This counter tallies an internal firmware error condition, a specific subset of the broader inDiscards count, where the IP stack could not allocate a data structure it needed while processing an incoming packet. A nonzero value here points at an internal resource problem within the firmware's IP processing rather than anything wrong on the network. An admin seeing inDataNotAllocated increment would check freeHeap and noMemoryAvailable, since this error likely stems from memory pressure inside the device.