ipv6mon is a tool meant for monitoring IPv6 address usage on a local
network.  It is meant to be particularly useful in networks that employ
IPv6 Stateless Address Auto-Configuration (as opposed to DHCPv6),
where address assignment is decentralized and there is no central
server that records which IPv6 addresses have been assigned to which
nodes during which period of time.

WWW: https://www.si6networks.com/tools/ipv6mon/