In one embodiment, an aggregation device operating in a computer network may have a down maintenance end point (MEP) configured on certain of its user-to-network interface (UNI) ports. These down MEPs may then receive continuity check messages (CCMs) from down MEPs configured on customer edge (CE) devices, where each CCM has a media access control (MAC) address of a corresponding CE device UNI port from which the CCM is transmitted. In response to detecting conflicting MAC addresses between CE device UNI ports based on the CCMs, the aggregation device may notify the CE devices corresponding to the conflicting MAC addresses of the conflict.