|3||DAD Success when NUT received no packet on Stateless Link-local address autoconfiguration||FAIL||X||X||X||Link0||Link0|
RFC 2461 Neighbor Discovery for IPv6 7.2.3. Receipt of Neighbor Solicitations A valid Neighbor Solicitation that does not meet any the following requirements MUST be silently discarded: - The Target Address is a "valid" unicast or anycast address assigned to the receiving interface [ADDRCONF], - The Target Address is a unicast address for which the node is offering proxy service, or - The Target Address is a "tentative" address on which Duplicate Address Detection is being performed [ADDRCONF]. If the Target Address is tentative, the Neighbor Solicitation should be processed as described in [ADDRCONF]. Otherwise, the following description applies. If the Source Address is not the unspecified address and, on link layers that have addresses, the solicitation includes a Source Link-Layer Address option, then the recipient SHOULD create or update the Neighbor Cache entry for the IP Source Address of the solicitation. If an entry does not already exist, the node SHOULD create a new one and set its reachability state to STALE as specified in Section 7.3.3. If an entry already exists, and the cached link-layer address differs from the one in the received Source Link-Layer option, the cached address should be replaced by the received address and the entry's reachability state MUST be set to STALE. If a Neighbor Cache entry is created the IsRouter flag SHOULD be set to FALSE. This will be the case even if the Neighbor Solicitation is sent by a router since the Neighbor Solicitation messages do not contain an indication of whether or not the sender is a router. In the event that the sender is a router, subsequent Neighbor Advertisement or Router Advertisement messages will set the correct IsRouter value. If a Neighbor Cache entry already exists its IsRouter flag MUST NOT be modified. If the Source Address is the unspecified address the node MUST NOT create or update the Neighbor Cache entry. After any updates to the Neighbor Cache, the node sends a Neighbor Advertisement response as described in the next section. 7.2.4. Sending Solicited Neighbor Advertisements A node sends a Neighbor Advertisement in response to a valid Neighbor Solicitation targeting one of the node's assigned addresses. The Target Address of the advertisement is copied from the Target Address of the solicitation. If the solicitation's IP Destination Address is not a multicast address, the Target Link-Layer Address option MAY be omitted; the neighboring node's cached value must already be current in order for the solicitation to have been received. If the solicitation's IP Destination Address is a multicast address, the Target Link-Layer option MUST be included in the advertisement. Furthermore, if the node is a router, it MUST set the Router flag to one; otherwise it MUST set the flag to zero. If the Target Address is either an anycast address or a unicast address for which the node is providing proxy service, or the Target Link-Layer Address option is not included, the Override flag SHOULD be set to zero. Otherwise, the Override flag SHOULD be set to one. Proper setting of the Override flag ensures that nodes give preference to non-proxy advertisements, even when received after proxy advertisements, and also ensures that the first advertisement for an anycast address "wins". If the source of the solicitation is the unspecified address, the node MUST set the Solicited flag to zero and multicast the advertisement to the all-nodes address. Otherwise, the node MUST set the Solicited flag to one and unicast the advertisement to the Source Address of the solicitation. If the Target Address is an anycast address the sender SHOULD delay sending a response for a random time between 0 and MAX_ANYCAST_DELAY_TIME seconds. Because unicast Neighbor Solicitations are not required to include a Source Link-Layer Address, it is possible that a node sending a solicited Neighbor Advertisement does not have a corresponding link- layer address for its neighbor in its Neighbor Cache. In such situations, a node will first have to use Neighbor Discovery to determine the link-layer address of its neighbor (i.e, send out a multicast Neighbor Solicitation).