The IPv6 transition period has been developed to allow IPv6 to function within an IPv4 network without requiring any big changes to the existing network. In fact, only those nodes that will use IPv6 will need to be upgraded. Every other node on the network can be left alone, to be upgraded at a later time. Furthermore, those nodes that will never require direct access to the internet may never need to be upgraded. In this implementation, only a few nodes were made IPv6 capable and a tunnel was created to reach exterior IPv6 sites.

This section provides a complete description of the nodes that are important to an implementation. This IPv6 implementation was completed on the enst-bretagne.fr domain and the brestv6.enst-bretagne.fr subdomain. A network diagram of these domains is included to provide the reader with an overall view of the network and the implementation.

An IPv6 in IPv4 tunnel was created to allow IPv6 packets to be forwarded to exterior IPv6 sites. The IPv6 in IPv4 tunnel travels through local primary IPv4 router and ends at an exterior IPv6 node. The exterior IPv6 node may then forward the packet to the 6Bone through another IPv6 in IPv4 tunnel.

enst-bretagne.fr is primarily an IPv4 network. Only a few nodes in this domain offer IPv4/IPv6 co-existence. Every node in the brestv6.enst-bretagne.fr subdomain is IPv4/IPv6 capable. Figure 3.1 shows the nodes in the enst-bretagne.fr domain that are pertinent to this implementation.

This image illustrates the IPv6 network coexisting with the current IPv4 network. The IPv6 enabled machines can communicate with any machine on the network through IPv4, or IPv6 if the other machine is also IPv6 capable. The protocol used between IPv6 machines will vary, depending on the application initiating the link. In this fashion, applications that are not already functional in IPv6 can still use IPv4:

galaxie-eth0 is the primary router for all packets leaving the enst-bretagne.fr domain. galaxie-eth0 is not IPv6 capable. IPv6 packets with destinations outside of the local domain need an IPv6 in IPv4 tunnel to reach an exterior IPv6 destination. tourmalet is IPv4/IPv6 capable and provides an IPv6 in IPv4 tunnel to reach exterior IPv6 nodes. tourmalet is running Sun Solaris IPv6. pinfolab1 is a node on the enst-bretagne.fr domain that is IPv4/IPv6 capable. pinfolab1 tunnels through tourmalet to reach an exterior site. universe is the primary DNS for the enst-bretagne.fr domain, it does not contain any IPv6 information as it is not IPv6 capable.

portzic is the gateway that connects the enst-bretagne.fr and the brestv6.enst-bretagne.fr domains. This node has two interfaces, portzic and portzic-eth0. portzic resides on the enst-bretagne.fr domain, and portzic-eth0 resides on the brestv6.enst-bretagne.fr domain. Either of these names can be used to refer to the this gateway. pinfolab1 and portzic are both running Debian Linux/GNU 1.3 with kernel 2.1.99.

The IPv6 domain contains two systems, portzic-eth0 and venus, both are IPv6 capable. venus is running Sun Solaris IPv6. Communication between the two is primarily in IPv6: portzic-eth0 provides venus with Router Advertisements for the auto-configuration of its IPv6 interface: As mentioned above, portzic-eth0 is the gateway between the 192.168.100.0 network and the 192.44.75.0 network: All packets leaving venus are routed to portzic-eth0 which then forwards the IPv4 packets to the primary local router; galaxie-eth0. All local IPv6 packets are directly forwarded to their respective destination by portzic-eth0. Any IPv6 packets with a destination outside of the local IPv6 network are forwarded to tourmalet. tourmalet then forwards these packets through the IPv6 in IPv4 tunnel. The tunnel is further described in the next section:

The primary DNS for the brestv6.enst-bretagne.fr domain is portzic-eth0. This DNS contains IPv6 information for the all the IPv6 nodes in both the brestv6.enst-bretagne.fr and the enst-bretagne.fr domain. To facilitate IPv6 routing, pinfolab1 and tourmalet have been configured to use portzic-eth0 as their primary DNS.

In order to reach an exterior IPv6 site, the machines must route the packets through tourmalet. tourmalet has a tunnel to dedale.ipv6.enst-bretagne.fr, an IPv6 site at ENST-Br in Rennes, France: From Rennes, the packets may be forwarded to the 6 BONE through another IPv6 in IPv4 tunnel. Although the 6 BONE network is growing at a high rate, it is still very small when compared to the overall size of the current internet. Thus, routing paths through existing tunnels may take considerably longer than normal IPv4 routing paths.

To reach an IPv6 system that is not on the local network, an IPv6 tunnel is created to carry IPv6 data in the form of IPv4 packets. In this fashion, any IPv4 router can successfully process the information and forward the packets on their way to the IPv6 destination. Suppose venus wishes to communicate with an exterior system on the 6 BONE. venus would send an IPv6 packet to portzic-eth0, which would then forward the packet to tourmalet. Using the IPv6 in IPv4 tunnel configured at tourmalet, the packet would travel through galaxie-eth0 in IPv4 format. galaxie-eth0 would forward this packet as it would any other IPv4 packet. In this same fashion, pinfolab1 or any other local IPv6 node can reach an exterior IPv6 machine by routing an IPv6 packet through tourmalet.

No special configuration is necessary for galaxie-eth0, or any of the other IPv4 routers that the tunnel may cross. It is only necessary to configure the tunnel at the two IPv6 ends. In fact, it isn’t even necessary to configure tunneling for any of the other IPv6 nodes: tourmalet handles all of the tunneling for every IPv6 system on the local network. tourmalet controls IPv6 routing to an exterior source in the same way that galaxie-eth0 handles the IPv4 routing.

The implementation of IPv6 into the enst-bretagne.fr domain did not change the original network architecture. Nor was there any need to adapt any systems other than the IPv6 nodes themselves. This will allow the network to naturally evolve into IPv6 based on the needs of the local users. If a single user develops a necessity for IPv6, the node can be made IPv6 capable and configured to send all IPv6 packets to tourmalet. tourmalet will then route the packet accordingly. If a group or department decides to become IPv6 capable, a new IPv6 router can be created if necessary. All of the nodes in this department would be upgraded to IPv6 and configured to forward IPv6 packets to the local IPv6 router. The router can then be configured to forward to tourmalet, another local IPv6 host, or even a locally configured tunnel.

It is important to note that the difference between installing a new system and upgrading an existing IPv4 system. An existing system will already have its IPv4 address configured and registered with the local network. For a new system, the IPv4 network must be configured and registered accordingly for it to function. Although IPv6 may be correctly configured and registered with the IPv6 network, IPv4 will not function until it is also appropriately configured. This paper covers the IPv6 configuration of existing IPv4 nodes. Of course, IPv6 will function properly with or without an existing IPv4 network.