PRTG - Paessler Router Traffic Grapher, the free and simple solution for monitoring and classifying your bandwidth usage.
    A very useful tool for system administrators provides real time readings and long-term usage trends for all their network devices. This tool can receive bandwidth and network usage data that helps to optimize the efficiency of your network. With support to SNMP, packet sniffing and netflow protocol tools this application can easily monitor and classify your bandwidth usage. This software works with all switches, routers, firewalls, as well as many other network devices. Its monitoring engine is capable of monitoring thousands of sensors at a time. It can even store the recorded data for later reference. It has its own Web Interface and a built in web server to access graphs and tables using any web browser.
    This multipurpose software works with SNMP network devices, and tested with routers and switches from Cisco, HP, 3Com, Linksys and DLink.