The Network Microscope

Terry Slattery
Principal Architect

I have an occasional need for a network microscope.  You know the situation — someone contacts you with the story that the network is slow.  My vision of a network microscope is something that allows me to see what’s happening on the link.  Doing show interface doesn’t cut it for me because it is one snapshot and it doesn’t tell me what applications and users are using the link.

What I want starts with a rapid snmp poller that plots the collected data in a strip-chart format over time, rather like MRTG, but with a fast polling frequency.  A header that shows the interface configuration settings like IP address, VLAN ID and name, duplex, and speed would be very valuable too.
The poller should be able to show both in and out traffic as well as in and out error types using a stacked plot.  The polling period needs to be adjustable, possibly down to one second intervals.  [Note: Pete Welcher told me that Cisco updates its counters at about a one second interval, so aliasing can occur if polling at one second intervals.]

As I said above, it needs to be a strip-chart type display so I can see historical information.  It would also be useful to see running statistics for the collected data, such as peak, average, 95th percentile, and standard deviation.  This display helps me answer the question “how much” about the link’s utilization and errors.
The next part of the network microscope would show netflow data, which gives me an idea of the type of traffic that is using the link and the systems that are sending and receiving the data.  This data answers the questions of what and who about a slow link.

Tie the two parts together and I would have a tool in which I can click on a traffic burst and see the appropriate netflow data displayed.

The utilization and errors tell me how much, and netflow tells me what applications and who is using them.  If you’re aware of a tool like this, particularly if it is not packaged with an expensive NMS, I’d like to hear about it.

I’m also interested in other diagnostic tools that you find or envision.



Re-posted with Permission 

NetCraftsmen would like to acknowledge Infoblox for their permission to re-post this article which originally appeared in the Applied Infrastructure blog under


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