The retry timeout period must be larger than the period before blocking the highest priority port so that the retry timeout sufficiently spans across the period required to block all ports in sequence. The period before blocking the highest priority port is the cumulative factor of the highest configured port multiplied by 5 seconds (the retry timeout can be configured through the CLI).