1-72) After receiving the NS message, node B judges whether the destination address of the packet is itssolicited-node multicast address. If yes, node B learns the link-layer address of node A, and thenunicasts an NA message containing its link-layer address.3) Node A acquires the link-layer address of node B from the NA message.Neighbor reachability detectionAfter node A acquires the link-layer address of its neighbor node B, node A can verify whether node B isreachable according to NS and NA messages.1) Node A sends an NS message whose destination address is the IPv6 address of node B.2) If node A receives an NA message from node B, node A considers that node B is reachable.Otherwise, node B is unreachable.Duplicate address detectionAfter node A acquires an IPv6 address, it will perform duplicate address detection (DAD) to determinewhether the address is being used by any other node (similar to the gratuitous ARP function of IPv4).DAD is accomplished through NS and NA messages. Figure 1-4 shows the DAD procedure.Figure 1-4 Duplicate address detectionThe DAD procedure is as follows:1) Node A sends an NS message whose source address is the unassigned address :: and destinationaddress is the corresponding solicited-node multicast address of the IPv6 address to be detected.The NS message contains the IPv6 address.2) If node B uses this IPv6 address, node B returns an NA message. The NA message contains theIPv6 address of node B.3) Node A learns that the IPv6 address is being used by node B after receiving the NA message fromnode B. Otherwise, node B is not using the IPv6 address and node A can use it.Router/prefix discovery and address autoconfigurationRouter/prefix discovery means that a node locates the neighboring routers, and learns the prefix of thenetwork where the host is located, and other configuration parameters from the received RA message.Stateless address autoconfiguration means that a node automatically generates an IPv6 addressaccording to the information obtained through router/prefix discovery.The router/prefix discovery is implemented through RS and RA messages. The router/prefix discoveryprocedure is as follows:1) After started, a node sends an RS message to request the router for the address prefix and otherconfiguration information for the purpose of autoconfiguration.
