SixXS's Ghost Route Hunter (GRH) is an IPv6 Route Collector which does periodic analysis of the state of the IPv6 routing tables, allowing users of this public and free tool to easily find out problems in those tables, provided by a large number of ISP's from all around the world.

telnet: grh.sixxs.net
tools accessible through website at http://www.sixxs.net/tools/grh/