BandwidthD is a network subnet tracker that monitors TCP/IP network subnets and generates HTML files with graphs displaying network utilization. It provides detailed charts for individual IP addresses, illustrating utilization over various periods like 2 days, 8 days, 40 days, and 400 days. Users can log IP utilization at intervals ranging from 3.3 minutes to 12 hours in cdf format or to a backend database server. The program color-codes HTTP, TCP, UDP, ICMP, VPN, and P2P traffic for easy identification.

BandwidthD is compatible with Windows and Unix platforms, requiring only libpcap, libgl, and libpng libraries for Unix. It offers two output modes: standalone application producing static html and png output every 200 seconds, and a sensor transmitting data to a backend database for dynamic PHP reporting.