So much is involved with monitoring networks. What makes a tool or platform the best? All of the more advanced monitoring solutions will include Simple Network Management Protocol (SNMP) support. SNMP is more complex and more difficult to set up than truly simpler means of monitoring, but is worth it for depth and accuracy. Monitoring data is present in many of your nodes, but useless until you begin measuring and collecting it. Commercial tools can be more comprehensive, and offer support and service--but this comes with a cost. In my opinion some of the open source solutions are as good or better than the commercial offerings in many ways.
Here are my top ten, in alphabetical order:
1. Big Brother - Aimed at being low-cost and having a small footprint, Big Brother supports hundreds of network devices and monitors all aspects of your network. It can monitor processes, applications, event logs as well as network functions.
2. GFI Network Server Monitor - This product's target is much more on the server and application side, but can monitor network devices as well. Customizable monitoring functions and out-of-the-box support for enterprise applications are notable.
3. HP OpenView - OpenView has long been one of the commercial monitoring platforms with great breadth and depth. A commercial product with proven enterprise support capability, OpenView has been around over 15 years, and the suite of products has remained first class. OpenView is now the foundation of part of HP's BTO product line.
4. MRTG - The Multi Router Traffic Grapher (MRTG) monitors and graphs traffic on network links. One of the best features is that it creates daily, weekly, and monthly graphs as well. Beyond just traffic, you can graph any SNMP variable.
5. Nagios - Nagios is an open source solution that along with network monitoring includes notification and problem management, as well as other enterprise-class features. Nagios runs on Linux, has been around for over 10 years, and has a large user base & support community.
6. Ntop - Another open source network traffic monitoring platform, Ntop looks at IP traffic, protocol information and statistics. Sort the collected information by host, subnet, or look at the whole network. Ntop compiles on Windows and Unix.
7. OpenNMS - OpenNMS is an open source network monitoring platform aimed at enterprises. OpenNMS offers training, support, and service commercially, with a strong user and open source community support group as well.
8. SolarWinds Orion Network Performance Monitor - Orion NPM is aimed both at simplicity and ease while providing enterprise class SNMP monitoring support. Solarwinds is famous for many excellent free network tools.
9. Spiceworks IT Management - Spiceworks is a free, ad sponsored network monitoring and issue tracking platform. Spiceworks has a large, active user community and has a very customizable interface. See my review of Spiceworks here.
10. Zenoss - Zenoss is an enterprise management platform that is open source, intending to offer all the features of a commercial product. Zenoss offers support and consulting for the Professional and Enterprise versions.
With so many solutions, and so many ways to implement them the right choice for one business may be wrong for another. Keep in mind that free tools can augment the monitoring platform you have purchased and standardized on. Also see my article on the Top Five Free Network Monitoring Tools.