Supporting IPv6 on a Linux Server Node

Back in 1996 when the first IETF specifications for IPv6 were done, there was an interest in having a test backbone for IPv6. During IETF-Montréal in 1996, the 6bone (IPv6 backbone) was born. It uses test (but still valid) addresses in the 3ffe::/16 range. At the beginning, most of the backbone was done using tunnels over the current IPv4 Internet. This makes a virtual IPv6 network over the IPv4 Internet. Nowadays, the 6bone is made of both native links and tunnel links. The 6bone is there for testing, so there is no service-level agreement between the organizations, but this doesn't mean it is not reliable or valid. Any traffic from and to 3ffe::/16 is valid without any limitation.

In July 1999, the three regional registries, ARIN for Americas, RIPE for Europe and Africa and APNIC for Asia, started to give regular nontest addresses to providers, starting in the 2001::/16 range. All the sites that have addresses from that range form the production IPv6 Internet.

To connect to either the 6bone or the IPv6 Internet, you need (as in IPv4) a provider that offers the service. If you can't find one directly, or if your current one does not offer the service, then the easy solution is to make a tunnel to a provider or a site that is willing to offer you the transit service.

As in the early days of the Internet, a project aimed to help people start using IPv6 is offering a free and automated tunnel service that can connect any individual or organization to the IPv6 Internet. The project is called Freenet6.net and is run by Viagénie, a consulting firm, as a free, volunteer and run-on-a-best-effort basis. The service is very popular in the community because of the easy and fast access to the Internet.

Freenet6 is modeled from the tunnel broker (RFC 3053) where an IPv6-over-IPv4 tunnel is established between a node and the tunnel broker. Freenet6 is an enhanced version where the node is using a tunnel setup protocol (TSP) to negotiate the establishment of the tunnel with the server. The client node may be a host or a router. The TSP server Freenet6 provides not only tunnels but also a large address space to any user of the service. The address space provided is a /48, which gives (16 bits) 65,536 subnets, each may have up to 264 nodes (64 bits). This is much more than the entire current Internet! This address space is assigned to the user and will survive over a change in the IPv4 address of the client node. This enables any user or organization to have the freedom of billions of addresses for servers and services; this was not easy to do with NAT in IPv4.

An IPv6-over-IPv4 tunnel is made with both end points configuring the IPv4 and the IPv6 address of the other end point. When one of the end points changes its IPv4 address, then both end points of the tunnel need to change their configuration accordingly. This is especially cumbersome when the IPv4 node is doing dial-up or changing addresses often. TSP, as implemented in the Freenet6 service, can be configured to take care of this. Each time the tunnel client changes its IPv4 address, for example, at boot time with DHCP service, the TSP client sends updated and authenticated information to the server, so the tunnel remains active. Supported client nodes of the Freenet6 service are Linux, FreeBSD, OpenBSD, NetBSD, Windows, Solaris and Cisco. Figure 7 illustrates the basic architecture of Freenet6.

Figure 7. Freenet6 Architecture with One Host

To use the Freenet6 service after installing IPv6 on Linux, you have to take the following steps. First, go to www.freenet6.net and register a user name. Then download the TSP client for Linux. Follow the instructions for compiling and installing it. Next, configure the tspc.conf file provided. Add your user name and password. Then start the tspc client:

tspc -vf tspc.conf

You may want to put the tspc client command in your boot sequence so that it will automatically re-enable the tunnel at boot time, even if your IPv4 address changes.

Freenet6 can give you either one IPv6 address if you have a host, or it can give you a full /48 if you have a router. Freenet6 will configure Linux to fit the role.

In the router case, you will receive a /48, and the first subnet on your router will be configured for router advertisements. This means that hosts on that subnet will receive the prefix and autoconfigure themselves, as shown in Figure 8.

Figure 8. Freenet6 Architecture with a Router and Multiple Hosts

There are many ways to connect to the IPv6 Internet. Freenet6, together with the TSP protocol, enables an easy IPv6-tunneled connection with a permanent address space so that if you change your IPv4 address, the IPv6 addresses and connection remains stable.