after a host has generated an ipv6 address by using the dhcpv6 or slaac process, how does the host verify that the address is unique and therefore usable?
The host verifies that the IPv6 address is unique by performing Duplicate Address Detection (DAD) using ICMPv6 Neighbor Solicitation.
Quick Scoop
After an IPv6 address is generated via DHCPv6 or SLAAC, the host:
- Temporarily marks the new address as “tentative,” meaning it is not yet fully usable on the interface.
- Sends an ICMPv6 Neighbor Solicitation (NS) message where the target address is the newly generated IPv6 address.
- Listens for an ICMPv6 Neighbor Advertisement (NA) in response:
- If no Neighbor Advertisement is received within a short timeout, the host assumes no other node is using that address , so it considers the address unique and fully assigns it to the interface.
* If a **Neighbor Advertisement is received** , this signals that **another host already uses that address** , so the address is considered duplicate and unusable, and the host must not use it and will typically try another address.
In exam-style wording, the correct statement is:
The host sends an ICMPv6 Neighbor Solicitation message to the DHCPv6- or SLAAC-learned address, and if no Neighbor Advertisement is returned, the address is considered unique and usable.
This DAD step is run for both link-local and global unicast IPv6 addresses whenever they are newly assigned.
Information gathered from public forums or data available on the internet and portrayed here.
