IPv6 Overview 531solicited-node multicast address of node B. The NS message contains the link-layeraddress of node A.2 After receiving the NS message, node B judges whether the destination address ofthe packet is the corresponding solicited-node multicast address of its own IPv6address. If yes, node B learns the link-layer address of node A and returns an NAmessage containing the link-layer address of node B in the unicast mode.3 Node A acquires the link-layer address of node B from the NA message. After that,node A and node B can communicate with each other.Neighbor unreachability detectionAfter node A acquires the link-layer address of its neighbor node B, node A canverify whether node B is reachable according to NS and NA messages.1 Node A sends an NS message whose destination address is the IPv6 address ofnode B.2 If node A receives an NA message from node B, node A considers that node B isreachable. Otherwise, node B is unreachable.Duplicate address detectionAfter a node acquires an IPv6 address, it should perform the duplicate addressdetection to determine whether the address is being used by other nodes (similarto the gratuitous ARP function). The duplication address detection is accomplishedthrough NS and NA messages. Figure 192 shows the duplicate address detectionprocedure.Figure 192 Duplicate address detectionThe duplicate address detection procedure is as follows:1 Node A sends an NS message whose source address is the unassigned address ::and the destination address is the corresponding solicited-node multicast addressof the IPv6 address to be detected. The NS message also contains the IPv6 address.2 If node B uses this IPv6 address, node B returns an NA message. The NA messagecontains the IPv6 address of node B.3 Node A learns that the IPv6 address is being used by node B after receiving the NAmessage from node B. Otherwise, node B is not using the IPv6 address and node Acan use it.Src=::ICMP type=136Src=2000::1Dst=FF02::1Target address =2000::1NSNAA BICMP type=135Data=2000::1Dst=FF02::1:FF00:1
