The Multi Router Traffic Grapher (MRTG) is a tool to monitor the traffic load on network links. MRTG generates HTML pages containing graphical images, which provide a LIVE visual representation of the traffic on the links. MRTG is widely used, currently mostly over IPv4. IPv6 support has been tested on Linux only, but should work on other operating systems such as FreeBSD.
Examples of implementations in 6NET:
GARR: http://www.uniroma3.6net.garr.it/mrtg/graphs/gsr.html
RENATER: http://supervision-ipv6.renater.fr
PSNC : http://www.ipv6.man.poznan.pl/