Operationally disabled is the normal operational state for STP on a SAP in a VPLS that has any of the following conditions:
VPLS state administratively down
SAP state administratively down
SAP state operationally down
If the SAP enters the operationally up state with the STP administratively up and the SAP STP state is up, the SAP transitions to the STP SAP discarding state.
When, during normal operation, the router detects a downstream loop behind a SAP, BPDUs can be received at a very high rate. To recover from this situation, STP transitions the SAP to disabled state for the configured forward-delay duration.