178IPv6 ND protocolThe IPv6 Neighbor Discovery (ND) protocol uses the following ICMPv6 messages:Table 8 ICMPv6 messages used by NDICMPv6 message Type FunctionNeighbor Solicitation (NS) 135Acquires the link-layer address of a neighbor.Verifies whether a neighbor is reachable.Detects duplicate addresses.Neighbor Advertisement(NA) 136Responds to an NS message.Notifies the neighboring nodes of link layer changes.Router Solicitation (RS) 133 Requests an address prefix and other configuration informationfor autoconfiguration after startup.Router Advertisement (RA) 134Responds to an RS message.Advertises information, such as the Prefix Information optionsand flag bits.Redirect 137 Informs the source host of a better next hop on the path to aparticular destination when certain conditions are met.Address resolutionThis function is similar to ARP in IPv4. An IPv6 node acquires the link-layer addresses of neighboringnodes on the same link through NS and NA messages. Figure 69 shows how Host A acquires thelink-layer address of Host B on the same link.Figure 69 Address resolutionThe address resolution procedure is as follows:1. Host A multicasts an NS message. The source address of the NS message is the IPv6 address of thesending interface of Host A and the destination address is the solicited-node multicast address ofHost B. The NS message body contains the link-layer address of Host A and the target IPv6address.2. After receiving the NS message, Host B determines whether the target address of the packet is itsIPv6 address. If yes, Host B learns the link-layer address of Host A, and then unicasts an NAmessage containing its link-layer address.3. Host A acquires the link-layer address of Host B from the NA message.
