This feature provides the ability to have a node deployed as MTUs (Multi-Tenant Units) to be multi-homed for VPLS to multiple routers deployed as PEs without requiring the use of M-VPLS.
In the configuration example shown in Figure 1, the MTUs have spoke-SDPs to two PE 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.
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 the link failure, PEs failure, and so on), the MTUs immediately switch traffic to the backup spoke and start receiving traffic from the standby spoke. Optional revertive operation (with configurable switch-back delay) is supported. Forced manual switchover is also supported.
To speed up the convergence time during a switchover, MAC flush is configured. The MTUs generate a MAC flush message over the newly unblocked spoke when a spoke change occurs. As a result, the PEs receiving the MAC flush, 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.