3Com Switch 4800G 24-Port Configuration Manual page 506

506 C 38: IP 6 B
HAPTER V ASICS
n
C
ONFIGURATION
The DAD procedure is as follows:
1 Node A sends an NS message whose source address is the unassigned address ::
and 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 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.
Router/prefix discovery and address autoconfiguration
Router/prefix discovery means that a node locates the neighboring routers, and
learns the prefix of the network where the host is located, and other configuration
parameters from the received RA message.
Stateless address autoconfiguration means that a node automatically configures
an IPv6 address according to the information obtained through router/prefix
discovery.
The router/prefix discovery is implemented through RS and RA messages. The
router/prefix discovery procedure is as follows:
1 After started, a node sends an RS message to request the router for the address
prefix and other configuration information for the purpose of autoconfiguration.
2 The router returns an RA message containing information such as prefix
information option. (The router also regularly sends an RA message.)
3 The node automatically configures an IPv6 address and other information for its
interface according to the address prefix and other configuration parameters in
the RA message.
In addition to an address prefix, the prefix information option also contains the
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preferred lifetime and valid lifetime of the address prefix. After receiving a
periodic RA message, the node updates the preferred lifetime and valid lifetime
of the address prefix accordingly.
An automatically generated address is applicable within the valid lifetime and
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will be removed when the valid lifetime times out.
Redirection
When a host is started, its routing table may contain only the default route to the
gateway. When certain conditions are satisfied, the gateway sends an ICMPv6
redirect message to the source host so that the host can select a better next hop to
forward packets (similar to the ICMP redirection function in IPv4).
The gateway will send an IPv6 ICMP redirect message when the following
conditions are satisfied:
The receiving interface is the forwarding interface.
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The selected route itself is not created or modified by an IPv6 ICMP redirect
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message.