13-6Introduction to IPv6 Neighbor Discovery ProtocolThe IPv6 Neighbor Discovery Protocol (NDP) uses five types of ICMPv6 messages to implement thefollowing functions:z Address resolutionz Neighbor reachability detectionz Duplicate address detectionz Router/prefix discovery and address autoconfigurationz RedirectionTable 13-3 lists the types and functions of ICMPv6 messages used by the NDP.Table 13-3 Types and functions of ICMPv6 messagesICMPv6 message Number FunctionUsed to acquire the link-layer address of a neighborUsed to verify whether the neighbor is reachableNeighbor solicitation (NS)message 135Used to perform a duplicate address detectionUsed to respond to an NS messageNeighbor advertisement(NA) message 136 When the link layer changes, the local node initiatesan NA message to notify neighbor nodes of the nodeinformation change.Router solicitation (RS)message 133After started, a node sends an RS message to requestthe router for an address prefix and otherconfiguration information for the purpose ofautoconfiguration.Used to respond to an RS messageRouter advertisement(RA) message 134 With the RA message suppression disabled, therouter regularly sends an RA message containinginformation such as prefix information options and flagbits.Redirect message 137When a certain condition is satisfied, the defaultgateway sends a redirect message to the source hostso that the host can reselect a correct next hop routerto forward packets.The NDP mainly provides the following functions:Address resolutionSimilar to the ARP function in IPv4, a node acquires the link-layer addresses of neighbor nodes on thesame link through NS and NA messages. Figure 13-3 shows how node A acquires the link-layeraddress of node B.
