IPv6 Duplicate Address Detection | IPv6 DAD

IPv6 Duplicate Address Detection (DAD) is required to verify that only single host is using a particular IPv6 address to avoid to any conflict which may result in failure of communications.

Hosts can be configured with IPv6 address using one of the following methods
(1) Static configuration
(2)Stateful DHCP
(3)Stateless Address Auto-configuration (SLAAC)

DPD is a function using Neighbor Discovery Protocol (NDP) to find out any conflict in using IPv6 address

Host sends Neighbor Solicitation message to all other hosts on the network asking if any of them is using the same IPv6 address.

The other host using the same IPv6 address will send back a message called Neighbor Advertisement to the host and the first host, after this message, ignores to use the same IPv6 address.

source
ipv6