A communication interface device, system, method, and design structure for bit shadowing in a memory system are provided. The communication interface device includes shadow selection logic to select a driver bit position as a shadowed driver value, and line drivers to transmit data for the selected driver bit position and the shadowed driver value on separate link segments of a bus. The communication interface device also includes shadow compare logic to compare a selected received value with a shadowed received value from the bus and identify a miscompare in response to a mismatch of the compare, and shadow counters to count a rate of the miscompare relative to a bus error rate over a period of time. A defective link segment is identified in response to the rate of the miscompare within a predefined threshold of the bus error rate.