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Understanding Traces - III

Where is the problem? The trace below shows that Average Latency over a 12-hour period jumps from 16ms to 196ms at hop 8 - a UUNET router. But, the problem is actually not in UUNET's network - the problem is that Road Runner doesn't have sufficient bandwidth to the Internet backbone, or has not properly balanced routing to its backbone circuits (hop 7)!

Notice the IP #s for hops 3 to 7 all start with 24.25.225 - they are part of the local Road Runner network; if you see a big jump in latency as soon as you leave the local network (in the case below, hop 8) it's likely the problem isn't 'in the backbone' but that your provider hasn't purchased enough bandwidth: over-subscription!

You'll notice the time-line graph at the bottom of the above Ping Plotter display shows severe latency and packet loss for an extended period of time. This graph is to the final destination - in Boston, MA. The trace originates from my computer in Kona, Hawaii.

Ping Plotter includes superb capability to analyze portions of the trace and individual routers.

Right-click on any of the hops, and you have the option to Display TimeLine Graph. Here, I've added the timeline for hop 8:

Notice the grey area near the beginning of the time-line: this is because for this period, a different router was involved. Ping Plotter tracks and can display routing changes.

By double-clicking any routing change, the display will show all the routing used at different points in time.

You can also zoom in on a particular time period. By right-clicking the graph, you can change the time period, and then you can left-click and drag the time-line to any period you want. This zoomed 60-minute view of 8-9pm shows that the latency to the destination shot way up around 8:40pm, without a similar increase at hop 8.

Compare the above to 6:50 - 7:50pm where the latency to the destination is very similar to the samples at hop 8:

There's even more to come in this section.... So check back soon!

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