Ipv6 Path Mtu Discovery - HP FlexNetwork MSR2003 Configuration Manual

Figure 83 Duplicate address detection
1. Host A sends an NS message. The source address is the unspecified address and the
destination address is the corresponding solicited-node multicast address of the IPv6 address
to be detected. The NS message body contains the detected IPv6 address.
2. If Host B uses this IPv6 address, Host B returns an NA message that contains its IPv6 address.
3. Host A knows 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 stateless address autoconfiguration
A node performs router/prefix discovery and stateless address autoconfiguration as follows:
1. At startup, a node sends an RS message to request configuration information from a router.
2. The router returns an RA message containing the Prefix Information option and other
configuration information. (The router also periodically sends an RA message.)
3. The node automatically generates an IPv6 address and other configuration parameters
according to the configuration information in the RA message.
The Prefix Information option contains an address prefix and the preferred lifetime and valid lifetime
of the address prefix. A node updates the preferred lifetime and valid lifetime upon receiving a
periodic RA message.
The generated IPv6 address is valid within the valid lifetime and becomes invalid when the valid
lifetime expires.
After the preferred lifetime expires, the node cannot use the generated IPv6 address to establish
new connections, but can receive packets destined for the IPv6 address. The preferred lifetime
cannot be greater than the valid lifetime.
Redirection
Upon receiving a packet from a host, the gateway sends an ICMPv6 redirect message to inform the
host of a better next hop when the following conditions are met:
•
The interface receiving the packet is the same as the interface forwarding the packet.
•
The selected route is not created or modified by an ICMPv6 redirect message.
•
The selected route is not a default route on the device.
•
The forwarded IPv6 packet does not contain the routing extension header.

IPv6 path MTU discovery

The links that a packet passes from a source to a destination can have different MTUs, among which
the minimum MTU is the path MTU. If a packet exceeds the path MTU, the source end fragments the
packet to reduce the processing pressure on intermediate devices and to use network resources
effectively.
A source end uses path MTU discovery to find the path MTU to a destination, as shown in
207
Figure 84.