This counter tallies CFM frames that arrived with a structure the device could not parse, such as a truncated header, an invalid TLV chain, or a length field that does not match the actual frame size, and discards them as malformed. Because CFM frames only reach this device from directly connected or same-MD-level neighbors, a rising count here almost always points to a cabling or duplex problem, or a buggy CFM implementation on a specific neighboring device, rather than anything wrong with this device's own configuration. Correlating a jump in this counter with the physical port it arrived on is usually enough to isolate which neighbor is sending bad frames.