H3C Technologies H3C SecPath F1000-E - Manual (Page 109)

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Figure 5 PMTU discovery process
The PMTU discovery process is:
1. The source host compares its MTU with the packet to be sent, performs necessary fragmentation,
and sends the resulting packet to the destination host.
2. If the MTU supported by a forwarding interface is smaller than the packet, the device discards the
packet and returns an ICMPv6 error packet containing the interface MTU to the source host.
3. After receiving the ICMPv6 error packet, the source host uses the returned MTU to limit the packet
size, performs fragmentation, and sends the resulting packet to the destination host.
4. Step 2 to step 3 are repeated until the destination host receives the packet. In this way, the source
host decides the minimum MTU of all links in the path to the destination host.
IPv6 Transition Technologies
Before IPv6 dominates the Internet, high-efficient, seamless IPv6 transition technologies are needed to
enable communication between IPv4 and IPv6 networks. There are several IPv6 transition technologies,
which can be used in different environments and periods, such as dual stack (RFC 2893), tunneling (RFC
2893), and NAT-PT (RFC 2766).
• Dual stack is the most direct transition approach. A network node that supports both IPv4 and IPv6
is called a dual stack node. A dual stack node configured with an IPv4 address and an IPv6
address can forward both IPv4 and IPv6 packets. For an upper layer application that supports both
IPv4 and IPv6, either TCP or UDP can be selected at the transport layer, whereas the IPv6 stack is
preferred at the network layer. Dual stack is suitable for communication between IPv4 nodes or
between IPv6 nodes. It is the basis of all transition technologies. However, it does not solve the IP
address depletion issue because each dual stack node must have a globally unique IP address.
• Tunneling is an encapsulation technology that utilizes one network protocol to encapsulate packets
of another network protocol and transfer them over the network. For more information about
tunneling, refer to Tunneling Configuration in the IP Services Volume.
• Network Address Port Translation – Protocol Translation (NAPT-PT) is usually applied on a device
between IPv4 and IPv6 networks to translate between IPv4 and IPv6 packets, allowing
communication between IPv4 and IPv6 nodes. It performs IP address translation, and according to
different protocols, performs semantic translation for packets. This technology is only suitable for
communication between a pure IPv4 node and a pure IPv6 node. For more information about
NAT-PT, refer to NAT-PT Configuration in the IP Services Volume.
Protocols and Standards
Protocols and standards related to IPv6 include: