When BGP AD is used for LDP VPLS and LDP is used as the transport tunnel there is no requirement to manually create an SDP. The LDP SDP can be automatically instantiated using the information advertised by BGP AD. This simplifies the configuration on the service node.
Enabling LDP on the IP interfaces connecting all nodes between the ingress and the egress, builds transport tunnels based on the best IGP path. LDP bindings are automatically built and stored in the hardware. These entries contain an MPLS label pointing to the best next hop along the best path toward the destination.
When two endpoints need to connect and no SDP exists, a new SDP is automatically constructed. New services added between two endpoints that already have an automatically created SDP are immediately used. No new SDP is constructed. The far-end information is gleaned from the BGP next hop information in the NLRI. When services are withdrawn with a BGP_Unreach_NLRI, the automatically established SDP remains up as long as at least one service is connected between those endpoints. An automatically created SDP is removed and the resources released when the only or last service is removed.