Counts input IP datagrams that had no header problems but were still discarded, typically for lack of buffer space, explicitly excluding datagrams lost while awaiting reassembly. A rising ipInDiscards under load is a resource-exhaustion signal distinct from a routing or policy problem; it means the box's IP stack is being overwhelmed faster than buffers can be freed, which on an appliance often correlates with CPU or memory pressure rather than link errors. Example: ipInDiscards climbing during a traffic surge while ifInErrors on the same interface stays at zero points to buffer exhaustion in the IP stack, not a bad cable.