Systems and methods for protecting external memory resources to prevent bandwidth collapse in a network processor. One embodiment is a network processor including an input port configured to receive packets from a source device, on-chip memory configured to store packets in queues, and external memory configured to provide a backing store to the on-chip memory. The network processor also includes a processor configured, in response to determining that the source device is unresponsive to a congestion notification, to reduce a size of one or more queues to prevent packets transferring from the on-chip memory to the external memory.