NScan is one of the most fast and flexible portscanners for Windows, which is designed for scanning large networks and gathering related network/host information. In fact, it's not just a portscanner, but a kit for testing network security and reliability, which can solve numerous problems on your network. A set of utilities extends it's capabilities and allows you to do most of the general diagnostics quickly and easily.

The utilities setting currently contains a fast parallel UDP traceroute that traces all the way to the host in one or two seconds, making route discovery ten times faster and identifying the client easier. It supports automatic correct information source recognition, has runtime history and some other useful custom features, like data source set extendibility, and, finally, TCP-based DNS client that supports most of the available options, including AXFR zone transfer. Portscanner itself also supports remote monitoring, usage of host and port lists, option profiles, speed and accuracy tuning, etc.