Sunday, March 30, 2008

Network and Protocol Analyzers Part 1

The first level of network testing consists of making sure that the underlying physical cabling structure is performing as expected. The next level is to monitor and test the network traffic and messages generated by the network protocols to be sure that you have a healthy network. Network analyzer products operate by monitoring the network at the Data Link and Transport layers in the OSI reference model.

Again, you will find that the tools you can select for protocol analyzers range from the very inexpensive (free) to the very expensive (several thousand dollars). One difference between these kinds of tools and those used to check cables, however, is that you need to have a good understanding of the network structure and protocols used before you can make meaningful judgments about the data you collect. The LAN analyzer allows you to intercept network traffic as it passes through the wire in real- time and save the data for analysis. A good analyzer should be able to produce meaningful statistics about the traffic on the network, decode the protocols that are used, and provide a good filtering capability so that you don't get bogged down in an overwhelming amount of data.

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You should consider many factors when deciding on a network analyzer product. The most basic factor is whether you want a portable device that can be transported to different sites or one or more devices that can be placed at strategic locations in the network to perform continuous monitoring. Other features to consider include the following:

  • Price—Of course, this is always a factor when purchasing equipment for a network.
  • Software or hardware—Do you need a dedicated hardware instrument that can perform intense analysis and connect to multiple segments, or can you live with a software implementation that runs on an existing network workstation?
  • Network interface—Do you need to connect to just a 100BASE-T (or even higher bandwidth devices) environment, or do you need a device that connects to other topologies such as FDDI or Token-Ring?
  • Protocol stack support—Is your network homogeneous, or does it support multiple network protocols?
  • StatisticsWhat kind of statistical data does the instrument support? The most basic is frames-per-second. Others include utilization and usage. Utilization is a measurement of the actual amount of bandwidth that your network media is supporting at any point in time. Usage statistics can tell you what is using that bandwidth—from protocol statistics to such things as the number of collisions on a shared Ethernet segment.
  • Memory and buffers—Does the instrument provide enough buffering capacity to capture frames on a high-speed network such as 100BASE-T? How about Gigabit Ethernet?
  • Filters—Does the analyzer provide sufficient filtering capabilities to allow you to look through large volumes of data to get to the frames that really matter?
  • Import and export—Does the device allow you to save files to a disk or another medium so that you can transfer them to other workstations for further analysis?

A good LAN analyzer allows you to monitor network traffic in real-time mode, using filters to narrow the scope of your view. You can set up capture filters, store part or all of the frames that match in a buffer, and perform further analysis.

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