This feature provides the ability to have a node deployed as MTUs (Multi-Tenant Unit Switches) to be multi-homed for VPLS to multiple routers deployed as PEs without requiring the use of mVPLS.
In the configuration example shown in Figure: H-VPLS with spoke redundancy, the MTUs have spoke-SDPs to two PEs devices. One is designated as the primary and one as the secondary spoke-SDP. This is based on a precedence value associated with each spoke. If the primary and secondary spoke-SDPs have the same precedence value, the spoke-SDP with lower ID functions as the primary SDP.
The secondary spoke is in a blocking state (both on receive and transmit) as long as the primary spoke is available. When the primary spoke becomes unavailable (because of link failure, PEs failure, and so on), the MTU immediately switches traffic to the backup spoke and starts receiving/sending traffic to/from the standby spoke. Optional revertive operation (with configurable switch-back delay) is applicable only when one of the spokes is configured with precedence of primary. If not, this action does not take place. Forced manual switchover is also supported.
To speed up the convergence time during a switchover, MAC flush is configured. The MTUs generates a MAC flush message over the newly unblocked spoke when a spoke change occurs. As a result, the PEs receiving the MAC flush then flush all MACs associated with the impacted VPLS service instance and forward the MAC flush to the other PEs in the VPLS network if propagate-mac-flush is enabled.