Requirements and Limitations
  
  
    The configuration
      in
      the following figure has the following requirements and limitations:
    
      - The VPLS nodes with STP redundancy (Switches S1 and S2) must
        always be the lowest priority STP bridges to ensure that STP port blocking is done by one of
        the VPLS nodes. For example, the following priorities for the nodes
        in
        the following figure will work correctly: S1, priority 8192; S2, priority
        4096; R1, priority 32768; and R2, priority 32768.
- For VPLS STP redundancy to work properly, the VPLS nodes must be
        directly connected to the STP nodes. For example, if a node R3 is added between S2 and R2,
        node S2 cannot directly detect a failure of the link between R3 and R2.