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Networking Fundamentals · Intermediate

Duplicate Address Detection (DAD)

An IPv6 process that checks whether an address is already in use on the link before assigning it.

Definition

The host sends a Neighbor Solicitation for its tentative address from the unspecified address; if a Neighbor Advertisement comes back, the address is a duplicate and is not used. DAD is performed for all unicast addresses, including link-local ones. IPv4 achieves similar results with ARP probes and gratuitous ARP.

Example

An interface stuck with a "duplicate" or "tentative" IPv6 address failed DAD.

Exam tip

DAD uses NS from :: to the solicited-node address of the tentative address.

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