Network Troubleshooting Tips

Well, I’m returning from a much needed vacation, getting back into the grind of things, and decided it’s high time to post some more useful articles for my readers. So, thank you for your patience, and – I’m back (and better than ever!)

Of the many services that Eberly Systems has been offering to our clients throughout the last 3 years, Network Design, installation and support has been perhaps our highest demand and best niche service (I use the term “niche” a bit loosely here).

Over the past few months in particular, we’ve tackled a number of Data, Fiber and Engineering projects for some of our larger clients, and I thought it might be useful to our readers to discuss some of the tools and strategies that really carry us through the “Tough Ones”. Enjoy – and if you learn something or appreciate this information, be sure to tell someone about it!!

The Tool Box
Of the many tools and utilities available to a Network Professional, here are a few (both Hardware and Software) that I find indispensable. FYI – check out Wikipedia for the OSI Model if you aren’t familiar with it.

– Physical Layer (OSI #1), Cabling, Fiber
Whether you are testing Fiber and need a simple Power Meter / Light Source, step up to an OTDR (Optical Time Domain Relectometer), or you’re on Copper and utilize a LanCat / DTX / DSP (or similar) Cat5 or Cat6 Network Analyzer, you will find that Link and Channel testing is a CRITICAL first-step any time you come up against a real “bear” of a challenge. Without confidence in your basic link and infrastructure, every other piece of data and information that you gather is potentially faulty and unreliable.

– Link Testing
When you step up to Layer 2 testing, we start to break out the software utilities.
Every Analyst has their own special “routine” and “bag of tricks”, but we all have similar tools. Eberly Systems still (for the moment) relays primarily on Windows based software tools, but many professionals prefer Linux (of varying flavors) for Network troubleshooting, as in many cases it provides a more complete and fine-tuned suite of tools and commands for performing traces and collecting crucial network info. For now, I’m not going into any of those, because (as previously stated), we’re still on Windows.

Our most basic Data Link, Network and Transport Layer test utilities are ‘ping’ and ‘tracert’. While SUPER basic in their operation and data-gathering capabilities, in a complex Business network, when utilized with the appropriate switches and analyzed by an experienced eye, these two simple utilities can often pinpoint a problem down to a particular device or section of cable/fiber.

‘Ping’ is a simple utility that sends an ICMP packet and posts response times from a single device. By analyzing response times (latency) and variations (or lack thereof) in the results, we can often discover a device or cabling issue very quickly.
“Tracert” is slightly more complex, but utilizes the same protocols and basic principles to send ICMP probes across a network to any endpoint and record responses and latencies from EVERY DEVICE that it routes through on it’s journey. This can be particularly useful in determining whether a Connectivity issue is on your local network / subnet or somewhere “further out” (i.e. Do I call my Network guy or do I call my Internet Service Provider?)
Google “ping switches” or “tracert commands” to learn more about these two utilities.

– Network Monitoring
One of the more advanced (and powerful) tools that we utilize in more complicated scenarios is SNMP monitoring. SNMP (Simple Network Monitoring Protocol) allows for detailed data logging of traffic from any SNMP enabled device on your network (and 9 out of 10 Network devices ARE SNMP enabled or at least capable).
Utilizing a good SNMP utility (such as Paessler Network Traffic Grapher or similar), you can log and graph traffic and bandwidth patterns across entire networks, quickly identifiying problem devices, bandwidth hogs, or problem links with a simple check of your recorded data.

While expensive for an enthusiast, Paessler’s software is a crucial tool for any Network Professional.
Free alternatives (such as MRTG, with or with out RRDTool) offer similar features, but with much more hassle and expertise required for setup and configuration.

Another inseparable tool for Network Monitoring is Wireshark. Wireshark allows you to “sniff” and capture network traffic, enabling you to analyze specific usage and download data, session problems (caused by misconfiguration or faulty hardware), and LOTS of other very useful information. HOWEVER – Wireshark is not for the faint-of-heart. It often provides so MUCH data that it requires a cool head and time (and practice) to really be able to sift through and pinpoint the useful information. Also, to capture all traffic over a segment, Wireshark should be configured on a Gateway computer, so that all traffic filters directly through the Wireshark computer. The alternative (which is simpler) allows capturing in “Promiscuous Mode”, but is not able to log ALL data, and may miss entire connections during heavy activity times.

There you go – that’s the basic tools required to solve MOST network issues. Of course, if you know a good Network company, why bother with the troubleshooting yourself? Give us a call – we’d love to help you solve your Network problem, quickly and thoroughly!