An entry in this table represents detour LSP or bypass tunnel setup constraints for an interface or link to be protected by detour LSPs or a bypass tunnel. Once the LSP or tunnel instance to be protected is identified in the mplsTunnelTable, the corresponding mplsTunnelIfIndex value of that tunnel can be used to get the ifIndex of the underlying physical interface using the ifStackTable. That ifIndex of the underlying physical interface will be used as mplsFrrGeneralConstraintsIfIndexOrZero in this table to protect the LSPs or tunnel instances determined earlier. It is recommended that ifIndex persistence be enabled across re-initializations. If persistence is not implemented, then the value of mplsFrrGeneralConstraintsIfIndexOrZero in this table cannot be guaranteed across restarts and all entries in this table MUST NOT be persistent, or the values of mplsFrrGeneralConstraintsIfIndexOrZero MUST be reconstructed on restart. SNMP engines must only allow entries in this table to be created for tunnel instances that require fast reroute as indicated by the presence of the FAST_REROUTE object in the signaling for the LSP in question. An entry in this table can be created only if a corresponding entry in mplsTunnelTable exists with the same mplsTunnelIndex as mplsFrrGeneralConstraintsTunnelIndex. Entries in this table are deleted when the corresponding entries in mplsTunnelTable are deleted. It is recommended that entries in this table be persistent across reboots. Entries indexed with mplsFrrGeneralConstraintsIfIndexOrZero and set to 0 apply to all interfaces on this device for which the FRR feature can operate. If the mplsTunnelInstance object is set to a value of 0, it indicates that the mplsTunnelEntry contains a tunnel ingress. This is typically how configuration of this feature is performed on devices where the actual protection LSP used is left up to the protecting tunnel. However, in cases where static configuration is possible, any valid tunnel instance is possible; however, it is strongly RECOMMENDED that the instance index SHOULD use the following convention to identify backup LSPs: - lower 16 bits : protected tunnel instance - higher 16 bits: must be all zeros