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2 Verify whether neighbors are reachable

After obtaining the link layer address of neighbor node, neighbor request message NS and

neighbor notification message NA can verify whether neighbor node is reachable or not。

(1) The node sends the NS message, where the destination address is the IPv6 address of

the neighbor node。

(2) If the acknowledgement message of neighbor node is received, the neighbor is

reachable; otherwise, the neighbor is unreachable。

3 Duplicate address detection

When a node acquires an IPv6 address, it is necessary to use the repeated address detection

function to determine whether the address has been used by other nodes (similar to the free ARP

function of IPv4). Duplicate address detection can be implemented by NS and NA, as shown in

Figure 1-4。

Fig. 1-4 duplicate address detection schematic diagram

(1) The node A sends the NS message, and the source address of the NS message is an

unspecified address: the destination address is the multicast address of the requested node

corresponding to the IPv6 address to be detected, and the message content contains the IPv6

address to be detected。

(2) If the node B has already used this IPv6 address, the NA message will be returned. It

contains its own IPv6 address。

(3) The node A receives the NA message from the node B, and knows that the IPv6 address

is already in use. Otherwise, the address is not used, and the node A can use the IPv6 address。

4 Router discovery / prefix discovery and address auto configuration

Router discovery / prefix discovery is that the node obtains the prefix of neighbor router and

its network from the received RA message, and other configuration parameters。

Address stateless automatic configuration refers to the node to discover the acquired

information according to the router discovery / prefix, and automatically configure the IPv6

address. The router discovery / prefix discovery is implemented through the router request

message RS and the router notification message RA, and the specific process is as follows：

(1) When the node starts, it sends a request to the router through the RS message,

requesting the prefix and other configuration information for the configuration of the node。

(2) The router returns the RA message, including prefix information options (the router also

periodically releases RA messages)。

(3) The node automatically configures the IPv6 address and other information of the

interface by using the address prefix and other configuration parameters in the RA message

returned by the router。

 Prefix information options include not only the address prefix information, but also the