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Network Statistics
The best manual way to gather long-term network statistics is to use your analyzer. If you have a lot of segments, you should get an analyzer with a probe system such as Observer, LANalyzer Agent, or the Distributed Sniffer. For our purposes, well pretend that you only have one segment youre interested in getting statistics on.
Lets say that my shops only analyzer is the LANalyzer. A LANalyzer allows you to export trend details to a disk file that you can then import into whatever spreadsheet you like. All I do is start it running on Monday, stop it Monday night, and save the trend data to disk (see Figure 23.4). Then I repeat the same steps on Tuesday, Wednesday, Thursday, and Friday.
Figure 23.4 LANalyzer can show you details or trends.
With LANalyzer, I end up with several vital statistics that are sampled every 15 minutes:
I definitely like to chart the kilobytes per secondthis lets me know how quickly my little data highway is actually flowing. I also chart the utilization. Although this pretty much follows the curve of the KB/sec statistic, it cant hurt, and it reminds me how much of my pipe I have left. I dont usually bother with packets per second, but I definitely chart the errors; this should be a long, flat line at the bottom of the graph with very few peaks.
Baseline Bottom Line
After youve done your baseline homework, when a user reports slowness on the network, its a simple matter to compare values that youre currently getting to what they should be on your baseline graph. This allows you to know whether these stats are out of line for your network. You can then take appropriate action:
Although troubleshooting slowness problems can seem to be a black art, when you break down any network session into its component parts in a variation on the divide-and-conquer theme, it quickly becomes apparent which part is the bottleneck on your information highway.
Your family trip can take a lot longer to complete than you expect due to highway traffic or road conditions. Similarly, your application can move slowly due to a variety of reasonsthe most obvious being network utilization. Other reasons include server slowdown, router or switch latency, and application or protocol efficiency problems.
Baselining your network is an important step in being able to quickly determine which of these reasons is causing your slowdown; if you dont know how things are when life is great, you have no reference to troubleshoot by. With a baseline, you can compare current stats to normal statsjust as a doctor does when diagnosing your blood chemistryand quickly take action to fix it. You can manually take baselines, or you can buy into an SNMP management package that will create the baseline for you. SNMP is certainly the yummier option; however, its possible to do this on the cheap sideits just more of a pain in the neck.
Q Which network analyzers can be used to manually baseline a network segment?
A Just about all the newer ones. The exact technique may vary, but the basic functions for gathering statistics about the segment youre analyzing are the same. Very old DOS-based analyzers might not have the ability to save statistics over a time frame, however. Just ask before you buy.
Q About that latency analysis method: Do the analyzers need to have synchronized clocks?
A No, thats the cool thing about this method. Youre taking the total trip time differences on both ends. Because the difference between the differences has to be the total amount of time the packet spends in the switch or router going both ways, you divide that number by 2 to get the latency for a one-way trip.
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