IPv6 Overview 505
Figure 152 Address resolution
The address resolution procedure is as follows:
1 Node A multicasts an NS message. The source address of the NS message is the
IPv6 address of an interface of node A and the destination address is the
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 corresponds to the solicited-node multicast address. If yes, node B can
learn the link-layer address of node A, and unicasts an NA message containing its
link-layer address.
3 Node A acquires the link-layer address of node B from the NA message.
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.
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 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. Figure 152 shows the DAD procedure.
Figure 153 Duplicate address detection
ICMP type = 135
Src = A
Dst = solicited-node multicast address of B
Data = link layer address of A
NS
ICMP type = 136
Src = B
Dst = A
Data = link layer address of B
NA
Host A Host B
ICMP type = 135
Src = ::
Dst = FF02::1:FF00:1
Data = 2000::1
NS
ICMP type = 136
Src = 2000::1
Dst = FF02::1
Target address = 2000::1
NA
Host A Host B
2000::1
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