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Neighbor Reachability Detection
After node A acquires the link-layer address of its neighbor node B, node A can verify whether
node B is reachable according to NS and NA messages.
Node A sends an NS message whose destination address is the IPv6 address of node B.
If node A receives an NA message from node B, node A considers that node B is reachable.
Otherwise, node B is unreachable.
Duplicate Address Detection
Neighbor solicitation messages are used in the stateless autoconfiguration process to verify
the uniqueness of unicast IPv6 addresses before the addresses are assigned to an interface.
After node A acquires an IPv6 address, it will perform duplicate address detection (DAD) to
determine whether the address is being used by other nodes (similar to the gratuitous ARP
function of IPv4). DAD is accomplished through NS and NA messages. The DAD procedure is
as follows:
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.
If node B uses this IPv6 address, node B returns an NA message. The NA message
contains the IPv6 address of node B.
Node A learns that the IPv6 address is being used by node B after receiving the NA
message from node B. Otherwise, node B is not using the IPv6 address and node A can
use it.
2. IPv6 Router Advertisement Message
Router advertisement (RA) messages, which have a value of 134 in the Type field of the ICMP
packet header, are periodically sent out each configured interface of an IPv6 router.
RA messages typically include the following information:
One or more onlink IPv6 prefixes that nodes on the local link can use to automatically
configure their IPv6 addresses.
Lifetime information for each prefix included in the advertisement.
Sets of flags that indicate the type of autoconfiguration (stateless or stateful) that can be
completed.
Default router information (whether the device sending the advertisement should be used
as a default router and, if so, the amount of time, in seconds, the device should be used as
a default router).
Additional information for hosts, such as the hop limit and maximum transmission unit (MTU)
a host should use in packets that it originates.
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