When an interface gets a valid Neighbor Solicitation message the node behavior depends whether the target address is tentative or not.
if its not tentative the solicitation is processed.
if the target address is tentative, and the source address is a unicast address, the solicitation's sender is performing address resolution on the target; the solicitation should be silently ignored. Otherwise, processing takes place as described below. In all cases, a node MUST NOT respond to a Neighbor Solicitation for a tentative address.
there is few cases :
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The source address of the Neighbor Solicitation is the unspecified address, the solicitation is from a node performing Duplicate Address Detection. |
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The solicitation is from another node, the tentative address is a duplicate and should not be used (by either node). |
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The solicitation is from the node itself (because the node loops back multicast packets), the solicitation does not indicate the presence of a duplicate address. |
The following tests identify conditions under which a tentative address is not unique:
F If a Neighbor Solicitation for a tentative address is received prior to having sent one, the tentative address is a duplicate. This condition occurs when two nodes run Duplicate Address Detection simultaneously, but transmit initial solicitations at different times (e.g., by selecting different random delay values before transmitting an initial solicitation).
F If the actual number of Neighbor Solicitations received exceeds the number expected based on the loopback semantics (e.g., the interface does not loopback packet, yet one or more solicitations was received), the tentative address is a duplicate. This condition occurs when two nodes run Duplicate Address Detection simultaneously and transmit solicitations at roughly the same time.
