This command only had to be run once. Interpreting MRTG MRTG graphs show the max output for the time periods displayed. Time is in military time. As a quick reminder, if the time is 13 to 23 subtract 12 from that number to get the standard time. Each line on the y-axis represents one hour.
High spikes indicate a large amount of traffic being sent or received.
The example above shows a high traffic spike. Notice how it distorts the normal looking traffic just above the x-axis. Though accurate it is difficult to see those results. That is why we are using multiple monitoring utilities. The daily chart on MRTG shows a two-day period so the graph will return back to normal after that time.