3Com S7906E - Switch, Configuration Manual

Page: 496 / 2621

1-2
z
The term tunnel used throughout this document refers to an IPv4/IPv6 transition tunnel, IPv4 over
IPv4 tunnel or IPv6 over IPv6 tunnel unless otherwise specified.
z
For information about MPLS TE, refer to MPLS TE Configuration in the MPLS Volume .
Introduction to IPv4/IPv6 Transition Tunnels
The expansion of the Internet results in scarce IPv4 addresses. The technologies such as temporary
IPv4 address allocation and Network Address Translation (NAT) relieve the problem of IPv4 address
shortage to some extent. However, these technologies not only increase the overhead in address
resolution and processing, but also lead to upper-layer application failures. Furthermore, they will still
face the problem that IPv4 addresses will eventually be used up. Internet Protocol Version 6 (IPv6)
adopting the 128-bit addressing scheme completely solves the above problem. Since significant
improvements have been made in address space, security, network management, mobility, and QoS,
IPv6 becomes one of the core standards for the next generation Internet protocol. IPv6 is compatible
with all protocols except IPv4 in the TCP/IP suite. Therefore, IPv6 can completely take the place of IPv4.
Before IPv6 becomes the dominant protocol, networks using the IPv6 protocol stack are expected to
communicate with the Internet using IPv4. Therefore, an IPv6-IPv4 interworking technology must be
developed to ensure the smooth transition from IPv4 to IPv6. In addition, the interworking technology
should provide efficient, seamless information transfer. Currently, multiple transition technologies and
interworking solutions are available. With their own characteristics, they are used to solve
communication problems in different transition stages under different environments.
Currently, there are three major transition technologies: dual stack (RFC 2893), tunneling (RFC 2893),
and NAT-PT (RFC 2766).
z
For related information about dual stack, refer to IPv6 Basics Configuration in the IP Services
Volume .
z
The S7900E series Ethernet switches do not support NAT-PT.
IPv6 over IPv4 Tunnel
Implementation
The IPv6 over IPv4 tunneling mechanism encapsulates an IPv4 header in IPv6 data packets so that
IPv6 packets can pass an IPv4 network through a tunnel to realize interworking between isolated IPv6
networks, as shown in Figure 1-1 .