3Com S7906E Configuration Manual page 464

Figure 1-4 Duplicate address detection
The DAD procedure is as follows:
1) Node A sends an NS message whose source address is the unassigned address :: and destination
address 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 the
IPv6 address of node B.
3) Node A learns that the IPv6 address is being used by node B after receiving the NA message from
node B. Otherwise, the IPv6 address is not in use and node A can use it.
Router/prefix discovery and address autoconfiguration
Router/prefix discovery means that a node locates the neighboring routers, and learns the prefix of the
network where the node is located, and other configuration parameters from the received RA message.
Stateless address autoconfiguration means that a node automatically generates an IPv6 address
according to the information obtained through router/prefix discovery.
The router/prefix discovery is implemented through RS and RA messages. The router/prefix discovery
procedure is as follows:
1) After started, a node sends an RS message to request the router for the address prefix and other
configuration information for the purpose of autoconfiguration.
2) The router returns an RA message containing information such as prefix information option. (The
router also regularly sends an RA message.)
3) The node automatically generates an IPv6 address and other information for its interface according
to the address prefix and other configuration parameters in the RA message.
In addition to an address prefix, the prefix information option also contains the preferred lifetime
and valid lifetime of the address prefix. After receiving a periodic RA message, the node updates
the preferred lifetime and valid lifetime of the address prefix accordingly.
An automatically generated address is applicable within the valid lifetime and is removed when the
valid lifetime times out.
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