Ipv6 Transition Technologies - HP A5120 EI Series Configuration Manual

Figure 55 PMTU discovery process
MTU = 1500
Source
Packet with MTU = 1500
ICMP error: packet too big;
The PMTU discovery works in the following steps.
The source host compares its MTU with the packet to be sent, performs necessary fragmentation,
1.
and sends the resulting packet to the destination host.
If the MTU supported by a forwarding interface is smaller than the packet, the switch discards the
2.
packet and returns an ICMPv6 error packet containing the interface MTU to the source host.
After receiving the ICMPv6 error packet, the source host uses the returned MTU to limit the packet
3.
size, performs fragmentation, and sends the resulting packet to the destination host.
Step 2 and step 3 are repeated until the destination host receives the packet. In this way, the
4.
source host decides the minimum MTU of all links in the path to the destination host.

IPv6 transition technologies

Before IPv6 dominates the Internet, efficient and seamless IPv6 transition technologies are needed to
enable communication between IPv4 and IPv6 networks. 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 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 is an encapsulation technology that utilizes one network protocol to encapsulate packets
of another network protocol, and then transfers them over the network.
Network Address Port Translation – Protocol Translation (NAPT-PT) is usually applied on a switch

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.
NOTE:
The A5120 EI Switch Series does not support NAT-PT and Tunneling.
MTU = 1500
use MTU = 1350
Packet with MTU = 1350
Packet received
MTU = 1350 MTU = 1400
119
Destination