15-7
ICMPv6 message
Type
Function
Responds to an RS message.
Router Advertisement (RA)
message
134
Advertises information such as the Prefix Information
options and flag bits (with the RA message suppression
function disabled).
Redirect message
137
Informs the source host of a better next hop on the path to a
particular destination when certain conditions are satisfied.
Address resolution
Similar to the ARP function in IPv4, an IPv6 node acquires the link-layer addresses of
neighboring nodes on the same link through NS and NA messages.
shows how
Host A acquires the link-layer address of Host B on a single link.
Figure 15-3
Address resolution
The address resolution process is:
1) Host A multicasts an NS message. The source address of the NS message is the IPv6
address of the sending interface of Host A and the destination address is the solicited-node
multicast address of Host B. The NS message contains the link-layer address of Host A.
2) After receiving the NS message, Host B judges whether the destination address of the
packet is its solicited-node multicast address. If yes, Host B learns the link-layer address of
Host A, and then unicasts an NA message containing its link-layer address.
3) Host A acquires the link-layer address of Host B from the NA message.
Neighbor reachability detection
After Host A acquires the link-layer address of its neighbor Host B, Host A can use NS and NA
messages to check whether Host B is reachable.
1) Host A sends an NS message whose destination address is the IPv6 address of Host B.
2) If Host A receives an NA message from Host B, Host A decides that Host B is reachable.
Otherwise, Host B is unreachable.
Duplicate address detection
After Host A acquires an IPv6 address, it performs Duplicate Address Detection (DAD) to check
whether the address is being used by any other node (similar to the gratuitous ARP function in