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The Top 5 Free Network Monitoring Tools

written by: Lee Clemmer•edited by: Bill Bunter•updated: 5/5/2010

Awareness of what's happening on your network, and why, makes the difference between average and excellent network administration. Great tools are needed to obtain this knowledge quickly and accurately. Fortunately, some of the best network monitoring tools are free. This article lists the top five.

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    What Makes a Great Network Monitoring Tool?

    Some of the very best Network Monitoring Tools have always been free.

    Vendors sometimes even incorporate code based on RRDTool and MRTG into their products. Templates, free utilities, scripting, and a little web code can create a custom monitoring interface that's ideal for you and costs nothing more than the time to put it together.

    More advanced and detailed monitoring most often involves SNMP, which can have a steep learning curve for the beginner. Large amounts of data are generated and conted by monitoring tools. Some of this data is essentially invisible until you begin measuring and collecting it.

    Commercial tools can "hide" this complexity, which is one reason you might pay for them. The data is there if you're willing to make the effort to obtain it. Transforming it into useful, accurate information is what makes a great monitoring tool.

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    The Top Five

    1. MRTG - The Multi Router Traffic Grapher (MRTG) is primarily designed to monitor and graph traffic on network links. It is written in Perl, generates HTML with PNG image graphs, updated at configurable intervals. One of the best features is that it creates daily, weekly, and monthly graphs as well. You can monitor any SNMP variable you choose. In my opinion, MRTG is one of the best tools ever written for network monitoring.

    2. Cacti / RRDTool - Cacti is a front end to RRDTool, and uses a MySQL database for data storage. Data sources can be created and customized. The front end is written in PHP. Many templates are available, as well as the option to grant users permissions to view only or create new graphs.

    3. Nagios - Nagios goes beyond network monitoring to include notification and problem management, as well as other enterprise-class features. It has been around for over 10 years, has a large user base and support community. While some of the solutions in the top five are OS agnostic, Nagios runs on Linux or Unix. You can monitor any system or device with it, of course.

    4. Ntop - Ntop is focused specifically on network traffic monitoring. IP traffic and protocol information & statistics. Information can be sorted or detailed by host, subnet, or viewed in total for the network. Ntop works with NetFlow and sFlow as well. Interestingly, it can be compiled for Windows as well as Unix.

    5. Zenoss Core - If you're looking for an enterprise management platform for more than just the network, but don't have the budget for a commercial product, Zenoss has an open source alternative. Zenoss offers Professional and Enterprise versions with support and consulting available.

    Honorable Mentions

    SolarWinds Cisco Netflow v5 - This and several other SolarWinds free tools are excellent. If you have a Cisco network with Netflow this can get you started.

    Snort - Snort is technically an IDS (and one of the best), but can serve as a great application layer network analysis tool. I didn't include this or any other IDS as they are really a separate category.

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    Need More?

    Advanced monitoring, alerts, and reporting can be built from the tools in free and open source arena, but you or your management may decide that a commercial tool or platform is a better investment. Major network equipment vendors almost always integrate easily with the most common monitoring platforms, or those vendors provide plugins and templates for SNMP data from a wide variety of equipment. Tuning and filtering data, reports, and alerts so that the NOC or helpdesk isn't innundated with redundant or irrelevant data is a big part of integrating a monitoring solution for an enterprise. There are so many possible commercial solutions, and so many ways to implement them, that a "best" choice there is unique for each business, in my experience. Using these free tools, or others that you find, is a great way to augment your knowledge and awareness of the state and health of your network.