IPv6 Overview 531
solicited-node multicast address of node B. The NS message contains the link-layer
address of node A.
2 After receiving the NS message, node B judges whether the destination address of
the packet is the corresponding solicited-node multicast address of its own IPv6
address. If yes, node B learns the link-layer address of node A and returns an NA
message containing the link-layer address of node B in the unicast mode.
3 Node A acquires the link-layer address of node B from the NA message. After that,
node A and node B can communicate with each other.
Neighbor unreachability 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.
1 Node A sends an NS message whose destination address is the IPv6 address of
node B.
2 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
After a node acquires an IPv6 address, it should perform the duplicate address
detection to determine whether the address is being used by other nodes (similar
to the gratuitous ARP function). The duplication address detection is accomplished
through NS and NA messages.
Figure 192 shows the duplicate address detection
procedure.
Figure 192 Duplicate address detection
The duplicate address detection procedure is as follows:
1 Node A sends an NS message whose source address is the unassigned address ::
and the destination address is the corresponding solicited-node multicast address
of the IPv6 address to be detected. The NS message also 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, node B is not using the IPv6 address and node A
can use it.
Src=::
ICMP type=136
Src=2000::1
Dst=FF02::1
Target address=2000::1
NS
NA
AB
ICMP type=135
Data=2000::1
Dst=FF02::1:FF00:1
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