The ESXi host runs a task that checks the netPktPool memory usage every 5 seconds. When the available memory is below the threshold value the alarm is triggered when the task runs, creating the messages in the hostd.log file and the events displayed in vCenter Server. This continues until the available memory is above the threshold value for the netPktPool. This can appear when there is a burst in network traffic and there are unused buffers in the pool that have not been cleared.