Reader favorites: 10 great free network tools

From sniffing to mapping to monitoring, these utilities perform surprisingly sophisticated tasks

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Multi Router Traffic Grapher

I have written about Multi Router Traffic Grapher (MRTG) before, but it deserves mention here because it's such a useful program and is very popular among network administrators. There are other graphic monitor programs out there, but nothing beats this old standard.

MRTG, like most of these tools, is a program that provides a useful representation of data gleaned from standard sources. The most common MIB variable that is polled is interface traffic statistics, but any MIB variable can be graphed. MRTG requires a Web server, and default displays give one day, one week and one year statistics.

The methodology is simple: poll network devices every five minutes via SNMP for the desired variable(s) and then present data via a graph in a Web page covering three basic periods of time.

MRTG takes SNMP data and displays it graphically so baselines can be recorded, trends analyzed and anomalies detected -- not just in traffic flow but any aspect of a network device that has an SNMP MIB attribute.

MRTG takes SNMP data and displays it graphically so baselines can be recorded, trends analyzed and anomalies detected -- not just in traffic flow but any aspect of a network device that has an SNMP MIB attribute.

Click to view larger image

Using this data for traffic usage, for example, it's trivial to establish a baseline for "normal" traffic on your network and determine when perhaps you need to throw more money at bandwidth.

MRTG takes SNMP data and displays it graphically so baselines can be recorded, trends analyzed and anomalies detected not just in traffic flow but any aspect of a network device that has an SNMP MIB attribute.

Because MRTG presents SNMP data, any such data can be graphed. It's not uncommon to graph ambient temperature, CPU utilization or number of connected clients. The bottom line, if SNMP can report it, MRTG can graph it. Of course, because the data is displayed as an HTML page, it can be accessed from anywhere on the Internet, or standard controls such as .htaccess passwords can limit access to the data to authorized personnel.

SNMP Traffic Grapher

Like its big cousin, MRTG, SNMP Traffic Grapher (STG) takes SNMP data and presents it in a graph form. But it doesn't need a back-end Web server, nor does it need to be refreshed every time statistics are updated. Think of STG as a real-time MRTG application. In fact, it was developed to be a companion to MRTG.

Like MRTG, STG displays in a graphical format any SNMP MIB variable, such as inbound and outbound traffic as shown here. Its strength lies in its real-time acquisition and display of data.

Like MRTG, STG displays in a graphical format any SNMP MIB variable, such as inbound and outbound traffic as shown here. Its strength lies in its real-time acquisition and display of data.

Click to view larger image

STG can provide timely information just when you need it most. Think of when you want to make a network change and you're worried how it will affect traffic. Maybe you're loosening restrictions and afraid the egress bandwidth will spike. Or perhaps you're activating VPN on your firewall and are worried that CPU utilization will go up.

STG, like MRTG, can graph any SNMP MIB variable, but the difference is that information is displayed in real time. That's its main strength. STG is as configurable as it needs to be; enter the MIB value, the polling time and the display output. That's all.

Like MRTG, STG displays in a graphical format any SNMP MIB variable, such as inbound and outbound traffic as shown here.

STG is invaluable not so much for trending (use MRTG for that) but for checking in real time how network changes affect performance. We often have to make changes we don't want to in the middle of the business day. Knowing how that affects performance before the end user notices problems is essential.

Despite its usefulness, there doesn't appear to have been any recent development on STG. However, others have created similar tools such as Paessler Router Traffic Grapher. I discovered this while researching this article and plan to evaluate it at a future date.

What else?

Don't forget that it may be worthwhile to learn rudimentary Linux administration skills so you can use other sophisticated open-source tools to manage your network.

Everyone has their favorite tools in their bag of tricks. Have we missed one of yours? Perhaps you have evaluated some of the reviewed tools or others mentioned in this article and want to share what you've learned. If so, let us know in the article comments section or by e-mail to david_ramel@computerworld.com

Greg Schaffer is a freelance writer in Tennessee. He has over 15 years of experience in networking, primarily in higher education. He can be reached at newtnoise@comcast.net.

Copyright © 2008 IDG Communications, Inc.

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