This read-only field reports the protocol-specific connection identifier (VLAN ID, DLCI, or packed VPI/VCI depending on the endpoint's protocol) of the specific circuit endpoint where the failure occurred, mirroring the encoding used in circuitSrcConnectionID/circuitDestConnectionID. This lets an admin confirm exactly which logical circuit path failed on a shared physical port that might be carrying several circuits with different connection IDs simultaneously. For example, if a port carries multiple Frame Relay DLCIs, this field distinguishes a failure on DLCI 200 from a failure on DLCI 300 riding the same physical interface.