A host performing Duplicate Address Detection (DAD) sends a Neighbor Solicitation for a tentative IPv6 address. Which reception indicates DAD has failed and the address is duplicate?
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Correct answer: Receiving a Neighbor Advertisement or another Neighbor Solicitation claiming the same target address.
Why this is the answer
Duplicate Address Detection (DAD) uses Neighbor Solicitation (NS) and Neighbor Advertisement (NA) messages to ensure an IPv6 address is unique on a link. When a host sends an NS for a tentative address, receiving an NA or another NS with the same target address indicates that another device is already using or attempting to use that address. This confirms a duplicate, causing DAD to fail. An ICMPv6 Time Exceeded message is not directly related to DAD failure. No response within the timeout period indicates the address is likely unique, not duplicate. Assigning a deprecated address is a separate address state and not a direct outcome of DAD failure due to a duplicate.
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