When there are problems on a network, one sure way to narrow them down is through sniffing and testing the network. There are several testers on the market that perform various functions and provide the network manager with data to help diagnose problems. In today's article, we will look at some of the most common types of testers and also take a peak at some resources that should help you determine if your tester or sniffer is up to snuff.
The first step with any testing mechanism is to decide what you wish to test. It is not uncommon for one type of test to lead to another type of test and tester.
Take the following instance: Company A has intermittent network problems where connections drop sporadically.
The first thing the network manager does is open a sniffer. A sniffer will allow the network manager to view traffic packet contents as they move across the network. This will allow him to view error packets as well. This would include errors such as host not available, timeout packets, etc. But how much of this information is "actionable" will depend on what information you glean from viewing the traffic. Some go a step further and will allow you to see speed reports, network utilization, etc. If the communication channel is over-utilized, this may lead you to several other steps including testing the NIC card, testing the switch and switch ports, testing the physical channel, etc.
When testing application throughput, RMON will provide better statistics in some instances. You can set up a "sender" and "receiver" and monitor real traffic. Larger enterprises generally have RMON monitors for critical applications. The cool advantage to RMON is that it allows you to move users around based on real time monitoring either via VLANs or just by adjusting who is plugged into which switch to share the loads when possible.
Bandwidth simulators are also a good way to stress test your network and plan for converged services. By being able to simulate traffic before it actually hits your network you can plan increased bandwidth where necessary, and spot potential problems before they become real ones. There are several available both shareware and purchasable products.
Physical layer testers are a bit different. These can be either field testers, smart bit testers, and/or spectrometers for radio frequency information. What you are testing will determine what type of tester you need. They key here is that the tester be calibrated just prior to the test and that the tester be certified by an independent agency. Test and Measurement World has a listing of testers, ratings for how well they perform, and certifications for each variety. You will want to be sure that your tester is certified by an independent testing source.
3Com has a free network management package on their Web site for download. CastleRock Computing allows a 30 day demo for their SNMPc product which was one of the first tools to read most equipment manufacturers' MIBs, and report the statistics into a single GUI interface. There are others as well -- some good and some not. Check reference accounts when in question. These tools will work with any network device that is SNMP manageable. It is always a good idea to do an autodiscovery periodically on your network to see what shows up in your subnet. Another benefit of using SNMP type management products is that you can see immediately if a switch port has autonegotiated to a slower speed than expected which could indicate physical problems or interference type problems.
Whatever management tool(s) you use, an ounce of prevention is certainly worth a pound of cure!
Carrie Higbie, Global Network Applications Market Manager, The Siemon Company
Carrie has been involved in the computing and networking industries for nearly 20 years. She has worked with manufacturing firms, medical institutions, casinos, healthcare providers, cable and wireless providers and a wide variety of other industries in both networking design/implementation, project management and software development for privately held consulting firms and most recently Network and Software Solutions.
Carrie currently works with The Siemon Company where her responsibilities include providing liaison services to electronic manufacturers to assure that there is harmony between the active electronics and existing and future cabling infrastructures. She participates with the IEEE, TIA and various consortiums for standards acceptance and works to further educate the end user community on the importance of a quality infrastructure. Carrie currently holds an RCDD/LAN Specialist from BICSI, MCNE from Novell and several other certifications.
