This feature can be used to provide redundant connectivity to a VPRN or IES from a PE providing a VLL service, as shown in Figure: Active/standby VRF using resilient Layer 2 circuits, using either Epipe or Ipipe spoke-SDPs. This feature is supported on the 7450 ESS and 7750 SR only.
In Figure: Active/standby VRF using resilient Layer 2 circuits, PE1 terminates two spoke SDPs that are bound to one SAP connected to CE1. PE1 chooses to forward traffic on one of the spoke SDPs (the active spoke-SDP), while blocking traffic on the other spoke SDP (the standby spoke SDP) in the transmit direction. PE2 and PE3 take any spoke SDPs for which PW forwarding standby has been signaled by PE1 to an operationally down state.
The 7450 ESS, 7750 SR, and 7950 XRS routers are expected to fulfill both functions (VLL and VPRN/IES PE), while the 7705 SAR must be able to fulfill the VLL PE function. Figure: Spoke SDP redundancy model illustrates the model for spoke SDP redundancy into a VPRN or IES.
