HPE 3100 Configuration Manual page 126

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 IPv4).
DAD is accomplished through NS and NA message exchanges.
Figure 54 Duplicate address detection
1. Host A sends an NS message whose source address is the unspecified address and whose
destination address is the corresponding solicited-node multicast address of the IPv6 address
to be detected. The NS message contains the IPv6 address.
2. If Host B uses this IPv6 address, Host B returns an NA message. The NA message contains the
IPv6 address of Host B.
3. Host A learns that the IPv6 address is being used by Host B after receiving the NA message
from Host B. If receiving no NA message, Host A decides that the IPv6 address is not in use and
uses this address.
Router/prefix discovery and address autoconfiguration
Router/prefix discovery enables a node to locate the neighboring routers and to learn from the
received RA message configuration parameters such as the prefix of the network where the node is
located.
Stateless address autoconfiguration enables a node to generate an IPv6 address automatically
according to the information obtained through router/prefix discovery.
Router/prefix discovery is implemented through RS and RA messages in the following steps:
1. At startup, a node sends an RS message to request the address prefix and other configuration
information for autoconfiguration.
2. A router returns an RA message containing information such as Prefix Information options.
(The router also periodically sends an RA message. In addition to an address prefix, the Prefix
Information option also contains the preferred lifetime and valid lifetime of the address prefix.
Nodes update the preferred lifetime and valid lifetime accordingly through periodic RA
messages.)
3. The node automatically generates an IPv6 address and other configuration information
according to the address prefix and other configuration parameters in the RA message. (The
automatically generated address is applicable within the valid lifetime and is removed when the
valid lifetime expires.)
Redirection
A newly started host may contain only a default route to the gateway in its routing table. When certain
conditions are satisfied, the gateway sends an ICMPv6 Redirect message to the source host, so the
host can select a better next hop to forward packets (similar to the ICMP redirection function in IPv4).
The gateway sends an ICMPv6 Redirect message when the following conditions are satisfied.
Figure 54
116
shows the DAD process.