This read-only counter, in frames, tallies frames received from the network with the Forward Explicit Congestion Notification bit set, telling the receiving end that the path is congested. Because FECN informs the receiver rather than the sender, a rising count here by itself doesn't slow anything down; it's up to the receiving application or a higher-layer protocol to react, so sustained FECN counts alongside unchanged throughput often indicate an application that simply isn't honoring the congestion signal. A file transfer that keeps running at full speed while this counter climbs steadily suggests the receiving host is ignoring the congestion notification rather than backing off.