H3C Technologies H3C SecPath F1000-E - Manual (Page 709)

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Figure 357 Path MTU discovery process
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 and 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. Several IPv6 transition technologies can be
used in different environments and periods, such as dual stack (RFC 2893), tunneling (RFC 2893),
NAT-PT (RFC 2766), and IPv6 on the provider edge routers (6PE).
Dual stack
Dual stack is the most direct transition approach. A network node that supports both IPv4 and IPv6 is 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 IPv4 address depletion issue because each dual
stack node must have a globally unique IP address.
Tunneling
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, see
VPN Configuration Guide.
NAT-PT
Network Address Translation – Protocol Translation (NAT-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, see NAT configuration Guide.