IPv6 Migration
Perhaps the most important study area for IPv6, beyond the core protocol
specifications, is how to integrate IPv6 into an IPv4 world.
From the project point of view, there are two aspects to the transition
or integration task. One is from the point of view of UKERNA, or the
Internet service or
access provider, in terms of what it needs to do to offer IPv6 to
the customer (university). The other is the university point of view;
what does it have to do to begin offering IPv6 services to its users,
and to allow them to communicate with the IPv4 world.
The ISP has a number of tools it can choose from, for example:
- Running IPv4 and IPv6 "dual stack" on its routers, thus also running
IPv4 and IPv6 over the same network links. This is currently problematic
in that no router vendors have yet released code with IPv6 support in
hardware.
- Tunnelling IPv6 in IPv4. This is attractive as the ISP can leverage
its IPv4 infrastructure to carry IPv6, but in doing so there is some
loss in efficiency, nor can you run IPv6 QoS. Tunnels can be configured manually, or via 6to4 (an automatic method that embeds the IPv4 endpoint address
in the IPv6 network prefix).
- Running a separate IPv6 network. THis is more expensive as it requires
additional equipment, but it will give the ISP the best insight into IPv6-only
network operation.
- Encapsulating IPv6 in MPLS, or similar methods. Both Cisco and Juniper
have appropriate MPLS technology (AToM and CCC).
- A tunnel broker, allowing a single host or a whole network to obtain
a tunnelled connection pseudo-automatically from visiting a web site.
The most well-known broker is freenet6.
The end site also has many methods to choose from, to allow access between
IPv4 and IPv6 systems, including:
- Dual-stack operation. If the site has ample IPv4 addresses, it can run
IPv4 and IPv6 on the same hosts.
- Dual Stack Transition Mechanism (DSTM). Uses dual-stack, but assigning
IPv4 addresses on demand from a pool of addresses.
- NAT-PT. Like IPv4 NAT, but with IP protocol translation also. This shares the same scalability concerns as IPv4 NAT, but for a small network it
performs adequately.
- Application layer gateways (ALGs). For example a web cache that can fetch
pages over IPv4 or over IPv6, or a dual-stack mail (SMTP) server.
- 6over4. Not to be confused with 6to4, this method runs IPv6 over multicast IPv4 - not popular as IPv4 multicast is not commonly deployed (used) on sites.
On Bermuda, we have set up an IPv6 tunnel broker, run 6to4 with a 6to4 relay
server, NAT-PT, application layer gateways and general dual-stack systems.
Some of those access services can be seen here.
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