504 CHAPTER 38: IPV6 BASICS CONFIGURATION
Introduction to IPv6
Neighbor Discovery
Protocol
IPv6 Neighbor Discovery Protocol (NDP) uses five types of ICMPv6 messages to
implement the following functions:
■ “Address resolution” on page 504
■ “Neighbor reachability detection” on page 505
■ “Duplicate address detection” on page 505
■ “Router/prefix discovery and address autoconfiguration” on page 506
■ “Redirection” on page 506
Table 49 lists the types and functions of ICMPv6 messages used by the NDP.
The NDP mainly provides the following functions:
Address resolution
Similar to the ARP function in IPv4, a node acquires the link-layer addresses of
neighbor nodes on the same link through NS and NA messages. Figure 152 shows
how node A acquires the link-layer address of node B.
Table 49 Types and functions of ICMPv6 messages
ICMPv6 message Number Function
Neighbor solicitation (NS)
message
135 Used to acquire the link-layer address of a neighbor
Used to verify whether the neighbor is reachable
Used to perform a duplicate address detection
Neighbor advertisement
(NA) message
136 Used to respond to an NS message
When the link layer changes, the local node initiates
an NA message to notify neighbor nodes of the
node information change.
Router solicitation (RS)
message
133 After started, a node sends an RS message to
request the router for an address prefix and other
configuration information for the purpose of
autoconfiguration.
Router advertisement
(RA) message
134 Used to respond to an RS message
With the RA message suppression disabled, the
router regularly sends an RA message containing
information such as prefix information options and
flag bits.
Redirect message 137 When a certain condition is satisfied, the default
gateway sends a redirect message to the source
host so that the host can reselect a correct next hop
router to forward packets.
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