Duplicate address detection
After Host A acquires an IPv6 address, it performs Duplicate Address Detection (DAD) to check whether the address is being used by any other node. This is similar to gratuitous ARP in IPv4. DAD is accomplished through NS and NA messages.
The DAD procedure is as follows:
Host A sends an NS message. The source address is the unspecified address and the destination address is the corresponding solicited-node multicast address of the IPv6 address to be detected. The NS message body contains the detected IPv6 address.
If Host B uses this IPv6 address, Host B returns an NA message that contains its IPv6 address.
Host A knows that the IPv6 address is being used by Host B after receiving the NA message from Host B. If receiving no NA message, Host A decides that the IPv6 address is not in use and uses this address.
Figure 65: Duplicate address detection
