DAD

networking

Stands for: Duplicate Address Detection

An IPv6 check that a chosen address is not already in use.

Duplicate Address Detection (RFC 4862) has a node send a neighbor solicitation for its own tentative address before using it; if anyone answers, the address is a duplicate and cannot be claimed.

Duplicate address detection is the check an IPv6 host performs before using an address, sending a neighbour solicitation for its own candidate address and treating any answer as proof someone else has it. It runs on every address including the link-local one.

The failure it produces is distinctive: an interface that comes up and then has no usable address, logged as a duplicate. The usual causes are a genuinely duplicated static assignment, a loop that reflects the host's own solicitation back to it, or a network with a device answering for everything. That second case is worth remembering, because a switching loop presents as an addressing failure rather than as a loop, and the message points at the wrong layer.

Also known as: dad

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